<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android"
    android:opacity="opaque">

    <item android:drawable="@color/black"/>

    <item>
        <bitmap android:src="@drawable/splash_bg" android:gravity="center"/>
    </item>
</layer-list>

注意：全屏的启动页建议使用.9图，否则使用 layer-list 显示效果仍然不佳。.9图文件大小过大，微信启动不设置 windowBackground ，通过设置 SplashActivity 的 ImageView scaletype 为 centerCrop 来适配

总结：
API <= 24(7.0) 使用 TYPE_TOAST 漏洞可以不用申请权限，直接显示
API >= 25(7.1.1) TYPE_TOAST 漏洞已修复，需要申请“允许显示在其他应用上层”权限，使用 TYPE_SYSTEM_ALERT
API >= 26(8.0) 系统将会限制 TYPE_TOAST 的使用，会直接抛出异常，使用 TYPE_APPLICATION_OVERLAY

实现：当手机开启导航栏时仍然全屏

 public WindowManager.LayoutParams getWindowParams() {
        WindowManager.LayoutParams layoutParams;
        if (!PermissionUtil.isOverMarshmallow()) {
            // < 6.0 使用 TYPE_TOST
            if (RomUtils.checkIsOppoRom()) {
                layoutParams = new WindowManager.LayoutParams(-1, -1, WindowManager.LayoutParams.TYPE_PRIORITY_PHONE, 263176, TRANSLUCENT);
            } else {
                layoutParams = new WindowManager.LayoutParams(-1, -1, WindowManager.LayoutParams.TYPE_TOAST, 263176, TRANSLUCENT);
            }
        } else {
            if (PermissionUtil.isOverO()) {
                // >= 8.0
                layoutParams =  new WindowManager.LayoutParams(-1, -1, WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY, 263176, TRANSLUCENT);
            } else {
                layoutParams = new WindowManager.LayoutParams(-1, -1, WindowManager.LayoutParams.TYPE_SYSTEM_ALERT, 263176, TRANSLUCENT);
            }
        }
        layoutParams.screenOrientation = ActivityInfo.SCREEN_ORIENTATION_PORTRAIT;
		//布局不受限制
        layoutParams.flags |= WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS;
        layoutParams.x = 0;
        layoutParams.y = 0;
        NoxApplication context = NoxApplication.getInstance();
        WindowManager mWm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        Display display = mWm.getDefaultDisplay();
        Point p = new Point();
        display.getRealSize(p);
        int statusHeight = ScreenUtil.getStatusHeight(NoxApplication.getInstance());
        Log.d("hj", "WindowPermissionHelper.getWindowParams: statusHeight:" + statusHeight);
        int navigationHeight = ScreenUtil.getNavigationHeight(NoxApplication.getInstance());
        Log.d("hj", "WindowPermissionHelper.getWindowParams: navigationHeight:" + navigationHeight);
        layoutParams.width = p.x;
        layoutParams.height = p.y + navigationHeight;
        Log.d("hj", "WindowPermissionHelper.getWindowParams: height:" + p.y);
        Log.d("hj", "WindowPermissionHelper.getWindowParams: width:" + p.x);
        return layoutParams;
    }

	
	View childAt = topBar.getChildAt(0);
    LinearLayout.LayoutParams layoutParams = (LinearLayout.LayoutParams) childAt.getLayoutParams();
    layoutParams.topMargin = ScreenUtil.getNavigationHeight(this);

注意：主要的限制在 FLAG_NOT_FOCUSABLE，WindowManager.LayoutParams.flags 中不能设置该 flag，否则监听不到返回键
可以使用：windowParams.flags &= ~FLAG_NOT_FOCUSABLE 消除该 flag