Launcher3--壁纸

    public static abstract class WallpaperTileInfo {
        protected View mView;
        public Drawable mThumb;

        public void setView(View v) {
            mView = v;
        }
        public void onClick(WallpaperPickerActivity a) {}// 缩略图点击事件
        public void onSave(WallpaperPickerActivity a) {}// 设置壁纸，并做一些保存操作
        public void onDelete(WallpaperPickerActivity a) {}// 删除壁纸
        public boolean isSelectable() { return false; }// 是否可选
        public boolean isNamelessWallpaper() { return false; }// 壁纸是否没有名字
        public void onIndexUpdated(CharSequence label) {// 更新索引
            if (isNamelessWallpaper()) {
                mView.setContentDescription(label);
            }
        }
    }

PickImageInfo--图片选择器，在Activity中添加属性<action android:name="android.intent.action.GET_CONTENT" />，就可以隐式调用到，如图库

UriWallpaperInfo--通过图片的Uri来设置壁纸

FileWallpaperInfo--通过图片文件来设置壁纸

ResourceWallpaperInfo--Launcher3中内置的壁纸资源来设置

DefaultWallpaperInfo--系统默认壁纸，资源在framework中

<?xml version="1.0" encoding="utf-8"?><!--
/*
**
** 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.
*/
-->

<com.android.launcher3.WallpaperRootView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/wallpaper_root"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.android.launcher3.CropView
        android:id="@+id/cropView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <ProgressBar
        android:id="@+id/loading"
        style="@android:style/Widget.Holo.ProgressBar.Large"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:background="@android:color/transparent"
        android:indeterminate="true"
        android:indeterminateOnly="true"
        android:visibility="invisible" />

    <LinearLayout
        android:id="@+id/wallpaper_strip"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:orientation="vertical">

        <View
            android:layout_width="match_parent"
            android:layout_height="2dp"
            android:background="@drawable/tile_shadow_top" />

        <HorizontalScrollView
            android:id="@+id/wallpaper_scroll_container"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <LinearLayout
                android:id="@+id/master_wallpaper_list"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="horizontal">

                <LinearLayout
                    android:id="@+id/wallpaper_list"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="horizontal" />

                <LinearLayout
                    android:id="@+id/live_wallpaper_list"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="horizontal" />

                <LinearLayout
                    android:id="@+id/third_party_wallpaper_list"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:orientation="horizontal" />
            </LinearLayout>
        </HorizontalScrollView>

        <View
            android:layout_width="match_parent"
            android:layout_height="2dp"
            android:background="@drawable/tile_shadow_bottom" />
    </LinearLayout>
</com.android.launcher3.WallpaperRootView>

    WallpaperRootView是根视图，继承RelativeLayout自定义的一个视图，重写了fitSystemWindows方法，

    protected boolean fitSystemWindows(Rect insets) {
        a.setWallpaperStripYOffset(insets.bottom);
        return true;
    }

        setContentView(R.layout.wallpaper_picker);

        mCropView = (CropView) findViewById(R.id.cropView);
        mCropView.setVisibility(View.INVISIBLE);// 默认是不可见的

        mWallpaperStrip = findViewById(R.id.wallpaper_strip);

2)进度条--加载该界面时的进度条。

3)壁纸列表--LinearLayout布局块，其中的子视图HorizontalScrollView是一个横向的滑动视图，就是我们的壁纸列表，也是根据壁纸类型的分了多个布局块，分别加载。

    好像还少了ActionBar,这个是在代码中动态添加的，下面会说到。

        mCropView.setTouchCallback(new CropView.TouchCallback() {
            ViewPropertyAnimator mAnim;
            @Override
            public void onTouchDown() {
                if (mAnim != null) {
                    mAnim.cancel();
                }
                if (mWallpaperStrip.getAlpha() == 1f) {
                    mIgnoreNextTap = true;
                }
                mAnim = mWallpaperStrip.animate();
                mAnim.alpha(0f)
                    .setDuration(150)
                    .withEndAction(new Runnable() {
                        public void run() {
                            mWallpaperStrip.setVisibility(View.INVISIBLE);
                        }
                    });
                mAnim.setInterpolator(new AccelerateInterpolator(0.75f));
                mAnim.start();
            }
            @Override
            public void onTouchUp() {
                mIgnoreNextTap = false;
            }
            @Override
            public void onTap() {
                boolean ignoreTap = mIgnoreNextTap;
                mIgnoreNextTap = false;
                if (!ignoreTap) {
                    if (mAnim != null) {
                        mAnim.cancel();
                    }
                    mWallpaperStrip.setVisibility(View.VISIBLE);
                    mAnim = mWallpaperStrip.animate();
                    mAnim.alpha(1f)
                         .setDuration(150)
                         .setInterpolator(new DecelerateInterpolator(0.75f));
                    mAnim.start();
                }
            }
        });

    CropView的touch回调处理，这里只做了一些动画效果，具体裁剪的操作还是在CropView中实现的，这里就不详细说明了。

        mThumbnailOnClickListener = new OnClickListener() {
            public void onClick(View v) {
                if (mActionMode != null) {
                    // When CAB is up, clicking toggles the item instead
                    if (v.isLongClickable()) {
                        mLongClickListener.onLongClick(v);
                    }
                    return;
                }
                mSetWallpaperButton.setEnabled(true);
                WallpaperTileInfo info = (WallpaperTileInfo) v.getTag();
                if (info.isSelectable() && v.getVisibility() == View.VISIBLE) {
                    selectTile(v);
                }
                info.onClick(WallpaperPickerActivity.this);// 缩略图点击事件
            }
        };

