Google示例SlidingTabsColors分析

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/*
 * Copyright 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.slidingtabscolors;

import com.example.android.common.view.SlidingTabLayout;

import android.graphics.Color;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import java.util.ArrayList;
import java.util.List;

/**
 * A basic sample which shows how to use {@link com.example.android.common.view.SlidingTabLayout}
 * to display a custom {@link ViewPager} title strip which gives continuous feedback to the user
 * when scrolling.
 */
public class SlidingTabsColorsFragment extends Fragment {

    /**
     * This class represents a tab to be displayed by {@link ViewPager} and it‘s associated
     * {@link SlidingTabLayout}.
     * 这个类代表了一个tab通过ViewPager去显示，它和SlidingTabLayout相关联
     */
    static class SamplePagerItem {
        private final CharSequence mTitle;//pager title
        private final int mIndicatorColor;//pager indicator color
        private final int mDividerColor;

        SamplePagerItem(CharSequence title, int indicatorColor, int dividerColor) {
            mTitle = title;
            mIndicatorColor = indicatorColor;
            mDividerColor = dividerColor;
        }

        /**
         * @return A new {@link Fragment} to be displayed by a {@link ViewPager}
         * 返回一个新的Fragment通过ViewPager去显示
         */
        Fragment createFragment() {
            return ContentFragment.newInstance(mTitle, mIndicatorColor, mDividerColor);
        }

        /**
         * @return the title which represents this tab. In this sample this is used directly by
         * {@link android.support.v4.view.PagerAdapter#getPageTitle(int)}
         */
        CharSequence getTitle() {
            return mTitle;
        }

        /**
         * @return the color to be used for indicator on the {@link SlidingTabLayout}
         */
        int getIndicatorColor() {
            return mIndicatorColor;
        }

        /**
         * @return the color to be used for right divider on the {@link SlidingTabLayout}
         */
        int getDividerColor() {
            return mDividerColor;
        }
    }

    static final String LOG_TAG = "SlidingTabsColorsFragment";

    /**
     * A custom {@link ViewPager} title strip which looks much like Tabs present in Android v4.0 and
     * above, but is designed to give continuous feedback to the user when scrolling.
     */
    private SlidingTabLayout mSlidingTabLayout;

    /**
     * A {@link ViewPager} which will be used in conjunction with the {@link SlidingTabLayout} above.
     */
    private ViewPager mViewPager;

    /**
     * List of {@link SamplePagerItem} which represent this sample‘s tabs.
     */
    private List<SamplePagerItem> mTabs = new ArrayList<SamplePagerItem>();

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // BEGIN_INCLUDE (populate_tabs)
        /**
         * Populate our tab list with tabs. Each item contains a title, indicator color and divider
         * color, which are used by {@link SlidingTabLayout}.
         * 使用我们的tab填充tabs列表，每个条目包含一个标题，指示器颜色，和分割线颜色
         */
        mTabs.add(new SamplePagerItem(
                getString(R.string.tab_stream), // Title
                Color.BLUE, // Indicator color
                Color.GRAY // Divider color
        ));

        mTabs.add(new SamplePagerItem(
                getString(R.string.tab_messages), // Title
                Color.RED, // Indicator color
                Color.GRAY // Divider color
        ));

        mTabs.add(new SamplePagerItem(
                getString(R.string.tab_photos), // Title
                Color.YELLOW, // Indicator color
                Color.GRAY // Divider color
        ));

        mTabs.add(new SamplePagerItem(
                getString(R.string.tab_notifications), // Title
                Color.GREEN, // Indicator color
                Color.GRAY // Divider color
        ));
        // END_INCLUDE (populate_tabs)
    }

    /**
     * Inflates the {@link View} which will be displayed by this {@link Fragment}, from the app‘s
     * resources.
     */
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_sample, container, false);
    }

