如何将内容绑定到Xamarin.UWP中的其他内容中？

Question

我在一个页面中创建有其他控件的控件。我试图将一个框架的内容绑定到另一个绑定内容中，但是如果我第二次尝试访问它，它就会崩溃。

还尝试用相同的结果将绑定模式更改为TwoWay。

Xamarin形式: 5.0.0.2012

Xamarin.Essentials: 1.6.1

PropertyChanged.Fody: 3.3.2

Main Xaml ->

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:test="clr-namespace:Test"
             x:Class="Test.MainPage">
    <ContentPage.BindingContext>
        <test:MainViewModel/>
    </ContentPage.BindingContext>
    <StackLayout>
        <Button Text="Some Content View"
                Command="{Binding ChangeToContent}"/>
        <Button Text="Some other Content View"
                Command="{Binding ChangeToOtherContent}"
                />
        <Frame Content="{Binding model.MainContent}"/>
    </StackLayout>

</ContentPage>

MainViewModel-->

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Text;
using Xamarin.Forms;

namespace Test
{
    public class MainViewModel : INotifyPropertyChanged
    {
        public MainModel model { get; set; } = new MainModel();

        public Command ChangeToContent => new Command(() => {
            model.MainContent.Content = new Test1Content();
            });

        public Command ChangeToOtherContent => new Command(() => {
            model.MainContent.Content = new Test2Content();
        });



        #region INotifyPropertyChanged
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
        {
            var changed = PropertyChanged;
            if (changed == null)
                return;

            changed.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
        #endregion
    }
}

主要型号-->

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Text;
using Xamarin.Forms;

namespace Test
{
    public class MainModel : INotifyPropertyChanged
    {
        public Frame SomeContent { get; set; } = new Frame()
        {
            BackgroundColor = Color.Red,
            WidthRequest = 40,
            HeightRequest = 40
        };

        public Frame SomeOtherContent { get; set; } = new Frame()
         {
             BackgroundColor = Color.Blue,
             WidthRequest = 40,
             HeightRequest = 40
         };

        public ContentView MainContent { get; set; } = new ContentView();

        #region INotifyPropertyChanged
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
        {
            var changed = PropertyChanged;
            if (changed == null)
                return;

            changed.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
        #endregion
    }
}

第一内容视图-->

<?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="Test.Test1Content">
  <ContentView.Content>
      <StackLayout>
          <Label Text="This is Test 1 Content" />
            <Frame Content="{Binding model.SomeContent}"/>
        </StackLayout>
  </ContentView.Content>
</ContentView>

第二内容

<?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="Test.Test2Content">
  <ContentView.Content>
      <StackLayout>
          <Label Text="This is Test 2 Content" />
            <Frame Content="{Binding model.SomeOtherContent}"/>
        </StackLayout>
  </ContentView.Content>
</ContentView>

结果：https://imgur.com/a/caN9gxX

• 1图像是启动
• 2图像是在按下顶部按钮后
• 第3图像按下
• 4图像后的错误堆栈跟踪，再次按下顶部按钮后

F 225

Answer 1

我可能找到了解决办法。暗示出现在https://github.com/xamarin/Xamarin.Forms/issues/2713中。

如果我像这样修改视图模型中的命令ChangeToOtherContent和ChangeToContent：

        public Command ChangeToContent => new Command(() => {
            model.MainContent.Content = null;
            model.MainContent.Content = new Test1Content() { BindingContext = this };
            });

        public Command ChangeToOtherContent => new Command(() => {
            model.MainContent.Content = null;
            model.MainContent.Content = new Test2Content() { BindingContext = this };
        });

这个应用程序不会崩溃。

如果我连续触发命令，则空内容很重要。它可能会被bool取代，测试用户是否多次触发命令，但这意味着要进行更多的测试。

我不明白为什么需要添加绑定上下文，因为它在第一次呈现时是正确的。也许有人能再加进去。