主要以在launcher界面长按点击wallpaper按钮来设置壁纸的流程。

当我们点击wallpaper按钮后进入WallpaperPickerActivity.java界面，分三块上为设置按钮，中为将要设置的wallpaper图片，下为所有壁纸的缩略图。

选择好壁纸后点击设置按钮

/packages/apps/Launcher3/WallpaperPicker/src/com/android/launcher3/WallpaperPickerActivity.java

// 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) {

// Ensure that a tile is slelected and loaded.

if (mSelectedTile != null && mCropView.getTileSource() != null) {

// Prevent user from selecting any new tile.

mWallpaperStrip.setVisibility(View.GONE);

actionBar.hide();

WallpaperTileInfo info = (WallpaperTileInfo) mSelectedTile.getTag();

info.onSave(WallpaperPickerActivity.this);//接着这个方法

} else {

// no tile was selected, so we just finish the activity and go back

setResult(Activity.RESULT_OK);

finish();

}

}

});

mSetWallpaperButton = findViewById(R.id.set_wallpaper_button);

上面这个方法调用FileWallpaperInfo中的onSave方法

 /packages/apps/Launcher3/WallpaperPicker/src/com/android/launcher3/WallpaperPickerActivity.java@FileWallpaperInfo @Override

public void onSave(WallpaperPickerActivity a)

{ a.setWallpaper(Uri.fromFile(mFile), true);//该setWallpaper在WallpaperCropActivity.java中实现

由上转入WallpaperCropActivity.java的setWallpaper()方法。

/packages/apps/Launcher3/WallpaperPicker/src/com/android/launcher3/WallpaperCropActivity.java

protected void setWallpaper(Uri uri, final boolean finishActivityWhenDone) {

int rotation = BitmapUtils.getRotationFromExif(getContext(), uri);

BitmapCropTask cropTask = new BitmapCropTask( getContext(), uri, null, rotation, 0, 0, true, false, null);//该task是图片处理与切割关键

final Point bounds = cropTask.getImageBounds();

Runnable onEndCrop = new Runnable() {

public void run() {

updateWallpaperDimensions(bounds.x, bounds.y);

if (finishActivityWhenDone) {

setResult(Activity.RESULT_OK);

finish();

} } };

cropTask.setCropSize(bounds.x, bounds.y);

cropTask.setOnEndRunnable(onEndCrop);

cropTask.setNoCrop(true);

cropTask.execute(); }

由上转入BitmapCropTask.java,具体代码就不全贴出，关键看cropBitmap()里的wallpaperManager.setStream(is);调用

/packages/apps/Launcher3/WallpaperPicker/src/com/android/gallery3d/common/BitmapCropTask.java

public boolean cropBitmap() {

boolean failure = false;

... ... ...

wallpaperManager.setStream(is);

... ... ...

}

我们看到最后通过流数据写入，将图片资源写入到wallpaper文件里面。具体实现我们转到wallpaperManager.java这个类

/frameworks/base/core/java/android/app/wallpaperManager.java

public void setStream(InputStream data) throws IOException {

if (sGlobals.mService == null) {

Log.w(TAG, "WallpaperService not running");

return;

}

try {

ParcelFileDescriptor fd = sGlobals.mService.setWallpaper(null,

mContext.getOpPackageName());//这个service调用是关键，获取wallpaper文件载体

if (fd == null) {

return;

}

FileOutputStream fos = null;

try {

fos = new ParcelFileDescriptor.AutoCloseOutputStream(fd);

setWallpaper(data, fos);//获取到wallpaper文件载体后往里面写如数据

} finally {

if (fos != null) {

fos.close();

}

}

} catch (RemoteException e) {

// Ignore

}

}

private void setWallpaper(InputStream data, FileOutputStream fos)//往wallpaper文件载体里面写数据

throws IOException {

byte[] buffer = new byte[32768];

int amt;

while ((amt=data.read(buffer)) > 0) {

fos.write(buffer, 0, amt);

}

}

我们看到上面有一个ParcelFileDescriptor fd = sGlobals.mService.setWallpaper(null,mContext.getOpPackageName());，该setWallpaper实现在WallpaperManagerService.java中实现,由于是远程service调用所以这里用到aidl.具体接口声明在

frameworks/base/core/java/android/app/IWallpaperManagerCallback.aidl，这里不列出。

public ParcelFileDescriptor setWallpaper(String name, String callingPackage) {

checkPermission(android.Manifest.permission.SET_WALLPAPER);

if (!isWallpaperSupported(callingPackage)) {

return null;

}

synchronized (mLock) {

if (DEBUG) Slog.v(TAG, "setWallpaper");

// /M: To support Smart Book @ {

if (isSmartBookSupport()) {

mHaveUsedSmartBook = false;

}

// /@ }

int userId = UserHandle.getCallingUserId();

WallpaperData wallpaper = getWallpaperSafeLocked(userId);

final long ident = Binder.clearCallingIdentity();

try {

ParcelFileDescriptor pfd = updateWallpaperBitmapLocked(name, wallpaper);

if (pfd != null) {

wallpaper.imageWallpaperPending = true;

}

return pfd;

} finally {

Binder.restoreCallingIdentity(ident);

}

}

}

ParcelFileDescriptor updateWallpaperBitmapLocked(String name, WallpaperData wallpaper) {

if (name == null) name = "";

try {

File dir = getWallpaperDir(wallpaper.userId);

if (!dir.exists()) {

dir.mkdir();

FileUtils.setPermissions(

dir.getPath(),

FileUtils.S_IRWXU|FileUtils.S_IRWXG|FileUtils.S_IXOTH,

-1, -1);

}

File file = new File(dir, mWallpaperFileName);

ParcelFileDescriptor fd = ParcelFileDescriptor.open(file,

MODE_CREATE|MODE_READ_WRITE|MODE_TRUNCATE);

if (!SELinux.restorecon(file)) {

return null;

}

wallpaper.name = name;

return fd;

} catch (FileNotFoundException e) {

Slog.w(TAG, "Error setting wallpaper", e);

}

return null;

}

private static File getWallpaperDir(int userId) {

return Environment.getUserSystemDirectory(userId);

}