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我可以更改主屏幕壁纸，但我无法更改锁屏壁纸，
DisplayMetrics metrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(metrics);
// get the height and width of screen
int height = metrics.heightPixels;
int width = metrics.widthPixels;
WallpaperManager wallpaperManager = WallpaperManager
.getInstance(getApplicationContext());
wallpaperManager.setBitmap(bitmap);
wallpaperManager.suggestDesiredDimensions(width, height);