    缩略图点击事件，如果处于ActionMode(长按事件)，处理长按事件，否则回调该壁纸所实现的onClick方法，启用mSetWallpaperButton，该控件定义在其父类WallpaperCropActivity中，
        // Action bar
        // Show the custom action bar view
        final ActionBar actionBar = getActionBar();
        actionBar.setCustomView(R.layout.actionbar_set_wallpaper);
        actionBar.getCustomView().setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        boolean finishActivityWhenDone = true;
                        cropImageAndSetWallpaper(imageUri, null, finishActivityWhenDone);
                    }
                });
        mSetWallpaperButton = findViewById(R.id.set_wallpaper_button);

        mLongClickListener = new View.OnLongClickListener() {
            // Called when the user long-clicks on someView
            public boolean onLongClick(View view) {
                CheckableFrameLayout c = (CheckableFrameLayout) view;
                c.toggle();
                if (mActionMode != null) {
                    mActionMode.invalidate();
                } else {
                    // Start the CAB using the ActionMode.Callback defined below
                    mActionMode = startActionMode(mActionModeCallback);
                    int childCount = mWallpapersView.getChildCount();
                    for (int i = 0; i < childCount; i++) {
                        mWallpapersView.getChildAt(i).setSelected(false);
                    }
                }
                return true;
            }
        };

    定义了缩略图长按事件，并不是所有的壁纸类型都设置了长按事件，下面会讲到。

        // Populate the built-in wallpapers
        // 填充内置壁纸，资源文件配置的壁纸和系统默认壁纸
        ArrayList<WallpaperTileInfo> wallpapers = findBundledWallpapers();
        mWallpapersView = (LinearLayout) findViewById(R.id.wallpaper_list);
        SimpleWallpapersAdapter ia = new SimpleWallpapersAdapter(this, wallpapers);
        populateWallpapersFromAdapter(mWallpapersView, ia, false);

    private ArrayList<WallpaperTileInfo> findBundledWallpapers() {
        final PackageManager pm = getPackageManager();
        final ArrayList<WallpaperTileInfo> bundled = new ArrayList<WallpaperTileInfo>(24);

        Partner partner = Partner.get(pm);
        if (partner != null) {
            final Resources partnerRes = partner.getResources();
            final int resId = partnerRes.getIdentifier(Partner.RES_WALLPAPERS, "array",
                    partner.getPackageName());
            if (resId != 0) {
                addWallpapers(bundled, partnerRes, partner.getPackageName(), resId);
            }

            // Add system wallpapers
            File systemDir = partner.getWallpaperDirectory();
            if (systemDir != null && systemDir.isDirectory()) {
                for (File file : systemDir.listFiles()) {
                    if (!file.isFile()) {
                        continue;
                    }
                    String name = file.getName();
                    int dotPos = name.lastIndexOf('.');
                    String extension = "";
                    if (dotPos >= -1) {
                        extension = name.substring(dotPos);
                        name = name.substring(0, dotPos);
                    }

                    if (name.endsWith("_small")) {
                        // it is a thumbnail
                        continue;
                    }

                    File thumbnail = new File(systemDir, name + "_small" + extension);
                    Bitmap thumb = BitmapFactory.decodeFile(thumbnail.getAbsolutePath());
                    if (thumb != null) {
                        bundled.add(new FileWallpaperInfo(file, new BitmapDrawable(thumb)));
                    }
                }
            }
        }

        // 添加Launcher中配置的壁纸
        Pair<ApplicationInfo, Integer> r = getWallpaperArrayResourceId();
        if (r != null) {
            try {
                Resources wallpaperRes = getPackageManager().getResourcesForApplication(r.first);
                addWallpapers(bundled, wallpaperRes, r.first.packageName, r.second);
            } catch (PackageManager.NameNotFoundException e) {
            }
        }

        // 创建一个空的实体，用于放置默认壁纸
        if (partner == null || !partner.hideDefaultWallpaper()) {
            // Add an entry for the default wallpaper (stored in system resources)
            WallpaperTileInfo defaultWallpaperInfo =
                    (Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT)
                    ? getPreKKDefaultWallpaperInfo()
                    : getDefaultWallpaper();
            if (defaultWallpaperInfo != null) {
                bundled.add(0, defaultWallpaperInfo);
            }
        }
        return bundled;
    }

<resources>
    <string-array name="wallpapers" translatable="false">
        <!-- This special drawable references the platform's private
             default_wallpaper resource so the user can always choose it. -->
        <item>zzz_wallpaper</item>
        <item>zzz_wallpaper_small</item>
        <!-- If you want additional bitmap drawable resources to appear in the
             wallpaper picker, add them to this list. For each foo.jpg be sure
             to include a foo_small.jpg to be used as a thumbnail in the
             scrolling gallery widget. -->
    </string-array>
</resources>

    private void populateWallpapersFromAdapter(ViewGroup parent, BaseAdapter adapter,
                                               boolean addLongPressHandler) {
        for (int i = 0; i < adapter.getCount(); i++) {
            FrameLayout thumbnail = (FrameLayout) adapter.getView(i, null, parent);
            parent.addView(thumbnail, i);
            WallpaperTileInfo info = (WallpaperTileInfo) adapter.getItem(i);
            thumbnail.setTag(info);
            info.setView(thumbnail);
            if (addLongPressHandler) {// 是否添加长按事件，只对数据库中保存的壁纸处理
                addLongPressHandler(thumbnail);
            }
            thumbnail.setOnClickListener(mThumbnailOnClickListener);
        }
    }