android2.3 Launcher牆紙設置代碼追蹤

    case MENU_WALLPAPER_SETTINGS:              
         startWallpaper();//點擊壁紙設置菜單，會調用startWallpaper()  

  
    private void startWallpaper() {
        closeAllApps(true);
        final Intent pickWallpaper = new Intent(Intent.ACTION_SET_WALLPAPER);
        Intent chooser = Intent.createChooser(pickWallpaper,
        getText(R.string.chooser_wallpaper));
        startActivityForResult(chooser, REQUEST_PICK_WALLPAPER);
    }  //createChooser 會彈出一個對話框，把能處理Intent.ACTION_SET_WALLPAPER   
       //的activity都列出來供用戶選擇

選擇“壁紙”後會啓動Activity：WallpaperChooser

界面由三個View組成：ImageView 、Gallery、Button，

點擊Button後，設置壁紙：

    private void selectWallpaper(int position) {
        if (mIsWallpaperSet) {
            return;
        }

        mIsWallpaperSet = true;
        try {
            WallpaperManager wpm = (WallpaperManager)getSystemService(WALLPAPER_SERVICE);
            wpm.setResource(mImages.get(position));
            setResult(RESULT_OK);
            finish();
        } catch (IOException e) {
            Log.e(TAG, "Failed to set wallpaper: " + e);
        }
    }

Gallery的item被選擇後，ImageView會把相對應的大的圖片顯示出來，

此處通過異步處理類asynctask來完成的：

    public void onItemSelected(AdapterView parent, View v, int position, long id) {
        if (mLoader != null && mLoader.getStatus() != WallpaperLoader.Status.FINISHED) {
            mLoader.cancel();
        }
        mLoader = (WallpaperLoader) new WallpaperLoader().execute(position);
    }

其中execute的參數position就是AsyncTask的doInBackground後面的參數，

doInBackground  return的值，會作爲onPostExecute的參數

   

 class WallpaperLoader extends AsyncTask<Integer, Void, Bitmap> {
        BitmapFactory.Options mOptions;

        WallpaperLoader() {
            mOptions = new BitmapFactory.Options();
            mOptions.inDither = false;
            mOptions.inPreferredConfig = Bitmap.Config.ARGB_8888;            
        }
        
        protected Bitmap doInBackground(Integer... params)//此處params爲position
 {
            if (isCancelled()) return null;
            try {
                return BitmapFactory.decodeResource(getResources(),
                        mImages.get(params[0]), mOptions);
            } catch (OutOfMemoryError e) {
                Log.w(TAG, "Home no memory load current wallpaper", e);
                return null;
            }
        }

        @Override
        protected void onPostExecute(Bitmap b) //此處的b爲doInBackGround return的值
  {
            if (b == null) return;

            if (!isCancelled() && !mOptions.mCancel) {
                // Help the GC
                if (mBitmap != null) {
                    mBitmap.recycle();
                }
    
                final ImageView view = mImageView;
                view.setImageBitmap(b);
    
                mBitmap = b;
    
                final Drawable drawable = view.getDrawable();
                drawable.setFilterBitmap(true);
          //用來對Bitmap進行濾波處理，有抗鋸齒的效果 
                drawable.setDither(true);//防抖動
                view.postInvalidate();

                mLoader = null;
            } else {
               b.recycle(); 
            }
        }

        void cancel() {
            mOptions.requestCancelDecode();
            super.cancel(true);
        }
    }
}