    // BEGIN_INCLUDE (fragment_onviewcreated)
    /**
     * This is called after the {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)} has finished.
     * Here we can pick out the {@link View}s we need to configure from the content view.
     *
     * We set the {@link ViewPager}‘s adapter to be an instance of
     * {@link SampleFragmentPagerAdapter}. The {@link SlidingTabLayout} is then given the
     * {@link ViewPager} so that it can populate itself.
     *
     * @param view View created in {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)}
     */
    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        // BEGIN_INCLUDE (setup_viewpager)
        // Get the ViewPager and set it‘s PagerAdapter so that it can display items
        mViewPager = (ViewPager) view.findViewById(R.id.viewpager);
        mViewPager.setAdapter(new SampleFragmentPagerAdapter(getChildFragmentManager()));
        // END_INCLUDE (setup_viewpager)

        // BEGIN_INCLUDE (setup_slidingtablayout)
        // Give the SlidingTabLayout the ViewPager, this must be done AFTER the ViewPager has had
        // it‘s PagerAdapter set.这必须在Viewpager的adapter被设置之后
        mSlidingTabLayout = (SlidingTabLayout) view.findViewById(R.id.sliding_tabs);
        mSlidingTabLayout.setViewPager(mViewPager);
        mSlidingTabLayout.setCustomTextViewColor(Color.RED,Color.BLACK);

        // BEGIN_INCLUDE (tab_colorizer)
        // Set a TabColorizer to customize the indicator and divider colors. Here we just retrieve
        // the tab at the position, and return it‘s set color
        mSlidingTabLayout.setCustomTabColorizer(new SlidingTabLayout.TabColorizer() {

            @Override
            public int getIndicatorColor(int position) {
                return mTabs.get(position).getIndicatorColor();
            }

            @Override
            public int getDividerColor(int position) {
                return mTabs.get(position).getDividerColor();
            }

        });
        // END_INCLUDE (tab_colorizer)
        // END_INCLUDE (setup_slidingtablayout)
    }
    // END_INCLUDE (fragment_onviewcreated)

    /**
     * The {@link FragmentPagerAdapter} used to display pages in this sample. The individual pages
     * are instances of {@link ContentFragment} which just display three lines of text. Each page is
     * created by the relevant {@link SamplePagerItem} for the requested position.
     * <p>
     * The important section of this class is the {@link #getPageTitle(int)} method which controls
     * what is displayed in the {@link SlidingTabLayout}.
     */
    class SampleFragmentPagerAdapter extends FragmentPagerAdapter {

        SampleFragmentPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        /**
         * Return the {@link android.support.v4.app.Fragment} to be displayed at {@code position}.
         * <p>
         * Here we return the value returned from {@link SamplePagerItem#createFragment()}.
         */
        @Override
        public Fragment getItem(int i) {
            return mTabs.get(i).createFragment();
        }

        @Override
        public int getCount() {
            return mTabs.size();
        }

        // BEGIN_INCLUDE (pageradapter_getpagetitle)
        /**
         * Return the title of the item at {@code position}. This is important as what this method
         * returns is what is displayed in the {@link SlidingTabLayout}.
         * <p>
         * Here we return the value returned from {@link SamplePagerItem#getTitle()}.
         */
        @Override
        public CharSequence getPageTitle(int position) {
            return mTabs.get(position).getTitle();
        }
        // END_INCLUDE (pageradapter_getptle)

    }

}

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.common.view;

import android.content.Context;
import android.graphics.Color;
import android.graphics.Typeface;
import android.os.Build;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.HorizontalScrollView;
import android.widget.TextView;

import com.example.android.common.logger.Log;

