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魅族手机的闹钟应用中有个倒计时，这个控件还是蛮有趣的。左边是魅族闹钟，右边是我们最终实现的效果，虽然有些细节还需优化，不过基本上已经达到了想要的效果，我们先来就来看看如何实现吧。
对一个Android自定义控件来说，一般都经过三个步骤
onLayout()
onMeasure()
onDraw()
onLayout明确子控件在父控件中的位置（本控件不需要重写），onMeasure是确定控件的大小（宽、高），而onDraw是我们重点关注的方法，我们需要在这个方法中写入显示View的逻辑代码。
对于本控件，控件的高度 应该等于细线的高度(mLineHeight)加上数字的高度（mFontHeight），当然为了好看，中间需要设上一些边距(mPadding)，因此本控件的高度应该为 mFontHeight + mLineHeight + 10 + mPadding，测量代码如下
private int measureHeight(int heightMeasureSpec) {
int mode = MeasureSpec.getMode(heightMeasureSpec);
int size = MeasureSpec.getSize(heightMeasureSpec);
switch (mode) {
case MeasureSpec.EXACTLY:
return size ;
case MeasureSpec.AT_MOST:
return Math.min(size, mFontHeight + mLineHeight + 10 + mPadding) ;
}
return size ;
}
同样地，控件的宽度其实就是0~1000的间隔，测量代码如下
private int measureWidth(int widthMeasureSpec) {
int mode = MeasureSpec.getMode(widthMeasureSpec);
int size = MeasureSpec.getSize(widthMeasureSpec);
switch (mode) {
case MeasureSpec.EXACTLY:
return size ;
case MeasureSpec.AT_MOST:
int result = getPaddingLeft() + mContentWidth + getPaddingRight() ;
return Math.min(size, result) ;
}
return size ;
}
重点在于刻度尺的计算。思路是先draw上头的数字，然后再draw下边的线条，判断位置确定是否需要draw上头的数字即可。其实就是坐标的计算。代码如下
int startX = mPadding;
int stopX = mPadding;
int stopY =mHeight - mPadding;
for (int i = 0 ; i<=mContentWidth ; i += mFontWidth)
if (i % (mFontWidth *10) == 0) {
canvas.drawLine(startX + i, mFontHeight + mPadding + 5 , stopX + i, stopY, mTextPaint);
canvas.drawText(i + "", startX + i, mFontHeight + mPadding, mTextPaint);
} else if (i % mFontWidth == 0) {
canvas.drawLine(startX + i, mFontHeight + mPadding + 10, stopX + i, stopY, mPaint);
}
Android本身提供了移动View的API，因此让View动起来也是不难的。两种思路
监听Touch事件，当Touch坐标变化时，计算坐标位置，不断调用scrollTo(x,0)达到变换坐标的目的
监听Touch事件，记录上次横坐标和本次横坐标的差值，然后调用scrollBy(delta， 0) 即可移动
其实两种方法本质上都是一样的。ScrollBy其实也是调用了scrollTo方法。本文采用方法二。其代码如下
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mLastX = (int) event.getX();
break;
case MotionEvent.ACTION_MOVE:
int x = (int) event.getX();
int deltaX = x - mLastX;
scrollBy(-deltaX, 0);
mLastX = x;
break;
}
return true;
}
当然了，我们是不能让View无限移动的，因此需要重写scrollBy方法，限制View不能超过边界。
代码如下
@Override
public void scrollBy(int x, int y) {
super.scrollBy(x, y);
if (x < 0) { // drag to left
if (getScrollX() < -getCenter() + mPadding) {
scrollTo(-getCenter() + mPadding, 0);
}
} else
if (x >0) { // drag to right
if (mContentWidth - getScrollX() + x < getCenter()) {
scrollTo(mContentWidth - getCenter() + mFontWidth, 0);
}
}
}
当超过边界时，直接调用scrollTo，让View停留在特定的位置即可。需要注意的一点是，View往左滑动时，ScrollX的值是负的。
package com.nancyyihao.demo;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.text.TextPaint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Scroller;
public class RulerView extends View {
private static final String TAG = RulerView.class.getSimpleName() ;
private TextPaint mTextPaint;
private Paint mPaint ;
private int mWidth;
private int mHeight;
private int mPadding = 10;
private Scroller mScroller ;
private int mLastX;
private int mContentWidth = 1000;
private int mLineHeight = 50;
private int mFontHeight;
private int mFontWidth = 10;
private onValueChangedListener mValueChangedListener;
public interface onValueChangedListener {
void onValueChanged(int newValue);
}
public RulerView(Context context) {
super(context);
init(context);
}
public RulerView(Context context, AttributeSet attrs) {
super(context, attrs);
init(context);
}
public RulerView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(context);
}
public void setOnValueChangedListener(onValueChangedListener listener) {
