Android7.0&8.0 默认壁纸修改

1.拷贝自定义壁纸
默认壁纸是default_wallpaper，在/frameworks/base/core/res下面。找到所以的default_wallpaper所在的地方，然后把我们自己的壁纸（custom_wallpaper.png）也拷贝到相应的地方。

2.修改默认壁纸
默认壁纸加载的地方在frameworks/base/core/java/android/app/WallpaperManager.java custom_wallpaper是我们自定义壁纸的图片名字（后面还需添加这个资源字段，否则编译失败，认不到）。

    /** * Open stream representing the default static image wallpaper. * * If the device defines no default wallpaper of the requested kind, * {@code null} is returned. * * @hide */
    public static InputStream openDefaultWallpaper(Context context, @SetWallpaperFlags int which) {
        final String whichProp;
        final int defaultResId;
        if (which == FLAG_LOCK) {
            /* Factory-default lock wallpapers are not yet supported whichProp = PROP_LOCK_WALLPAPER; defaultResId = com.android.internal.R.drawable.default_lock_wallpaper; */
            return null;
        } else {
            whichProp = PROP_WALLPAPER;
            //Aaron@20170711 F0017
            defaultResId = com.android.internal.R.drawable.custom_wallpaper;
            //defaultResId = com.android.internal.R.drawable.default_wallpaper;
        }
        final String path = SystemProperties.get(whichProp);
        if (!TextUtils.isEmpty(path)) {
            final File file = new File(path);
            if (file.exists()) {
                try {
                    return new FileInputStream(file);
                } catch (IOException e) {
                    // Ignored, fall back to platform default below
                }
            }
        }
        try {
            return context.getResources().openRawResource(defaultResId);
        } catch (NotFoundException e) {
            // no default defined for this device; this is not a failure
        }
        return null;
    }

3.声明资源
在frameworks中添加资源不是直接把图片拷贝过去就可以的，还需要给这个新添加的资源声明。frameworks/base/core/res/res/values/symbols.xml中添加新添加资源的字段。

  type="drawable" name="default_wallpaper" />
  type="drawable" name="custom_wallpaper" />
  type="drawable" name="default_lock_wallpaper" />