/**
 * To be used with ViewPager to provide a tab indicator component which give constant feedback as to
 * the user‘s scroll progress.
 * <p>
 * To use the component, simply add it to your view hierarchy. Then in your
 * {@link android.app.Activity} or {@link android.support.v4.app.Fragment} call
 * {@link #setViewPager(ViewPager)} providing it the ViewPager this layout is being used for.
 * <p>
 * The colors can be customized in two ways. The first and simplest is to provide an array of colors
 * via {@link #setSelectedIndicatorColors(int...)} and {@link #setDividerColors(int...)}. The
 * alternative is via the {@link TabColorizer} interface which provides you complete control over
 * which color is used for any individual position.
 * <p>
 * The views used as tabs can be customized by calling {@link #setCustomTabView(int, int)},
 * providing the layout ID of your custom layout.
 *
 * just like list
 *
 * 本类作用：
 * 将SlidingTabStrip作为子类添加到本类
 * 在本类中根据PagerAdapter的大小生成TextView添加到SlidingTabStrip中，并设置TextView的点击监听和设置ViewPager.OnPageChangeListener监听器
 * 在PageChange监听器中控制TextView的移动和调用SlidingTabStrip中的相应方法
 */
public class SlidingTabLayout extends HorizontalScrollView {

    /**
     * Allows complete control over the colors drawn in the tab layout. Set with
     * {@link #setCustomTabColorizer(TabColorizer)}.
     */
    public interface TabColorizer {

        /**
         * @return return the color of the indicator used when {@code position} is selected.
         */
        int getIndicatorColor(int position);

        /**
         * @return return the color of the divider drawn to the right of {@code position}.
         */
        int getDividerColor(int position);

    }

    private static final int TITLE_OFFSET_DIPS = 24;
    // view padding
    private static final int TAB_VIEW_PADDING_DIPS = 16;
    // text size
    private static final int TAB_VIEW_TEXT_SIZE_SP = 12;

    private static final int TAB_VIEW_DEFAULT_TEXT_COLOR = Color.BLACK;

    private int mTitleOffset;

    private int mTabViewLayoutId;
    private int mTabViewTextViewId;

    private int mTabTextViewFocusColor;
    private int mTabTextViewUnFocusColor;

    private ViewPager mViewPager;
    private ViewPager.OnPageChangeListener mViewPagerPageChangeListener;

    private final SlidingTabStrip mTabStrip;

    public SlidingTabLayout(Context context) {
        this(context, null);
    }

    public SlidingTabLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public SlidingTabLayout(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        // Disable the Scroll Bar
        // Define whether the horizontal scrollbar should be drawn or not.
        // The scrollbar is not drawn by default.
        // 定义水平滚动栏是否应该被绘制
        setHorizontalScrollBarEnabled(false);
        // Make sure that the Tab Strips fills this View
        // 表明这个HorizontalScrollView是否应该拉伸它的内容宽度去填充视图
        setFillViewport(true);

        mTitleOffset = (int) (TITLE_OFFSET_DIPS * getResources().getDisplayMetrics().density);

        mTabStrip = new SlidingTabStrip(context);
        //将mTabStrip添加到本容器中
        addView(mTabStrip, LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
    }

    /**
     * Set the custom {@link TabColorizer} to be used.
     *
     * If you only require simple custmisation then you can use
     * {@link #setSelectedIndicatorColors(int...)} and {@link #setDividerColors(int...)} to achieve
     * similar effects.
     *
     * set TabColorizer into SlidingTabStrip container
     */
    public void setCustomTabColorizer(TabColorizer tabColorizer) {
        mTabStrip.setCustomTabColorizer(tabColorizer);
    }

    /**
     * Sets the colors to be used for indicating the selected tab. These colors are treated as a
     * circular array. Providing one color will mean that all tabs are indicated with the same color.
     */
    public void setSelectedIndicatorColors(int... colors) {
        mTabStrip.setSelectedIndicatorColors(colors);
    }

    /**
     * Sets the colors to be used for tab dividers. These colors are treated as a circular array.
     * Providing one color will mean that all tabs are indicated with the same color.
     */
    public void setDividerColors(int... colors) {
        mTabStrip.setDividerColors(colors);
    }