this.mValueChangedListener = listener ;
}
private void init(Context context) {
mTextPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG | Paint.LINEAR_TEXT_FLAG);
mTextPaint.setTextAlign(Paint.Align.CENTER);
mTextPaint.setColor(Color.parseColor("#FF4081"));
mTextPaint.setTextSize(30);
mTextPaint.setStrokeWidth(2f);
Paint.FontMetrics fontMetrics = mTextPaint.getFontMetrics();
mFontHeight = Math.round(Math.abs(fontMetrics.top) + Math.abs(fontMetrics.bottom)) ;
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);
mPaint.setColor(Color.DKGRAY);
mPaint.setStrokeWidth(2f);
mPaint.setTextSize(30);
mPaint.setTextAlign(Paint.Align.CENTER);
//mScroller = new Scroller(context) ;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
mWidth = measureWidth(widthMeasureSpec);
mHeight = measureHeight(heightMeasureSpec);
setMeasuredDimension(mWidth , mHeight );
}
private int measureWidth(int widthMeasureSpec) {
int mode = MeasureSpec.getMode(widthMeasureSpec);
int size = MeasureSpec.getSize(widthMeasureSpec);
switch (mode) {
case MeasureSpec.EXACTLY:
return size ;
case MeasureSpec.AT_MOST:
int result = getPaddingLeft() + mContentWidth + getPaddingRight() ;
return Math.min(size, result) ;
}
return size ;
}
private int measureHeight(int heightMeasureSpec) {
int mode = MeasureSpec.getMode(heightMeasureSpec);
int size = MeasureSpec.getSize(heightMeasureSpec);
switch (mode) {
case MeasureSpec.EXACTLY:
return size ;
case MeasureSpec.AT_MOST:
return Math.min(size, mFontHeight + mLineHeight + 10 + mPadding) ;
}
return size ;
}
// private void smoothScrollTo(int destX, int destY) {
// int scrollX = getScrollX() ;
// int delta = destX - scrollX ;
// mScroller.startScroll(scrollX, 0, delta, 0 , 1000);
// invalidate();
// }
//
// @Override
// public void computeScroll() {
// super.computeScroll();
// if (mScroller.computeScrollOffset()) {
// smoothScrollTo(mScroller.getCurrX(), mScroller.getCurrY());
// postInvalidate();
//// ((View) getParent()).scrollTo(mScroller.getCurrX(),mScroller.getCurrY());
//// invalidate();
// }
// }
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
int startX = mPadding;
int stopX = mPadding;
int stopY =mHeight - mPadding;
for (int i = 0 ; i<=mContentWidth ; i += mFontWidth)
if (i % (mFontWidth *10) == 0) {
canvas.drawLine(startX + i, mFontHeight + mPadding + 5 , stopX + i, stopY, mTextPaint);
canvas.drawText(i + "", startX + i, mFontHeight + mPadding, mTextPaint);
} else if (i % mFontWidth == 0) {
canvas.drawLine(startX + i, mFontHeight + mPadding + 10, stopX + i, stopY, mPaint);
}
}
private int calcValue() {
return ( getCenter() + getScrollX() - mPadding) ; //minus startX
}
private int getCenter() {
return (getRight() - getLeft()) / 2 ;
}
@Override
public void scrollBy(int x, int y) {
super.scrollBy(x, y);
if (x < 0) { // drag to left
if (getScrollX() < -getCenter() + mPadding) {
scrollTo(-getCenter() + mPadding, 0);
}
} else
if (x >0) { // drag to right
if (mContentWidth - getScrollX() + x < getCenter()) {
scrollTo(mContentWidth - getCenter() + mFontWidth, 0);
}
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mLastX = (int) event.getX();
break;
case MotionEvent.ACTION_MOVE:
int x = (int) event.getX();
int deltaX = x - mLastX;
scrollBy(-deltaX, 0);
mLastX = x;
if (mValueChangedListener != null)
mValueChangedListener.onValueChanged(calcValue());
break;
}
return true;
}
}
整体上还是比较粗糙，原形虽然有了，但是还需要优化。
【Android】自定义View —— 滑动的次数选择器
android 滚轮刻度尺的实现
Android View自定义专题二(View滑动的实现)
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原文地址：http://www.cnblogs.com/jasonkent27/p/5836071.html
