Xamarin.Forms MasterDetail页面NavBar定制

对于Xamarin.Forms中的MasterDetail页面问题，我需要大量帮助。

我想做的就是非常简单地自定义NavigationBar的背景以使用渐变。我的设置是带有Prism的Xamarin.Forms应用程序，在该应用程序中，我首先登录用户，然后导航至如下页面：MasterDetail

await NavigationService.NavigateAsync("MyMasterDetailPage/NavigationPage/MyDetailPage")

我遇到的问题是，无论我做什么我都不能改变它的颜色NavigationBar。

我已经尝试了CustomRenderers（目前适用于Android）的几种不同变体，以及仅在PCL项目TitleView的Detail页面中添加了自定义项。我还尝试过更改styles.xml文件，更改ToolBar.axml以使用我制作的可绘制对象，但到目前为止我仍然没有运气。

非常感谢您的帮助，因为我在此问题上苦苦挣扎了几天。

以下是发生的情况的屏幕截图：

Toolbar.axml：

<android.support.v7.widget.Toolbar
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
android:popupTheme="@style/ThemeOverlay.AppCompat.Light"
android:background="@drawable/gradient_background_drawable"
 />

styles.xml：

<?xml version="1.0" encoding="utf-8" ?>
<resources>

  <style name="MainTheme" parent="MainTheme.Base">
  </style>
  <!-- Base theme applied no matter what API -->
  <style name="MainTheme.Base" parent="Theme.AppCompat.Light.DarkActionBar">
    <!--If you are using revision 22.1 please use just windowNoTitle. Without android:-->
    <item name="windowNoTitle">true</item>
    <!--We will be using the toolbar so no need to show ActionBar-->
    <item name="windowActionBar">false</item>
    <!-- Set theme colors from http://www.google.com/design/spec/style/color.html#color-color-palette -->
    <!-- colorPrimary is used for the default action bar background -->
    <item name="colorPrimary">#89D362</item>
    <!-- colorPrimaryDark is used for the status bar -->
    <item name="colorPrimaryDark">#89D362</item>
    <!-- colorAccent is used as the default value for colorControlActivated
         which is used to tint widgets -->
    <item name="colorAccent">#FF4081</item>
    <!-- You can also set colorControlNormal, colorControlActivated
         colorControlHighlight and colorSwitchThumbNormal. -->
    <!--<item name="windowActionModeOverlay">true</item>-->

    <item name="android:datePickerDialogTheme">@style/AppCompatDialogStyle</item>
    <item name="drawerArrowStyle">@style/DrawerArrowStyle</item>
  </style>

  <style name="AppCompatDialogStyle" parent="Theme.AppCompat.Light.Dialog">
    <item name="colorAccent">#FF4081</item>
  </style>

  <style name="DrawerArrowStyle" parent="@style/Widget.AppCompat.DrawerArrowToggle">
    <item name="spinBars">true</item>
    <item name="color">#89D362</item>
  </style>
</resources>

gradient_background_drawable：

<?xml version="1.0" encoding="utf-8" ?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
  <gradient android:type="linear"
            android:angle="270"
            android:startColor="#000E0E"
            android:endColor="#3D3939">
  </gradient>

</shape>

MasterDetailPageRenderer：

protected override void OnLayout(bool changed, int l, int t, int r, int b)
        {
            base.OnLayout(changed, l, t, r, b);
            var toolbar = FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
            if (toolbar != null)
            {
                for (int i = 0; i < toolbar.ChildCount; i++)
                {
                    var child = toolbar.GetChildAt(i);
                    child.Background = Context.GetDrawable(Resource.Drawable.gradient_background_drawable);
                }

                toolbar.Background = Context.GetDrawable(Resource.Drawable.gradient_background_drawable);
            }
        }

NavigationPageRenderer：

protected override void OnElementChanged(ElementChangedEventArgs<NavigationPage> e)
        {
            base.OnElementChanged(e);
            if (e.OldElement != null || Element == null)
            {
                return;
            }

            var actionBar = ((FormsAppCompatActivity)Context).SupportActionBar;
            actionBar.SetBackgroundDrawable(Context.GetDrawable(Resource.Drawable.gradient_background_drawable));
        }

        protected override void OnLayout(bool changed, int l, int t, int r, int b)
        {
            base.OnLayout(changed, l, t, r, b);
            var toolbar = FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
            if (toolbar != null)
            {
                //for (int i = 0; i < toolbar.ChildCount; i++)
                //{
                //    var child = toolbar.GetChildAt(i);
                //    child.Background = Context.GetDrawable(Resource.Drawable.gradient_background_drawable);
                //}

                toolbar.Background = Context.GetDrawable(Resource.Drawable.gradient_background_drawable);
            }
        }

        public override void OnViewAdded(Android.Views.View child)
        {
            base.OnViewAdded(child);
            if (child.GetType() == typeof(Android.Support.V7.Widget.Toolbar))
            {
                _toolbar = (Android.Support.V7.Widget.Toolbar)child;

                _toolbar.Background = Context.GetDrawable(Resource.Drawable.gradient_background_drawable);
            }
        }