    /**
     * Set the {@link ViewPager.OnPageChangeListener}. When using {@link SlidingTabLayout} you are
     * required to set any {@link ViewPager.OnPageChangeListener} through this method. This is so
     * that the layout can update it‘s scroll position correctly.
     *
     * @see ViewPager#setOnPageChangeListener(ViewPager.OnPageChangeListener)
     *
     * 为本类中的监听器赋值
     */
    public void setOnPageChangeListener(ViewPager.OnPageChangeListener listener) {
        mViewPagerPageChangeListener = listener;
    }

    /**
     * Set the custom layout to be inflated for the tab views.
     *
     * @param layoutResId Layout id to be inflated
     * @param textViewId id of the {@link TextView} in the inflated view
     */
    public void setCustomTabView(int layoutResId, int textViewId) {
        mTabViewLayoutId = layoutResId;
        mTabViewTextViewId = textViewId;
    }

    /**
     *
     * @param focusColor 焦点的颜色
     * @param unfocusCilor 非焦点的颜色
     */
    public void setCustomTextViewColor(int focusColor,int unfocusCilor){
        mTabTextViewFocusColor = focusColor;
        mTabTextViewUnFocusColor = unfocusCilor;
    }

    /**
     * Sets the associated view pager. Note that the assumption here is that the pager content
     * (number of tabs and tab titles) does not change after this call has been made.
     * 注意调用这个方法后pager的内容没有改变
     *
     * remove all view in container and set listener for viewpager
     */
    public void setViewPager(ViewPager viewPager) {
        mTabStrip.removeAllViews();

        mViewPager = viewPager;
        if (viewPager != null) {
            viewPager.setOnPageChangeListener(new InternalViewPagerListener());
            populateTabStrip();
        }
    }

    /**
     * Create a default view to be used for tabs. This is called if a custom tab view is not set via
     * {@link #setCustomTabView(int, int)}.
     * 创建tabs使用的一个默认的TextView，如果没有通过setCustomTabView(int, int)设置一个自定义的tab view这将被调用
     */
    protected TextView createDefaultTabView(Context context) {
        TextView textView = new TextView(context);
        textView.setGravity(Gravity.CENTER);
        textView.setTextSize(TypedValue.COMPLEX_UNIT_SP, TAB_VIEW_TEXT_SIZE_SP);
        textView.setTypeface(Typeface.DEFAULT_BOLD);

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
            // If we‘re running on Honeycomb or newer, then we can use the Theme‘s
            // selectableItemBackground to ensure that the View has a pressed state
            // 如果我们运行在3.0或者以上的版本，那么我们可以使用主题的selectableItemBackground去确保View有一个按下的状态
            TypedValue outValue = new TypedValue();
            getContext().getTheme().resolveAttribute(android.R.attr.selectableItemBackground,
                    outValue, true);
            textView.setBackgroundResource(outValue.resourceId);
        }

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
            // If we‘re running on ICS or newer, enable all-caps to match the Action Bar tab style
            //如果我们运行在4.0或者4.0版本以上，Action Bar的tab的所有字母大写样式可用
            textView.setAllCaps(true);
        }

        int padding = (int) (TAB_VIEW_PADDING_DIPS * getResources().getDisplayMetrics().density);
        textView.setPadding(padding, padding, padding, padding);

        return textView;
    }

    /**
     * 根据PagerAdapter的数量，得到tabview并设置它的标题，设置监听器，添加到SlidingTabStrip中
     */
    private void populateTabStrip() {
        final PagerAdapter adapter = mViewPager.getAdapter();
        final View.OnClickListener tabClickListener = new TabClickListener();

        for (int i = 0; i < adapter.getCount(); i++) {
            View tabView = null;
            TextView tabTitleView = null;

            //如果自定义的mTabViewLayoutId有值，则使用自定义的布局
            if (mTabViewLayoutId != 0) {
                // If there is a custom tab view layout id set, try and inflate it
                // 如果这里有自定义的tab的视图布局id，尝试去填充它
                tabView = LayoutInflater.from(getContext()).inflate(mTabViewLayoutId, mTabStrip,
                        false);
                tabTitleView = (TextView) tabView.findViewById(mTabViewTextViewId);
            }
            //如果tabView没有赋值，则创建默认的TabView
            if (tabView == null) {
                tabView = createDefaultTabView(getContext());
            }

            if (tabTitleView == null && TextView.class.isInstance(tabView)) {
                tabTitleView = (TextView) tabView;
            }

            //设置标题和监听器
            tabTitleView.setText(adapter.getPageTitle(i));

            tabView.setOnClickListener(tabClickListener);
            //添加到SlidingTabStrip中
            mTabStrip.addView(tabView);
        }
    }

    /**
     * This is called when the view is attached to a window.
     * At this point it has a Surface and will start drawing.
     * Note that this function is guaranteed to be called before onDraw(android.graphics.Canvas),
     * however it may be called any time before the first onDraw --
     * including before or after onMeasure(int, int)
     *
     * 当一个view被附着到window上的时候被调用。
     *
     * 注意这个功能被保证在onDraw(android.graphics.Canvas)之前调用，但是它可能在第一次onDraw方法之前的任何时候被调用
     * 包括onMeasure(int, int)之前或者之后
     */
    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();

        if (mViewPager != null) {
            scrollToTab(mViewPager.getCurrentItem(), 0);
        }
    }

    /**
     * 控制TextView的滚动
     * @param tabIndex
     * @param positionOffset
     */
    private void scrollToTab(int tabIndex, int positionOffset) {
        final int tabStripChildCount = mTabStrip.getChildCount();
        //不可以小于0 大于子类的数量
        if (tabStripChildCount == 0 || tabIndex < 0 || tabIndex >= tabStripChildCount) {
            return;
        }

        //得到当前的View
        View selectedChild = mTabStrip.getChildAt(tabIndex);
        if (selectedChild != null) {
            int targetScrollX = selectedChild.getLeft() + positionOffset;

            if (tabIndex > 0 || positionOffset > 0) {
                // If we‘re not at the first child and are mid-scroll, make sure we obey the offset
                // 如果我们不在第一个子类或者中间滚动，确定服从位移.mTitleOffset为24dp
                targetScrollX -= mTitleOffset;
            }

            //为什么向左滚动滚动完成后才设置颜色，向右滚动开始滚动就已经开始设置颜色
            //因为向左滚动的时候滚动完成position才变成position＋1，向右滚动开始滚动position就变成position－1了
            if(positionOffset == 0)
                setTabTextColor((TextView) selectedChild,tabIndex);

            //滚动到指定的坐标位置
            scrollTo(targetScrollX, 0);
        }
    }

    /**
     * 设置文本的颜色
     */
    public void setTabTextColor(TextView selectedChild,int tabIndex){
        if(mTabTextViewFocusColor == 0){
            mTabTextViewFocusColor = TAB_VIEW_DEFAULT_TEXT_COLOR;
        }
        if(mTabTextViewUnFocusColor == 0){
            mTabTextViewUnFocusColor = TAB_VIEW_DEFAULT_TEXT_COLOR;
        }
        selectedChild.setTextColor(mTabTextViewFocusColor);
        for (int i = 0; i < mTabStrip.getChildCount(); i++) {
            if(i != tabIndex){
                TextView unfocusText = (TextView) mTabStrip.getChildAt(i);
                unfocusText.setTextColor(mTabTextViewUnFocusColor);
            }
        }
    }

    /**
     * 实现了OnPageChangeListener监听器
     */
    private class InternalViewPagerListener implements ViewPager.OnPageChangeListener {
        private int mScrollState;

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            int tabStripChildCount = mTabStrip.getChildCount();
            if ((tabStripChildCount == 0) || (position < 0) || (position >= tabStripChildCount)) {
                return;
            }

            //ViewPager滚动的时候positionOffset值为0～1之间
            mTabStrip.onViewPagerPageChanged(position, positionOffset);

