在xamarin上做android布局时出错

Question

我试图制作一个上滑菜单，但我在布局中遇到错误。 我正在使用SlidingUpPanel组件。 （https://components.xamarin.com/view/slidinguppanel）

Axml代码：

<?xml version="1.0" encoding="utf-8"?>
<cheesebaron.slidinguppanel.SlidingUpPanelLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/sliding_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="bottom"
    app:collapsedHeight="68dp"
    app:shadowHeight="4dp"
    app:dragView="@+id/infobox">
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <Button
            android:text="Refresh"
            android:layout_width="124.0dp"
            android:layout_height="45.5dp"
            android:id="@+id/buttonRefresh"
            android:gravity="center" />
        <SeekBar
            android:layout_width="147.5dp"
            android:layout_height="wrap_content"
            android:id="@+id/seekBarRefresh"
            android:layout_gravity="end" />
        <TextView
            android:text="0"
            android:layout_width="133.0dp"
            android:layout_height="wrap_content"
            android:id="@+id/textViewValorSeekbar"
            android:gravity="center"
            android:layout_gravity="end" />
        <GridView
            android:minWidth="25px"
            android:minHeight="25px"
            android:layout_width="match_parent"
            android:layout_height="206.0dp"
            android:id="@+id/gridViewDados" />
        <ImageView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true" />
    </RelativeLayout>
</cheesebaron.slidinguppanel.SlidingUpPanelLayout>

错误：

Creating class loader with 20 projects

Creating LibraryClassLoader in shadow copy path C:\Users\User\AppData\Local\Temp\AndroidDesignerJars554604501710250253
Setting id 1 on newly created ClassLoader

Trying to load class md546c45d491b042b167774b8aaeb1a2ac0.SlidingUpPanelLayout

mono.android.DesignerException: System.NullReferenceException: Object reference not set to an instance of an object
    at mono.android.DesignerException.fromThrowable(DesignerException.java:46)
    at mono.android.DesignerSession.checkRenderResultForError(DesignerSession.java:187)
    at mono.android.DesignerSession.load(DesignerSession.java:239)
    at mono.android.DesignerSession.processMessage(DesignerSession.java:704)
    at mono.android.MessageListener.executeMessage(MessageListener.java:88)
    at mono.android.MessageListener$Runner.run(MessageListener.java:44)
    at java.lang.Thread.run(Thread.java:745)
Caused by: android.runtime.JavaProxyThrowable: System.NullReferenceException: Object reference not set to an instance of an object
  at Cheesebaron.SlidingUpPanel.SlidingUpPanelLayout.ComputeScroll () [0x00000] in C:\projects\slidinguppanel\src\SlidingUpPanel\SlidingUpPanelLayout.cs:647 
  at Android.Views.View.n_ComputeScroll (System.IntPtr jnienv, System.IntPtr native__this) [0x00008] in <33e6e739ac344166b157e323586f11a1>:0 
  at (wrapper dynamic-method) System.Object:8114d367-4bd0-42f5-918e-f697bfb6a11d (intptr,intptr)
    at md546c45d491b042b167774b8aaeb1a2ac0.SlidingUpPanelLayout.n_computeScroll(Native Method)
    at md546c45d491b042b167774b8aaeb1a2ac0.SlidingUpPanelLayout.computeScroll(SlidingUpPanelLayout.java:141)
    at android.view.View.draw(View.java:16850)
    at android.view.ViewGroup.drawChild_Original(ViewGroup.java:3764)
    at android.view.ViewGroup_Delegate.drawChild(ViewGroup_Delegate.java:61)
    at android.view.ViewGroup.drawChild(ViewGroup.java:3764)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3550)
    at android.view.View.draw(View.java:16977)
    at android.view.ViewGroup.drawChild_Original(ViewGroup.java:3764)
    at android.view.ViewGroup_Delegate.drawChild(ViewGroup_Delegate.java:61)
    at android.view.ViewGroup.drawChild(ViewGroup.java:3764)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3550)
    at android.view.View.draw(View.java:16977)
    at android.view.ViewGroup.drawChild_Original(ViewGroup.java:3764)
    at android.view.ViewGroup_Delegate.drawChild(ViewGroup_Delegate.java:61)
    at android.view.ViewGroup.drawChild(ViewGroup.java:3764)
    at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3550)
    at android.view.View.draw(View.java:17074)
    at com.android.layoutlib.bridge.impl.RenderSessionImpl.renderAndBuildResult(RenderSessionImpl.java:401)
    at com.android.layoutlib.bridge.impl.RenderSessionImpl.renderAndBuildResult(RenderSessionImpl.java:548)
    at com.android.layoutlib.bridge.impl.RenderSessionImpl.render(RenderSessionImpl.java:422)
    at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:434)
    at com.android.ide.common.rendering.LayoutLibrary.createSession(LayoutLibrary.java:368)
    at mono.android.DesignerSession.load(DesignerSession.java:233)
    ... 4 more

感谢大家提前。