net maui 应用程序在从列表中基本删除时崩溃

Question

我是 .net Maui（和 Xamarin 表单）的新手，但我正在尝试从 https://www.youtube.com/watch?v=oNIvnCNzAqU

上的视频中获取 MVVM 工作示例

我的问题是，当我点击垃圾桶图标时，应用程序完全崩溃了。

这里是相关代码 TodoListViewModel.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;

namespace MauiApp1
{
  public class TodoListViewModel : BindableObject
  {

    public ObservableCollection<TodoItem> TodoItems { get; set; }


    public TodoListViewModel()
    {
      TodoItems = new ObservableCollection<TodoItem>
      {
        //test
        //new TodoItem("todo 1", false),
        //new TodoItem("todo 2", true),
        //new TodoItem("todo 3", false)
      };
    }

    string newTodoText = string.Empty;
    public string NewTodoText 
    {
      get { return newTodoText; }
      
      set
      {
        if (value == newTodoText) return;
        newTodoText = value;
        OnPropertyChanged();
      } 
    
    }

    public ICommand AddTodoCommand => new Command( AddTodoItem );
    public void AddTodoItem()
    {
      //Console.WriteLine(NewTodoText);
      TodoItems.Add(new TodoItem(NewTodoText, false));

      //clear entry and refocus
      NewTodoText = string.Empty;
      

      //Todo.Focus();

      ////dismiss keyboard
      //Todo.IsEnabled = false;
      //Todo.IsEnabled = true;
    }

    public ICommand RemoveTodoCommand => new Command( RemoveTodoItem );
    void RemoveTodoItem(Object o)
    {
      TodoItem todoItemBeingRemoved = o as TodoItem;
      TodoItems.Remove(todoItemBeingRemoved);
    }
  }
}

和 xaml MainPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:MauiApp1"
             x:Class="MauiApp1.MainPage"
             >

  <ContentPage.BindingContext>
    <local:TodoListViewModel />
  </ContentPage.BindingContext>

  <Grid RowDefinitions="Auto, Auto, Auto, *">

    <Entry
      Grid.Row="0"
      FontSize="24"
      Placeholder="Enter a ToDo"
      Text="{Binding NewTodoText}"
      ReturnCommand="{Binding AddTodoCommand}"
    />

    <Button 
        Grid.Row="1" 
        Margin="10"
        Padding="10"
        FontSize="24"
        Text="Add a Todo" 
        Command="{Binding AddTodoCommand}"
    />

    <ListView 
      Grid.Row="2"
      x:Name="TodoList" 
      ItemsSource="{Binding TodoItems}">

      <ListView.ItemTemplate>

        <DataTemplate>
          <ViewCell>
            
            <Grid 
              Margin="10, 0, 0, 0"
              
              ColumnDefinitions="auto, auto, *">
              <CheckBox 
                Grid.Column="0"
                  IsChecked="{Binding Complete}" />

              <Label 
                  Grid.Column="1" 
                  Text="{Binding TodoText}" 
                  FontSize="24" />

                <ImageButton 
                Grid.Column="2" 
                HorizontalOptions="End"  
                Source="delete.png" 
                Scale="0.7" 
                BackgroundColor="Transparent"
                Command="{Binding Path=BindingContext.RemoveTodoCommand, Source={x:Reference TodoList}}"
                CommandParameter="{Binding .}"/>
              
            </Grid>  

          </ViewCell>

        </DataTemplate>

      </ListView.ItemTemplate>

    </ListView>

  </Grid>

</ContentPage>

我试过调试它，ObservableCollections 似乎可以工作（为什么不可以，这是相当强大的技术）但是与 xaml 的链接似乎是失败的原因。

所以我添加了两个项目并删除了第一个，崩溃！这是直接 window:

输出的大量错误

> am start -a "android.intent.action.MAIN" -c "android.intent.category.LAUNCHER" -n "com.companyname.mauiapp1/crc64e632a077a20c694c.MainActivity"
> Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] cmp=com.companyname.mauiapp1/crc64e632a077a20c694c.MainActivity }
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/MauiApp1.dll
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/Mono.Android.dll [External]
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/System.Runtime.dll [External]
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/Java.Interop.dll [External]
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/System.Collections.dll [External]
Resolved pending breakpoint for 'Android.Runtime.JNIEnv.RegisterJniNatives(System.IntPtr, System.Int32, System.IntPtr, System.IntPtr, System.Int32)' to /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Android.Runtime/JNIEnv.cs:124 [0x00000].
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/System.Threading.dll [External]
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/System.Runtime.InteropServices.dll [External]
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/System.Threading.Thread.dll [External]
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/System.Diagnostics.StackTrace.dll [External]
Loaded assembly: data-0x756590c69030 [External]
Loaded assembly: data-0x756590c59020 [External]
Loaded assembly: data-0x75637a336040 [External]
Loaded assembly: data-0x756590c79040 [External]
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/netstandard.dll [External]
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/System.Linq.dll [External]
Loaded assembly: /data/data/com.companyname.mauiapp1/files/.__override__/System.Collections.Concurrent.dll [External]
Resolved pending breakpoint for 'Xamarin.HotReload.HotReloadAgent.BreakpointSendToIde(System.String)' to D:\a\_work\s\HotReload\Source\Xamarin.HotReload.Agent\HotReloadAgent.cs:419 [0x00000].

