Question

所以我在我的app中使用了这个ListView，它实例化了一次。 ListItem源是一个List，其中我是一个TemplateSelector，它根据列表中存储的对象类型显示不同的单元格。

如果我

我的问题就出现了

在列表中选择一行
弹出上一页
按我的列表
选择列表中的项目
崩溃。

我收到以下错误，

[MonoDroid] UNHANDLED EXCEPTION:
[MonoDroid] System.ArgumentException: 'jobject' must not be IntPtr.Zero.
[MonoDroid] Parameter name: jobject
[MonoDroid] at Android.Runtime.JNIEnv.CallIntMethod (intptr,intptr) [0x00010] in /Users/builder/data/lanes/1131/2a7b6821/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:343
[MonoDroid] at Android.Widget.AdapterView.get_FirstVisiblePosition () [0x00043] in /Users/builder/data/lanes/1131/2a7b6821/source/monodroid/src/Mono.Android/platforms/android-16/src/generated/Android.Widget.AdapterView.cs:866
[MonoDroid] at Xamarin.Forms.Platform.Android.ListViewAdapter.SelectItem (object) <IL 0x0001f, 0x00080>
[MonoDroid] at Xamarin.Forms.Platform.Android.ListViewAdapter.OnItemSelected (object,Xamarin.Forms.SelectedItemChangedEventArgs) <IL 0x00017, 0x00077>
[MonoDroid] at (wrapper delegate-invoke) System.EventHandler`1<Xamarin.Forms.SelectedItemChangedEventArgs>.invoke_void_object_TEventArgs (object,Xamarin.Forms.SelectedItemChangedEventArgs) <0x0007b>
[MonoDroid] at (wrapper delegate-invoke) System.EventHandler`1<Xamarin.Forms.SelectedItemChangedEventArgs>.invoke_void_object_TEventArgs (object,Xamarin.Forms.SelectedItemChangedEventArgs) <0x0003f>
[MonoDroid] at Xamarin.Forms.ListView.OnSelectedItemChanged (Xamarin.Forms.BindableObject,object,object) <IL 0x0001c, 0x000b7>
[MonoDroid] at Xamarin.Forms.BindableObject.SetValueActual (Xamarin.Forms.BindableProperty,object,bool,bool,bool) <IL 0x000b9, 0x0032e>
[MonoDroid] at Xamarin.Forms.BindableObject.SetValueCore (Xamarin.Forms.BindableProperty,object,bool,bool,bool) <IL 0x00213, 0x007b7>
[MonoDroid] at Xamarin.Forms.ListView.NotifyRowTapped (int,int) <IL 0x0004b, 0x0015b>
[MonoDroid] at Xamarin.Forms.ListView.NotifyRowTapped (int) <IL 0x0001c, 0x0009f>
[MonoDroid] at Xamarin.Forms.Platform.Android.ListViewAdapter.OnRealItemClicked (object,Android.Widget.AdapterView/ItemClickEventArgs) <IL 0x00025, 0x000bb>
[MonoDroid] at Android.Widget.AdapterView/IOnItemClickListenerImplementor.OnItemClick (Android.Widget.AdapterView,Android.Views.View,int,long) [0x0000d] in /Users/builder/data/lanes/1131/2a7b6821/source/monodroid/src/Mono.Android/platforms/android-16/src/generated/Android.Widget.AdapterView.cs:261
[MonoDroid] at Android.Widget.AdapterView/IOnItemClickListenerInvoker.n_OnItemClick_Landroid_widget_AdapterView_Landroid_view_View_IJ (intptr,intptr,intptr,intptr,int,long) [0x00019] in /Users/builder/data/lanes/1131/2a7b6821/source/monodroid/src/Mono.Android/platforms/android-16/src/generated/Android.Widget.AdapterView.cs:194
[MonoDroid] at (wrapper dynamic-method) object.09b491e2-61b2-4fd3-b387-65f476ed0dfb (intptr,intptr,intptr,intptr,int,long) <IL 0x00029, 0x00047>

有什么建议吗？适用于iOS！感谢。

Answer 1

我有同样的问题。如果您在ListView项目中使用切换，请尝试删除开关。当我移除Switch时，我的问题就消失了。

我不知道您的特定情况，但我用图像替换开关

 var image = new Image {
        HorizontalOptions = LayoutOptions.Start,
 };
 image.SetBinding( Image.SourceProperty, new Binding( "Image" ) );
 image.WidthRequest = image.HeightRequest = 15;

图像绑定到这些属性的位置：

public static ImageSource Checked = ImageSource.FromResource( "checked.png" );
public static ImageSource Unchecked = ImageSource.FromResource( "unchecked.png" );
public ImageSource Image {
    get {
        if ( Selected ) {
            return Checked;
        } else {
            return Unchecked;
        }
    }
}

private bool m_Selected;
public bool Selected { 
    get{ 
        return m_Selected;
    }
    set{
        SetField(ref m_Selected, value, "Selected");
        OnPropertyChanged( "Image" );
    }
}

OnPropertyChange和SetField来自INotifyPropertyChanged成员：

public class SomeClass : INotifyPropertyChanged {
    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged( string propertyName ) {
        PropertyChangedEventHandler handler = PropertyChanged;
        if ( handler != null ) handler( this, new PropertyChangedEventArgs( propertyName ) );
    }
    protected bool SetField<T>( ref T field, T value, string propertyName ) {
        if ( EqualityComparer<T>.Default.Equals( field, value ) ) return false;
        field = value;
        OnPropertyChanged( propertyName );
        return true;
    }
}

请注意如果Checked和Unchecked属性不是静态的，即使图像也会出现问题。

Answer 2

尝试在OnAppearing函数中添加所有控件，并在OnDisappearing中将Content设置为null，如下所示：

public class MyPage : ContentPage
{
   public MyPage()
   {
      Title = "MyPage";
   }

   protected override void OnAppearing()
   {
      List<string> listItems = new List<string> { "a", "b", "c" };
      ListView listView = new ListView
      {
         ItemsSource = listItems,
         ItemTemplate = new DataTemplate(() =>
         {
            TextCell textCell = new TextCell();
            textCell.SetBinding(TextCell.TextProperty, ".");
            return textCell;
         })
     };

     StackLayout stackLayout = new StackLayout();
     stackLayout.Children.Add(listView);
     Content = stackLayout;

     base.OnAppearing();
  }

   protected override void OnDisappearing()
   {
      Content = null;
      base.OnDisappearing();
   }
}

详细说明可在blog.cloush.com

上找到

Answer 3

我必须在我的案例中找到原因垃圾收集器帮我解决 await Task.Yield()是一个选项，有时它不起作用，在我的情况下它会在收集垃圾后解决

GC.collect();

在页面显示时删除缓存

Xamarin.forms Android ListView - ＆＃39; jobject＆＃39;不能是IntPtr.Zero

3 个答案: