将Launcher2主界面背景设为墙纸

将launcher2主界面设置为待机墙纸，现在只做到了和待机静态墙纸一致，动态的目前暂没有实现。可以在Launcher.java里的private void setWorkspaceBackground(boolean workspace) 函数里，增加如下代码：

        {
            View layout = mAppsCustomizeTabHost.getContent();    
            // 获取壁纸管理器  
            WallpaperManager wallpaperManager = WallpaperManager.getInstance(this);  
            // 获取当前壁纸  
            Drawable wallpaperDrawable = wallpaperManager.getDrawable();  
            // 将Drawable,转成Bitmap  
            Bitmap bm = ((BitmapDrawable) wallpaperDrawable).getBitmap();  

            // 需要详细说明一下，<span style="font-family: Arial, Helvetica, sans-serif;">pageCount</span><span style="font-family: Arial, Helvetica, sans-serif;">、getCurrentWorkspaceScreen()、ScreenWidth、ScreenHeight分别  </span>
            //对应于Launcher中的桌面屏幕总数、当前屏幕下标、屏幕宽度、屏幕高度.
            float step = 0;  
            DisplayMetrics dm = new DisplayMetrics();
            //获取屏幕信息
            getWindowManager().getDefaultDisplay().getMetrics(dm);
            int screenWidth = dm.widthPixels;
            int screenHeigh = dm.heightPixels;
            int pageCount;
            if (mWorkspace != null) 
            {
                pageCount =  mWorkspace.getPageCount();
            } 
            else 
            {
                pageCount = SCREEN_COUNT;
            }
            // 计算出屏幕的偏移量  
            step = (bm.getWidth() - screenWidth)/ (pageCount-1);  
            Log.d(TAG, "screenWidth="+screenWidth+";screenHeigh="+screenHeigh+";pageCount="+pageCount+";CurrentWorkspaceScreen="+getCurrentWorkspaceScreen());
            // 截取相应屏幕的Bitmap  
            Bitmap pbm = Bitmap.createBitmap(bm, (int)(getCurrentWorkspaceScreen()*step), 0,screenWidth,screenHeigh);  
            // 设置 背景  
            layout.setBackgroundDrawable(new BitmapDrawable(pbm));      
        }