            View selectedTitle = mTabStrip.getChildAt(position);
            //positionOffset如果从0～1表示向左滑，1～0表示向右滑
            int extraOffset = (selectedTitle != null)
                    ? (int) (positionOffset * selectedTitle.getWidth())
                    : 0;

            scrollToTab(position, extraOffset);

            if (mViewPagerPageChangeListener != null) {
                mViewPagerPageChangeListener.onPageScrolled(position, positionOffset,
                        positionOffsetPixels);
            }
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            mScrollState = state;

            if (mViewPagerPageChangeListener != null) {
                mViewPagerPageChangeListener.onPageScrollStateChanged(state);
            }
        }

        @Override
        public void onPageSelected(int position) {
            /**
             * Indicates that the pager is in an idle, settled state.
             * The current page is fully in view and no animation is in progress.
             * 表明页面为空闲状态，停止状态，当前页面已经完全在view中，没有动画正在进行中
             */
            if (mScrollState == ViewPager.SCROLL_STATE_IDLE) {
                mTabStrip.onViewPagerPageChanged(position, 0f);
                scrollToTab(position, 0);
            }

            if (mViewPagerPageChangeListener != null) {
                mViewPagerPageChangeListener.onPageSelected(position);
            }
        }

    }

    /**
     * tab click listener
     */
    private class TabClickListener implements View.OnClickListener {
        @Override
        public void onClick(View v) {
            for (int i = 0; i < mTabStrip.getChildCount(); i++) {
                //judge which view is clicked
                if (v == mTabStrip.getChildAt(i)) {
                    mViewPager.setCurrentItem(i);
                    return;
                }
            }
        }
    }

}

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.common.view;

import android.R;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.View;
import android.widget.LinearLayout;

/**
 * 本类作用：
 * 绘制分割线，绘制底部指示器，绘制底部边界
 */
class SlidingTabStrip extends LinearLayout {

    /**
     * 默认底部边界的厚度（宽度）
     */
    private static final int DEFAULT_BOTTOM_BORDER_THICKNESS_DIPS = 2;
    /**
     * 默认底部边界颜色的透明度
     */
    private static final byte DEFAULT_BOTTOM_BORDER_COLOR_ALPHA = 0x26;
    /**
     * 已选指示器的厚度
     */
    private static final int SELECTED_INDICATOR_THICKNESS_DIPS = 8;
    /**
     * 默认已选指示器的颜色
     */
    private static final int DEFAULT_SELECTED_INDICATOR_COLOR = 0xFF33B5E5;
    /**
     * 默认分割线的厚度
     */
    private static final int DEFAULT_DIVIDER_THICKNESS_DIPS = 1;
    /**
     * 默认分割线颜色的透明度
     */
    private static final byte DEFAULT_DIVIDER_COLOR_ALPHA = 0x20;
    /**
     * 默认分割线的高度
     */
    private static final float DEFAULT_DIVIDER_HEIGHT = 0.5f;
    /**
     * 底部边界的高度
     */
    private final int mBottomBorderThickness;
    /**
     * 默认底部边界的画笔
     */
    private final Paint mBottomBorderPaint;
    /**
     * 已选指示器的高度
     */
    private final int mSelectedIndicatorThickness;
    /**
     * 已选指示器的画笔
     */
    private final Paint mSelectedIndicatorPaint;
    /**
     * 默认底部边界的颜色
     */
    private final int mDefaultBottomBorderColor;
    /**
     * 分割线的画笔
     */
    private final Paint mDividerPaint;
    /**
     * 分割线的高度
     */
    private final float mDividerHeight;
    /**
     * 选择的位置
     */
    private int mSelectedPosition;
    /**
     * 选择的位移
     */
    private float mSelectionOffset;
    /**
     * 自定义的Tab样式
     */
    private SlidingTabLayout.TabColorizer mCustomTabColorizer;
    /**
     * 默认的Tab样式
     */
    private final SimpleTabColorizer mDefaultTabColorizer;

