android - 为什么由服务制作的自定义视图没有 Decorview？

Question

我刚刚发现通过使用从服务制作的自定义视图WindowManager.LayoutParams没有DecorView.
这里是下面的代码

WindowManager mWindowManager = (WindowManager)getSystemService(WINDOW_SERVICE);
    
    WindowManager.LayoutParams  mParams = new WindowManager.LayoutParams(
            getDialogWidth(mWindowManager)
            , getDialogHeight(mWindowManager)
            , WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY
            , WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
            , PixelFormat.TRANSLUCENT);
    mParams.gravity = Gravity.CENTER;
    mParams.windowAnimations = android.R.style.Animation_Dialog;
    mWindowManager.addView(customView, mParams);

但是Activity, AlertDialog,DialogFragment等等都有一个DecorView.
为什么由服务制作的自定义视图没有 DecorView？

标签： androidandroid-layoutandroid-windowmanagerandroid-layoutparamsandroid-window