Android 10.0 锁屏壁纸 LockscreenWallpaper

前言

一、设置壁纸

通过系统设置进行锁屏壁纸和桌面壁纸的设置。
Setting 部分的代码：
packages/apps/WallpaperPicker2/src/com/android/wallpaper/module/DefaultWallpaperPersister.java

    private int setStreamToWallpaperManagerCompat(InputStream inputStream, boolean allowBackup,
            int whichWallpaper) {
        try {
            // whichWallpaper  // 壁纸类型
            return mWallpaperManagerCompat.setStream(inputStream, null, allowBackup,
                    whichWallpaper);
        } catch (IOException e) {
            return 0;
        }
    }
  ...
//    int whichWallpaper;    // 壁纸类型
//    if (mDestination == DEST_HOME_SCREEN) {    // 桌面壁纸
//        whichWallpaper = WallpaperManagerCompat.FLAG_SYSTEM;
//    } else if (mDestination == DEST_LOCK_SCREEN) {  // 锁屏壁纸
//        whichWallpaper = WallpaperManagerCompat.FLAG_LOCK;
//    } else { // DEST_BOTH    // 桌面壁纸 和 锁屏壁纸
 //       whichWallpaper = WallpaperManagerCompat.FLAG_SYSTEM
//                | WallpaperManagerCompat.FLAG_LOCK;
//    }
  ...

mWallpaperManagerCompat 其实就是 WallpaperManagerCompatV16 的对象。
packages/apps/WallpaperPicker2/src/com/android/wallpaper/compat/WallpaperManagerCompatV16.java

    @Override
    public int setStream(InputStream data, Rect visibleCropHint, boolean allowBackup,
                         int whichWallpaper) throws IOException {
        mWallpaperManager.setStream(data);
        // Return a value greater than zero to indicate success.
        return 1;
    }

由此可知，壁纸的设置是通过 WallpaperManager 类来进行的。

二、锁屏壁纸的显示

锁屏壁纸显示流程图：

上面应用程序设置完成了，下面就该进行壁纸显示了。
WallpaperManager#setStream()
frameworks/base/core/java/android/app/WallpaperManager.java

    public int setStream(InputStream bitmapData, Rect visibleCropHint,
            boolean allowBackup, @SetWallpaperFlags int which)
                    throws IOException {
        // 省略部分代码......
        try {
            //sGlobals.mService即 WallpaperManagerService。
            // WallpaperManager 在 SystemServiceRegistry 实例化，
            // 过程中传入 WallpaperManagerService 的 binder 对象。   
            ParcelFileDescriptor fd = sGlobals.mService.setWallpaper(null,
                    mContext.getOpPackageName(), visibleCropHint, allowBackup,
                    result, which, completion, mContext.getUserId());
            if (fd != null) {
                FileOutputStream fos = null;
                try {
                    // 将壁纸copy一份并存储到对应目录，
                    // 默认是/data/system/users/0/wallpaper(或wallpaper_lock),
                    // 其中0是主用户的userId，支持多用户
                    fos = new ParcelFileDescriptor.AutoCloseOutputStream(fd);
                    copyStreamToWallpaperFile(bitmapData, fos);
                    fos.close();
                    completion.waitForCompletion();
                } finally {
                    IoUtils.closeQuietly(fos);
                }
            }
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
        return result.getInt(EXTRA_NEW_WALLPAPER_ID, 0);
    }

这里注意两个方法：sGlobals.mService.setWallpaper()和fos.close()。

先看第一个 WallpaperManagerService#setWallpaper() 方法：
frameworks/base/services/core/java/com/android/server/wallpaper/WallpaperManagerService.java

    public ParcelFileDescriptor setWallpaper(String name, String callingPackage,
            Rect cropHint, boolean allowBackup, Bundle extras, int which,
            IWallpaperManagerCallback completion, int userId) {
        userId = ActivityManager.handleIncomingUser(getCallingPid(), getCallingUid(), userId,
                false /* all */, true /* full */, "changing wallpaper", null /* pkg */);
        // 检查有没有设置壁纸的权限
       checkPermission(android.Manifest.permission.SET_WALLPAPER);
        
         //调用setStream方法的时候参数which必须是正确的
        if ((which & (FLAG_LOCK|FLAG_SYSTEM)) == 0) {
            final String msg = "Must specify a valid wallpaper category to set";
            Slog.e(TAG, msg);
            throw new IllegalArgumentException(msg);
        }
        // 省略部分代码......
        synchronized (mLock) {
            if (DEBUG) Slog.v(TAG, "setWallpaper which=0x" + Integer.toHexString(which));
            WallpaperData wallpaper;
  
            //如果当前没有锁屏壁纸的话，并且是设置桌面壁纸即which == FLAG_SYSTEM，那么同时设置为锁屏壁纸
            if (which == FLAG_SYSTEM && mLockWallpaperMap.get(userId) == null) {
                migrateSystemToLockWallpaperLocked(userId);
            }
            wallpaper = getWallpaperSafeLocked(userId, which);
            final long ident = Binder.clearCallingIdentity();
            try {
                // updateWallpaperBitmapLocked() 将创建一个文件描述符
                ParcelFileDescriptor pfd = updateWallpaperBitmapLocked(name, wallpaper, extras);
                if (pfd != null) {
                    wallpaper.imageWallpaperPending = true;
                    wallpaper.whichPending = which;
                    wallpaper.setComplete = completion;
                    wallpaper.cropHint.set(cropHint);
                    wallpaper.allowBackup = allowBackup;
                }
                return pfd;
            } finally {
                Binder.restoreCallingIdentity(ident);
            }
        }
    }

这里再跟进一步，看下 updateWallpaperBitmapLocked() 方法：
frameworks/base/services/core/java/com/android/server/wallpaper/WallpaperManagerService.java

    ParcelFileDescriptor updateWallpaperBitmapLocked(String name, WallpaperData wallpaper,
            Bundle extras) {
        if (name == null) name = "";
        try {
            // 通过getWallpaperDir() 获取文件路径；这个方法值得注意：后面会讲到。
            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);
            }
            // 创建一个文件描述符，并返回。
            ParcelFileDescriptor fd = ParcelFileDescriptor.open(wallpaper.wallpaperFile,
                    MODE_CREATE|MODE_READ_WRITE|MODE_TRUNCATE);
            // 省略部分代码......
            return fd;
        } catch (FileNotFoundException e) {
            Slog.w(TAG, "Error setting wallpaper", e);
        }
        return null;
    }

这里再看 fos.close() ，这个方法本身没什么可以看的，就是 FileOutputStream 文件字节输出流结束。但是这里涉及到了 WallpaperManagerService 的一个内部类 WallpaperObserver，通过名字我们就能知道它是一个观察者。
WallpaperObserver 初始化：在 WallpaperManagerService 初始化时，会调用 systemReady() 通过getWallpaperSafeLocked()方法初始化 WallpaperData，而这个 WallpaperData 中有个变量 wallpaperObserver ，也在开机时服务初始化， systemReady() 中调用 switchUser() 执行了 wallpaperObserver.startWatching()。
WallpaperObserver 这个内部类的作用：观察壁纸的变化并通知所有 IWallpaperServiceCallbacks 壁纸已经改变。 CREATE 在没有设置壁纸时触发，并且是第一次创建。每次更改壁纸时都会触发 CLOSE_WRITE，这也是关注 fos.close() 的原因。
所以文件的变化触发 WallpaperObserver 的 onEvent() ：
frameworks/base/services/core/java/com/android/server/wallpaper/WallpaperManagerService.java

        @Override
        public void onEvent(int event, String path) {
            if (path == null) {
                return;
            }
            final boolean moved = (event == MOVED_TO);
            final boolean written = (event == CLOSE_WRITE || moved);
            // 获取发生了 CLOSE_WRITE 事件的文件路径
            final File changedFile = new File(mWallpaperDir, path);
            // System and system+lock changes happen on the system wallpaper input file;
            // lock-only changes happen on the dedicated lock wallpaper input file
            // 用于判断事件是不是这个事件发生的。
            final boolean sysWallpaperChanged = (mWallpaperFile.equals(changedFile));
            final boolean lockWallpaperChanged = (mWallpaperLockFile.equals(changedFile));
            int notifyColorsWhich = 0;
            WallpaperData wallpaper = dataForEvent(sysWallpaperChanged, lockWallpaperChanged);
            // 如果是锁屏壁纸更新
            if (moved && lockWallpaperChanged) {
                SELinux.restorecon(changedFile);
                notifyLockWallpaperChanged();
                notifyWallpaperColorsChanged(wallpaper, FLAG_LOCK);
                return;
            }
            synchronized (mLock) {
                if (sysWallpaperChanged || lockWallpaperChanged) {
                    notifyCallbacksLocked(wallpaper);
                    if (wallpaper.wallpaperComponent == null
                            || event != CLOSE_WRITE // includes the MOVED_TO case
                            || wallpaper.imageWallpaperPending) {
                        if (written) {
                  
                            SELinux.restorecon(changedFile);
                            if (moved) {
                                loadSettingsLocked(wallpaper.userId, true);
                            }
                            generateCrop(wallpaper);
                          
                            wallpaper.imageWallpaperPending = false;
                            if (sysWallpaperChanged) {
                                // 桌面壁纸变化，那么bind ImageWallpaper，ImageWallpaper是负责显示静态桌面壁纸的
                               bindWallpaperComponentLocked(mImageWallpaper, true,
                                        false, wallpaper, null);
                                notifyColorsWhich |= FLAG_SYSTEM;
                            }
                            if (lockWallpaperChanged
                                    || (wallpaper.whichPending & FLAG_LOCK) != 0) {
                                if (DEBUG) {
                                    Slog.i(TAG, "Lock-relevant wallpaper changed");
                                }
                            
                                if (!lockWallpaperChanged) {
                                    //如果参数which是system+lock，也就是同时设置锁屏和桌面壁纸，那么remove锁屏壁纸，因为已经是同一张壁纸了
                                    mLockWallpaperMap.remove(wallpaper.userId);
                                }
                                // and in any case, tell keyguard about it
                                notifyLockWallpaperChanged();
                                notifyColorsWhich |= FLAG_LOCK;
                            }
                            saveSettingsLocked(wallpaper.userId);
                            // Publish completion *after* we've persisted the changes
                            if (wallpaper.setComplete != null) {
                                try {
                                    wallpaper.setComplete.onWallpaperChanged();
                                } catch (RemoteException e) {
                                    // if this fails we don't really care; the setting app may just
                                    // have crashed and that sort of thing is a fact of life.
                                }
                            }
                        }
                    }
                }
            }
            // Outside of the lock since it will synchronize itself
            if (notifyColorsWhich != 0) {
                notifyWallpaperColorsChanged(wallpaper, notifyColorsWhich);
            }
        }

先看锁屏壁纸更新这一部分 notifyLockWallpaperChanged() ：
frameworks/base/services/core/java/com/android/server/wallpaper/WallpaperManagerService.java

    private void notifyLockWallpaperChanged() {
        final IWallpaperManagerCallback cb = mKeyguardListener;
        if (cb != null) {
            try {
                cb.onWallpaperChanged();
            } catch (RemoteException e) {
                // Oh well it went away; no big deal
            }
        }
    }
    @Override
    public boolean setLockWallpaperCallback(IWallpaperManagerCallback cb) {
        checkPermission(android.Manifest.permission.INTERNAL_SYSTEM_WINDOW);
        synchronized (mLock) {
            mKeyguardListener = cb;
        }
        return true;
    }

notifyLockWallpaperChanged 中执行 cb.onWallpaperChanged()；这里的 cb = mKeyguardListener，而 mKeyguardListener 在 setLockWallpaperCallback() 方法中得到。 跟进我们发现 cb 其实就是 LockscreenWallpaper 引用，在 LockscreenWallpaper 的构造方法里赋值调用：
frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/LockscreenWallpaper.java

