Android中使用系統案頭背景作為應用背景，支援拖動

在Android應用開發中，使用系統案頭背景作為應用的背景，需要把應用的背景設定為透明背景，然後設定視窗的屬性為FLAG_SHOW_WALLPAPER即可顯示背景。

修改AndroidManifest.xml檔案裡面activity屬性：

        <activity android:name=".WallPaperTest"

                  android:label="@string/app_name"

                  android:theme="@android:style/Theme.Translucent">

然後在使用的時候，在onCreate裡面添加一個視窗屬性

getWindow().addFlags(WindowManager.LayoutParams.FLAG_SHOW_WALLPAPER);

在背景拖動的時候主要是使用了WallpaperManager這個類的兩個方法

public void setWallpaperOffsetSteps
(float xStep, float yStep)Since:
API Level 7

For applications that use multiple virtual screens showing a wallpaper, specify the step size between virtual screens. For example, if the launcher has 3 virtual screens, it would specify an xStep of 0.5, since the X offset for those screens are 0.0, 0.5
and 1.0

Parameters

xStep	The X offset delta from one screen to the next one
yStep	The Y offset delta from one screen to the next one

public void setWallpaperOffsets
(IBinder windowToken, float xOffset, float yOffset)Since:
API Level 5

Set the position of the current wallpaper within any larger space, when that wallpaper is visible behind the given window. The X and Y offsets are floating point numbers ranging from 0 to 1, representing where the wallpaper should be positioned within the
screen space. These only make sense when the wallpaper is larger than the screen.

Parameters

windowToken	The window who these offsets should be associated with, as returned by View.getWindowToken().
xOffset	The offset along the X dimension, from 0 to 1.
yOffset	The offset along the Y dimension, from 0 to 1. http://blog.csdn.net/yao_guet/article/details/6572739