如何使用代码更改android中的锁屏壁纸?

我可以更改主屏幕墙纸，但是我不能更改锁定屏幕墙纸，

                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);