以编程方式制作屏幕截图并将其保存到SD卡

Question

如何以编程方式制作屏幕截图并将其保存到SD卡，我试过这个：

    View v = getWindow().getDecorView().getRootView();
    v.setDrawingCacheEnabled(true);
    Bitmap b = v.getDrawingCache();
    Util.saveBitmap(b, "snapshot", "screen");


class Util {
public static final int SDK_VERSION = getSdkVersion();

private static int getSdkVersion() {
    try {
        return Integer.parseInt(Build.VERSION.SDK);
    } catch (NumberFormatException e) {
        return 3;
    }
}

static String saveBitmap(Bitmap bitmap, String dir, String baseName) {
    try {
        File sdcard = Environment.getExternalStorageDirectory();
        File pictureDir = new File(sdcard, dir);
        pictureDir.mkdirs();
        File f = null;
        for (int i = 1; i < 200; ++i) {
            String name = baseName + i + ".png";
            f = new File(pictureDir, name);
            if (!f.exists()) {
                break;
            }
        }
        if (!f.exists()) {
            String name = f.getAbsolutePath();
            FileOutputStream fos = new FileOutputStream(name);
            bitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
            fos.flush();
            fos.close();
            return name;
        }
    } catch (Exception e) {
    } finally {
        /*
        if (fos != null) {
            fos.close();
        }
        */
    }
    return null;
}

static void bitmapBGRtoRGB(Bitmap bitmap, int width, int height) {
    int size = width * height;
    short data[] = new short[size];
    ShortBuffer buf = ShortBuffer.wrap(data);
    bitmap.copyPixelsToBuffer(buf);
    for (int i = 0; i < size; ++i) {
        //BGR-565 to RGB-565
        short v = data[i];
        data[i] = (short) (((v&0x1f) << 11) | (v&0x7e0) | ((v&0xf800) >> 11));
    }
    buf.rewind();
    bitmap.copyPixelsFromBuffer(buf);
}

}

但它不起作用