问题描述
工具:我正在使用 Xamarin 表单和 MVVM
我正在关注视频:https://www.youtube.com/watch?v=7mpe_1okwxk&list=PLwOF5UVsZWUiHY1CkRVjYJ6dm0iCvAlfw&index=12
NuGet:我已经安装了 NuGet > xamarin.community.toolkit
错误:
System.Reflection.TargetInvocationException: '调用的目标已抛出异常。'
您的应用已进入中断状态,但没有代码显示,因为所有线程都在执行外部代码(通常是系统或框架代码)。
调试:
我正在尝试将 Collection ItemSelect 事件转换为命令。我知道问题在于试图将事件转换为命令的代码,但我不确定如何调试此错误。由于应用程序已进入中断状态,我不能简单地添加断点。我在本主题的底部复制/粘贴了输出文件
请注意,如果我删除了将事件转换为命令的代码,它可以正常工作。所以这意味着问题在于:CollectionView.Behaviors
或 xct:ItemSelectedEventArgsConverter
查看页面
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="TestApp02_MVVM_Product.Views.ProductPage"
xmlns:xct="http://xamarin.com/schemas/2020/toolkit"
xmlns:android="clr-namespace:Xamarin.Forms.PlatformConfiguration.AndroidSpecific;assembly=Xamarin.Forms.Core">
<ContentPage.Resources>
<ResourceDictionary>
<xct:ItemSelectedEventArgsConverter x:Key="ItemSelectedEventArgsConverter" />
</ResourceDictionary>
</ContentPage.Resources>
<ContentPage.Content>
<CollectionView ItemsSource="{Binding ProductsList}"
SelectedItem="{Binding ItemSelectedEvent,Mode=TwoWay}"
...>
<!-- Turn Event Into Command-->
<CollectionView.Behaviors>
<xct:EventToCommandBehavior
EventName="ItemSelected"
Command="{Binding ItemSelectedCommand}"
EventArgsConverter="{StaticResource ItemSelectedEventArgsConverter}"/>
</CollectionView.Behaviors>
...
</CollectionView>
...
using System.ComponentModel;
using System.Runtime.CompilerServices;
using TestApp02_MVVM_Product.Models;
using Xamarin.CommunityToolkit.ObjectModel;
using Xamarin.Forms;
using System.Threading.Tasks;
namespace TestApp02_MVVM_Product.viewmodels
{
class Productviewmodel : INotifyPropertyChanged
{
public ObservableRangeCollection<ProductModel> ProductsList { get; set; }
public AsyncCommand<ProductModel> ItemSelectedCommand { get; }
public Productviewmodel()
{
ProductsList = new ObservableRangeCollection<ProductModel>();
ProductsList.Add(new ProductModel { ProductId = 1,ProductName = "Name 1",ProductDescription = "Description 1" });
ProductsList.Add(new ProductModel { ProductId = 1,ProductDescription = "Description 1" });
ItemSelectedCommand = new AsyncCommand<ProductModel>(OnItemSelectedCommand);
}//end of con
public ProductModel prevIoUsItemSelected;
public ProductModel currentItemSelected;
public ProductModel ItemSelectedEvent
{
get => currentItemSelected;
set
{
currentItemSelected = value;
OnPropertyChanged();
}
}
async Task OnItemSelectedCommand(ProductModel productModel)
{
if (productModel == null)
return;
await Application.Current.MainPage.displayAlert("Selected works","yayyy","Cancel");
}
...
#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
}
}
** 输出 **
[Mono] DllImport searching in: '__Internal' ('(null)').
[Mono] Searching for 'java_interop_jnienv_new_object_array'.
[Mono] Probing 'java_interop_jnienv_new_object_array'.
[Mono] Found as 'java_interop_jnienv_new_object_array'.
[Mono] DllImport searching in: '__Internal' ('(null)').
[Mono] Searching for 'java_interop_jnienv_set_object_array_element'.
[Mono] Probing 'java_interop_jnienv_set_object_array_element'.
[Mono] Found as 'java_interop_jnienv_set_object_array_element'.
[Mono] DllImport searching in: '__Internal' ('(null)').
[Mono] Searching for 'java_interop_jnienv_is_assignable_from'.
[Mono] Probing 'java_interop_jnienv_is_assignable_from'.
[Mono] Found as 'java_interop_jnienv_is_assignable_from'.
[Mono] DllImport searching in: '__Internal' ('(null)').
[Mono] Searching for 'java_interop_jnienv_new_float_array'.
[Mono] Probing 'java_interop_jnienv_new_float_array'.
[Mono] Found as 'java_interop_jnienv_new_float_array'.
[Mono] DllImport searching in: '__Internal' ('(null)').
[Mono] Searching for 'java_interop_jnienv_set_float_array_region'.
[Mono] Probing 'java_interop_jnienv_set_float_array_region'.
[Mono] Found as 'java_interop_jnienv_set_float_array_region'.
[Mono] DllImport searching in: '__Internal' ('(null)').
[Mono] Searching for 'java_interop_jnienv_get_float_array_region'.
[Mono] Probing 'java_interop_jnienv_get_float_array_region'.
[Mono] Found as 'java_interop_jnienv_get_float_array_region'.
[Mono] DllImport searching in: '__Internal' ('(null)').
[Mono] Searching for 'java_interop_jnienv_call_float_method_a'.
[Mono] Probing 'java_interop_jnienv_call_float_method_a'.
[Mono] Found as 'java_interop_jnienv_call_float_method_a'.
[Mono] DllImport searching in: '__Internal' ('(null)').
[Mono] Searching for 'java_interop_jnienv_new_local_ref'.
[Mono] Probing 'java_interop_jnienv_new_local_ref'.
[Mono] Found as 'java_interop_jnienv_new_local_ref'.
[Mono] Requesting loading reference 11 (of 12) of /data/data/com.companyname.testapp02_mvvm_product/files/.__override__/Xamarin.AndroidX.Fragment.dll
[Mono] Loading reference 11 of /data/data/com.companyname.testapp02_mvvm_product/files/.__override__/Xamarin.AndroidX.Fragment.dll asmctx DEFAULT,looking for Xamarin.AndroidX.ViewPager,Version=1.0.0.0,Culture=neutral,PublicKeyToken=null
[Mono] Assembly Ref addref Xamarin.AndroidX.Fragment[0x793c9b6900] -> Xamarin.AndroidX.ViewPager[0x793c9f8300]: 3
[Mono] Requesting loading reference 12 (of 15) of /data/data/com.companyname.testapp02_mvvm_product/files/.__override__/Xamarin.Google.Android.Material.dll
[Mono] Loading reference 12 of /data/data/com.companyname.testapp02_mvvm_product/files/.__override__/Xamarin.Google.Android.Material.dll asmctx DEFAULT,PublicKeyToken=null
[Mono] Assembly Ref addref Xamarin.Google.Android.Material[0x793c9f8b00] -> Xamarin.AndroidX.ViewPager[0x793c9f8300]: 4
[TabLayout] MODE_SCROLLABLE + GraviTY_FILL is not supported,GraviTY_START will be used instead
[Mono] Requesting loading reference 4 (of 11) of /data/data/com.companyname.testapp02_mvvm_product/files/.__override__/Xamarin.CommunityToolkit.dll
[Mono] Loading reference 4 of /data/data/com.companyname.testapp02_mvvm_product/files/.__override__/Xamarin.CommunityToolkit.dll asmctx DEFAULT,looking for System,Version=2.0.5.0,PublicKeyToken=7cec85d7bea7798e
[Mono] Assembly Ref addref Xamarin.CommunityToolkit[0x793c9f8500] -> System[0x794c9eb480]: 9
[Mono] Requesting loading reference 9 (of 11) of /data/data/com.companyname.testapp02_mvvm_product/files/.__override__/Xamarin.CommunityToolkit.dll
[Mono] Loading reference 9 of /data/data/com.companyname.testapp02_mvvm_product/files/.__override__/Xamarin.CommunityToolkit.dll asmctx DEFAULT,looking for System.Core,PublicKeyToken=7cec85d7bea7798e
[Mono] Assembly Ref addref Xamarin.CommunityToolkit[0x793c9f8500] -> System.Core[0x793c887980]: 5
[Mono] DllImport searching in: '__Internal' ('(null)').
[Mono] Searching for 'java_interop_jnienv_throw'.
[Mono] Probing 'java_interop_jnienv_throw'.
[Mono] Found as 'java_interop_jnienv_throw'.
**System.Reflection.TargetInvocationException:** 'Exception has been thrown by the target of an invocation.'
解决方法
我把 ListView 和 CollectionView 混在一起了。 CollectionView 已经有内置的 SelectionChangedCommand 所以不需要
以下代码对我有用
查看
<CollectionView ItemsSource="{Binding ProductsList}"
SelectedItem="{Binding ItemSelectedEvent,Mode=TwoWay}"
SelectionChangedCommand="{Binding SelectionChangedCommand}">
ViewModel
public AsyncCommand<ProductModel> SelectionChangedCommand { get; }
...
SelectionChangedCommand = new AsyncCommand<ProductModel>(OnSelectionChangedCommand);
async Task OnSelectionChangedCommand(ProductModel productModel)
{
//item is not selected so do nothing
if (productModel == null)
return;
//item is selcted so do logic here
await Application.Current.MainPage.DisplayAlert("Selected works","yayyy","Cancel");
}