...删除了数百行

[nyname.mauiapp] runtime.cc:663]   at int androidx.recyclerview.widget.LinearLayoutManager.fill(androidx.recyclerview.widget.RecyclerView$Recycler, androidx.recyclerview.widget.LinearLayoutManager$LayoutState, androidx.recyclerview.widget.RecyclerView$State, boolean) (LinearLayoutManager.java:1591)
[nyname.mauiapp] runtime.cc:663]   at void androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(androidx.recyclerview.widget.RecyclerView$Recycler, androidx.recyclerview.widget.RecyclerView$State) (LinearLayoutManager.java:668)
[nyname.mauiapp] runtime.cc:663]   at void androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2() (RecyclerView.java:4309)
[nyname.mauiapp] runtime.cc:663]   at void androidx.recyclerview.widget.RecyclerView.dispatchLayout() (RecyclerView.java:4012)
[nyname.mauiapp] runtime.cc:663]   at void androidx.recyclerview.widget.RecyclerView.onLayout(boolean, int, int, int, int) (RecyclerView.java:4578)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void androidx.viewpager2.widget.ViewPager2.onLayout(boolean, int, int, int, int) (ViewPager2.java:527)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void com.google.android.material.appbar.HeaderScrollingViewBehavior.layoutChild(androidx.coordinatorlayout.widget.CoordinatorLayout, android.view.View, int) (HeaderScrollingViewBehavior.java:148)
[nyname.mauiapp] runtime.cc:663]   at boolean com.google.android.material.appbar.ViewOffsetBehavior.onLayoutChild(androidx.coordinatorlayout.widget.CoordinatorLayout, android.view.View, int) (ViewOffsetBehavior.java:43)
[nyname.mauiapp] runtime.cc:663]   at boolean com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior.onLayoutChild(androidx.coordinatorlayout.widget.CoordinatorLayout, android.view.View, int) (AppBarLayout.java:2122)
[nyname.mauiapp] runtime.cc:663]   at void androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(boolean, int, int, int, int) (CoordinatorLayout.java:953)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.layoutChildren(int, int, int, int, boolean) (FrameLayout.java:332)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.onLayout(boolean, int, int, int, int) (FrameLayout.java:270)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.LinearLayout.setChildFrame(android.view.View, int, int, int, int) (LinearLayout.java:1829)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.LinearLayout.layoutVertical(int, int, int, int) (LinearLayout.java:1673)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.LinearLayout.onLayout(boolean, int, int, int, int) (LinearLayout.java:1582)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.layoutChildren(int, int, int, int, boolean) (FrameLayout.java:332)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.onLayout(boolean, int, int, int, int) (FrameLayout.java:270)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void androidx.drawerlayout.widget.DrawerLayout.onLayout(boolean, int, int, int, int) (DrawerLayout.java:1263)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.LinearLayout.setChildFrame(android.view.View, int, int, int, int) (LinearLayout.java:1829)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.LinearLayout.layoutHorizontal(int, int, int, int) (LinearLayout.java:1818)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.LinearLayout.onLayout(boolean, int, int, int, int) (LinearLayout.java:1584)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.layoutChildren(int, int, int, int, boolean) (FrameLayout.java:332)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.onLayout(boolean, int, int, int, int) (FrameLayout.java:270)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.layoutChildren(int, int, int, int, boolean) (FrameLayout.java:332)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.onLayout(boolean, int, int, int, int) (FrameLayout.java:270)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.layoutChildren(int, int, int, int, boolean) (FrameLayout.java:332)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.onLayout(boolean, int, int, int, int) (FrameLayout.java:270)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.LinearLayout.setChildFrame(android.view.View, int, int, int, int) (LinearLayout.java:1829)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.LinearLayout.layoutVertical(int, int, int, int) (LinearLayout.java:1673)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.LinearLayout.onLayout(boolean, int, int, int, int) (LinearLayout.java:1582)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[nyname.mauiapp] runtime.cc:663]   at void android.view.ViewGroup.layout(int, int, int, int) (ViewGroup.java:6389)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.layoutChildren(int, int, int, int, boolean) (FrameLayout.java:332)
[nyname.mauiapp] runtime.cc:663]   at void android.widget.FrameLayout.onLayout(boolean, int, int, int, int) (FrameLayout.java:270)
[nyname.mauiapp] runtime.cc:663]   at void com.android.internal.policy.DecorView.onLayout(boolean, int, int, int, int) (DecorView.java:784)
[nyname.mauiapp] runtime.cc:663]   at void android.view.View.layout(int, int, int, int) (View.java:22844)
[libc] Fatal signal 6 (SIGABRT), code -1 (SI_QUEUE) in tid 31838 (nyname.mauiapp1), pid 31838 (nyname.mauiapp1)

告诉过你它很庞大，但我什么都想不通。我的意思是任何人都应该用这一切做什么！！！

这可能是一个非常常用的使用模式，但我无法弄清楚我做错了什么。感谢收到任何指示，希望这不是拼写错误...:sigh

G

Answer 1

ListView 是 4 个 "legacy" Renderer-based views 之一。

我建议改用 CollectionView。有些属性会有所不同，但在您的示例中，只需要进行两项更改：

将 ListView 更改为 CollectionView。
从 ItemTemplate 中删除 <ViewCell>。（或者会因“无法投射”异常而崩溃。）

        <CollectionView Grid.Row="2" x:Name="TodoList" ItemsSource="{Binding TodoItems}">
            <CollectionView.ItemTemplate>
                <DataTemplate>
                  <!-- REMOVED ViewCell -->
                    <Grid Margin="10, 0, 0, 0" ... />
                        ...
                    </Grid>
                </DataTemplate>
            </CollectionView.ItemTemplate>
        </CollectionView>

已验证此版本在 Android 上有效（删除第一项时不会崩溃）。

net maui 应用程序在从列表中基本删除时崩溃

net maui app crashes on basic delete from list

android

.net

mvvm

maui