    SlidingTabStrip(Context context) {
        this(context, null);
    }

    SlidingTabStrip(Context context, AttributeSet attrs) {
        super(context, attrs);
        //如果这个view不需要绘制任何东西，那么设置这个标志去允许进一步的优化
        setWillNotDraw(false);

        final float density = getResources().getDisplayMetrics().density;

        //动态类型数据值的容器，主要被用于Resources去持有资源值
        TypedValue outValue = new TypedValue();
        context.getTheme().resolveAttribute(R.attr.colorForeground, outValue, true);
        final int themeForegroundColor =  outValue.data;

        //混合主题的前景颜色和默认的底部边界颜色的透明度，默认的底部边界颜色
        mDefaultBottomBorderColor = setColorAlpha(themeForegroundColor,
                DEFAULT_BOTTOM_BORDER_COLOR_ALPHA);

        //默认的SimpleTabColorizer，指示器颜色为0xFF33B5E5，默认的分割线的颜色为主题的前景色和0x20混合的颜色
        mDefaultTabColorizer = new SimpleTabColorizer();
        mDefaultTabColorizer.setIndicatorColors(DEFAULT_SELECTED_INDICATOR_COLOR);
        mDefaultTabColorizer.setDividerColors(setColorAlpha(themeForegroundColor,
                DEFAULT_DIVIDER_COLOR_ALPHA));

        //默认的底部高度
        mBottomBorderThickness = (int) (DEFAULT_BOTTOM_BORDER_THICKNESS_DIPS * density);
        mBottomBorderPaint = new Paint();
        mBottomBorderPaint.setColor(mDefaultBottomBorderColor);

        mSelectedIndicatorThickness = (int) (SELECTED_INDICATOR_THICKNESS_DIPS * density);
        mSelectedIndicatorPaint = new Paint();

        //分割先的高度和画笔
        mDividerHeight = DEFAULT_DIVIDER_HEIGHT;
        mDividerPaint = new Paint();
        mDividerPaint.setStrokeWidth((int) (DEFAULT_DIVIDER_THICKNESS_DIPS * density));
    }

    /**
     * 设置自定义的颜色样式并重绘
     * @param customTabColorizer
     */
    void setCustomTabColorizer(SlidingTabLayout.TabColorizer customTabColorizer) {
        mCustomTabColorizer = customTabColorizer;
        invalidate();
    }

    /**
     * 设置已选的指示器颜色并重绘
     * @param colors
     */
    void setSelectedIndicatorColors(int... colors) {
        // Make sure that the custom colorizer is removed
        mCustomTabColorizer = null;
        mDefaultTabColorizer.setIndicatorColors(colors);
        invalidate();
    }

    /**
     * 设置分割线的颜色
     * @param colors
     */
    void setDividerColors(int... colors) {
        // Make sure that the custom colorizer is removed
        mCustomTabColorizer = null;
        mDefaultTabColorizer.setDividerColors(colors);
        invalidate();
    }


    /**
     * ViewPager页面改变的时候，传递的位置和位置偏移量
     * @param position 向左滚动的时候滚动完成position才变成position＋1，向右滚动开始滚动position就变成position－1了
     * @param positionOffset ViewPager页面改变的时候的positionOffset，如果从0～1表示向左滑，1～0表示向右滑
     */
    void onViewPagerPageChanged(int position, float positionOffset) {
        mSelectedPosition = position;
        mSelectionOffset = positionOffset;
        invalidate();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        final int height = getHeight();
        final int childCount = getChildCount();
        final int dividerHeightPx = (int) (Math.min(Math.max(0f, mDividerHeight), 1f) * height);

        // 如果自定义的TabColorizer为null，则选择默认的TabColorizer
        final SlidingTabLayout.TabColorizer tabColorizer = mCustomTabColorizer != null
                ? mCustomTabColorizer
                : mDefaultTabColorizer;

        // Thick colored underline below the current selection
        if (childCount > 0) {
            View selectedTitle = getChildAt(mSelectedPosition);
            int left = selectedTitle.getLeft();
            int right = selectedTitle.getRight();
            int color = tabColorizer.getIndicatorColor(mSelectedPosition);