    @Inject
    public LockscreenWallpaper(WallpaperManager wallpaperManager,
            @Nullable IWallpaperManager iWallpaperManager,
            KeyguardUpdateMonitor keyguardUpdateMonitor,
            DumpManager dumpManager,
            NotificationMediaManager mediaManager,
            @Main Handler mainHandler) {
        // 省略部分代码......
        if (iWallpaperManager != null) {
            // Service is disabled on some devices like Automotive
            try {
                // iWallpaperManager 是 WallpaperManagerService 的 binder对象，
                // 通过 dagger 在 SystemServicesModule 实例化。
                iWallpaperManager.setLockWallpaperCallback(this);
            } catch (RemoteException e) {
                Log.e(TAG, "System dead?" + e);
            }
        }
    }

所以当锁屏壁纸更新时，就会回调到 LockscreenWallpaper#onWallpaperChanged() ：
frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/LockscreenWallpaper.java

    @Override
    public void onWallpaperChanged() {
        // Called on Binder thread.
        postUpdateWallpaper();
    }
    private void postUpdateWallpaper() {
        if (mH == null) {
            Log.wtfStack(TAG, "Trying to use LockscreenWallpaper before initialization.");
            return;
        }
        mH.removeCallbacks(this);
        mH.post(this);
    }

而 LockscreenWallpaper 类实现了 Runnable 接口的，所以看下它的 run() 方法； LockscreenWallpaper#run() ：
frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/LockscreenWallpaper.java

    @Override
    public void run() {
        // Called in response to onWallpaperChanged on the main thread.
        if (mLoader != null) {
            mLoader.cancel(false /* interrupt */);
        }
        final int currentUser = mCurrentUserId;
        final UserHandle selectedUser = mSelectedUser;
        mLoader = new AsyncTask<Void, Void, LoaderResult>() {
            @Override
            protected LoaderResult doInBackground(Void... params) {
                return loadBitmap(currentUser, selectedUser);
            }
            @Override
            protected void onPostExecute(LoaderResult result) {
                super.onPostExecute(result);
                if (isCancelled()) {
                    return;
                }
                if (result.success) {
                    mCached = true;
                    mCache = result.bitmap;
                    mUpdateMonitor.setHasLockscreenWallpaper(result.bitmap != null);
                    // 通知StatusBar更新壁纸
                    mMediaManager.updateMediaMetaData(
                            true /* metaDataChanged */, true /* allowEnterAnimation */);
                }
                mLoader = null;
            }
        }.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
    }

异步获取壁纸，并通知StatusBar去更新壁纸。
NotificationMediaManager#updateMediaMetaData()
frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/NotificationMediaManager.java

    public void updateMediaMetaData(boolean metaDataChanged, boolean allowEnterAnimation) {
        Trace.beginSection("StatusBar#updateMediaMetaData");
  
        // 省略部分代码......
        Bitmap artworkBitmap = null;
        if (mediaMetadata != null && !mKeyguardBypassController.getBypassEnabled()) {
            artworkBitmap = mediaMetadata.getBitmap(MediaMetadata.METADATA_KEY_ART);
            if (artworkBitmap == null) {
                artworkBitmap = mediaMetadata.getBitmap(MediaMetadata.METADATA_KEY_ALBUM_ART);
            }
        }
 
