判断是否为小屏幕设备

private double mScreenSize = 0.0;
private double getScreenSize(Context context) {
    if (mScreenSize == 0.0) {
        DisplayMetrics dm = new DisplayMetrics();
        ((Activity) context).getWindowManager().getDefaultDisplay().getMetrics(dm);
        double x = Math.pow(dm.widthPixels / dm.xdpi, 2);
        double y = Math.pow(dm.heightPixels / dm.ydpi, 2);
        mScreenSize  = Math.sqrt(x + y);
    }
    return mScreenSize;
}

getScreenSize(Context)<= 7.0 则为小屏幕设备