            //mSelectionOffset > 0f用于判断是否在移动
            if (mSelectionOffset > 0f && mSelectedPosition < (getChildCount() - 1)) {
                int nextColor = tabColorizer.getIndicatorColor(mSelectedPosition + 1);
                //如果两个颜色不相同的话，混合颜色
                if (color != nextColor) {
                    color = blendColors(nextColor, color, mSelectionOffset);
                }

                // Draw the selection partway between the tabs，得到下一个
                View nextTitle = getChildAt(mSelectedPosition + 1);
                // 计算指示器底部移动条的宽度，比如mSelectionOffset为0.7，就是0.7乘以后一个View的宽度加上0.3乘以前一个View的宽度
                left = (int) (mSelectionOffset * nextTitle.getLeft() +
                        (1.0f - mSelectionOffset) * left);
                right = (int) (mSelectionOffset * nextTitle.getRight() +
                        (1.0f - mSelectionOffset) * right);
            }

            mSelectedIndicatorPaint.setColor(color);

            //绘制指示器底部的矩形
            canvas.drawRect(left, height - mSelectedIndicatorThickness, right,
                    height, mSelectedIndicatorPaint);
        }

        // Thin underline along the entire bottom edge，底部一条长的分割线
        canvas.drawRect(0, height - mBottomBorderThickness, getWidth(), height, mBottomBorderPaint);

        // Vertical separators between the titles
        int separatorTop = (height - dividerHeightPx) / 2;
        // 绘制分割线
        for (int i = 0; i < childCount - 1; i++) {
            View child = getChildAt(i);
            mDividerPaint.setColor(tabColorizer.getDividerColor(i));
            canvas.drawLine(child.getRight(), separatorTop, child.getRight(),
                    separatorTop + dividerHeightPx, mDividerPaint);
        }
    }

    /**
     * Set the alpha value of the {@code color} to be the given {@code alpha} value.
     * 使用argb (int alpha, int red, int green, int blue)方法生成一个新的颜色
     */
    private static int setColorAlpha(int color, byte alpha) {
        return Color.argb(alpha, Color.red(color), Color.green(color), Color.blue(color));
    }

    /**
     * Blend {@code color1} and {@code color2} using the given ratio.
     * 使用给定的比率混合color1和color2
     *
     * @param ratio of which to blend. 1.0 will return {@code color1}, 0.5 will give an even blend,
     *              0.0 will return {@code color2}.
     */
    private static int blendColors(int color1, int color2, float ratio) {
        final float inverseRation = 1f - ratio;
        //该算法实现渐变的效果
        float r = (Color.red(color1) * ratio) + (Color.red(color2) * inverseRation);
        float g = (Color.green(color1) * ratio) + (Color.green(color2) * inverseRation);
        float b = (Color.blue(color1) * ratio) + (Color.blue(color2) * inverseRation);
        return Color.rgb((int) r, (int) g, (int) b);
    }

    /**
     * 实现了SlidingTabLayout.TabColorizer，保存指示器的颜色数组，分割线的颜色数组
     */
    private static class SimpleTabColorizer implements SlidingTabLayout.TabColorizer {
        private int[] mIndicatorColors;
        private int[] mDividerColors;

        /**
         * 设计相当精妙，使用位置取余mIndicatorColors数组的长度，不用担心数组越界的情况
         * @param position
         * @return
         */
        @Override
        public final int getIndicatorColor(int position) {
            return mIndicatorColors[position % mIndicatorColors.length];
        }

        @Override
        public final int getDividerColor(int position) {
            return mDividerColors[position % mDividerColors.length];
        }

        void setIndicatorColors(int... colors) {
            mIndicatorColors = colors;
        }

        void setDividerColors(int... colors) {
            mDividerColors = colors;
        }
    }
}

Google示例SlidingTabsColors分析

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原文地址：http://blog.csdn.net/u010121444/article/details/51353545