        //在后台线程上处理图稿并将生成的位图发送到finishUpdateMediaMetaData。
        if (metaDataChanged) {
            for (AsyncTask<?, ?, ?> task : mProcessArtworkTasks) {
                task.cancel(true);
            }
            mProcessArtworkTasks.clear();
        }
        if (artworkBitmap != null && !Utils.useQsMediaPlayer(mContext)) {
            mProcessArtworkTasks.add(new ProcessArtworkTask(this, metaDataChanged,
                    allowEnterAnimation).execute(artworkBitmap));
        } else {
            finishUpdateMediaMetaData(metaDataChanged, allowEnterAnimation, null);
        }
        Trace.endSection();
    }

对锁屏壁纸所在 view 做 setImageBitmap。
frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/NotificationMediaManager.java

    private void finishUpdateMediaMetaData(boolean metaDataChanged, boolean allowEnterAnimation,
            @Nullable Bitmap bmp) {
        Drawable artworkDrawable = null;
        if (bmp != null) {
            artworkDrawable = new BitmapDrawable(mBackdropBack.getResources(), bmp);
        }
        // 省略部分代码......
        if ((hasArtwork || DEBUG_MEDIA_FAKE_ARTWORK)
                && (mStatusBarStateController.getState() != StatusBarState.SHADE || allowWhenShade)
                &&  mBiometricUnlockController != null && mBiometricUnlockController.getMode()
                        != BiometricUnlockController.MODE_WAKE_AND_UNLOCK_PULSING
                && !hideBecauseOccluded) {
             // 省略部分代码......
            if (metaDataChanged) {
                if (mBackdropBack.getDrawable() != null) {
                    Drawable drawable =
                            mBackdropBack.getDrawable().getConstantState()
                                    .newDrawable(mBackdropFront.getResources()).mutate();
                    // 设置壁纸 setImageDrawable()
                    mBackdropFront.setImageDrawable(drawable);
                    mBackdropFront.setAlpha(1f);
                    mBackdropFront.setVisibility(View.VISIBLE);
                } else {
                    mBackdropFront.setVisibility(View.INVISIBLE);
                }
 
                if (DEBUG_MEDIA_FAKE_ARTWORK) {
                    final int c = 0xFF000000 | (int)(Math.random() * 0xFFFFFF);
                    Log.v(TAG, String.format("DEBUG_MEDIA: setting new color: 0x%08x", c));
                    mBackdropBack.setBackgroundColor(0xFFFFFFFF);
                    mBackdropBack.setImageDrawable(new ColorDrawable(c));
                } else {
                    mBackdropBack.setImageDrawable(artworkDrawable);
                }
 
                if (mBackdropFront.getVisibility() == View.VISIBLE) {
                    if (DEBUG_MEDIA) {
                        Log.v(TAG, "DEBUG_MEDIA: Crossfading album artwork from "
                                + mBackdropFront.getDrawable()
                                + " to "
                                + mBackdropBack.getDrawable());
                    }
                    mBackdropFront.animate()
                            .setDuration(250)
                            .alpha(0f).withEndAction(mHideBackdropFront);
                }
            }
        } else {
            // 省略部分代码......
        }
    }

通过 mBackdropFront.setImageDrawable(drawable) 方法将图片设置进去，完成锁屏壁纸的更新。
mBackdropFront 在 NotificationMediaManager的 setup() 方法被赋值，而 setup() 方法在 StatusBar 的 makeStatusBarView() 中被调用初始化。
StatusBar#makeStatusBarView()
frameworks/layoutlib/bridge/src/com/android/layoutlib/bridge/bars/StatusBar.java

    protected void makeStatusBarView(@Nullable RegisterStatusBarResult result) {
        // 省略部分代码......
        mMediaManager.setup(backdrop, backdrop.findViewById(R.id.backdrop_front),
                backdrop.findViewById(R.id.backdrop_back), mScrimController, mLockscreenWallpaper);
        // 省略部分代码......
    }