c# - 当我从 Listview 中选择项目以打开子页面时，iPhone 中没有任何反应。一切都在 android 设备中正常工作
问题描述
当我从列表视图中选择任何项目时，应该打开子页面。触发 listview onselecteditem 事件，但未打开子页面。
我正在使用 Xamarin 表单版本：3.3.0.967583 Visual Studio 2017
这是我的 ListView 绑定的 XAML 页面代码
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Grid Padding="8, 10 ,8, 5" BackgroundColor="#FFFFFF" HeightRequest="45" Margin="80, 0, 80, 0">
<Grid.RowDefinitions>
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="40" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="50" />
</Grid.ColumnDefinitions>
<RelativeLayout Grid.Row="0" Grid.Column="0" HeightRequest="40" WidthRequest="40">
<AbsoluteLayout HeightRequest="40" WidthRequest="40">
<Frame CornerRadius="{OnPlatform Android='40', iOS='20'}" BackgroundColor="#A9A9A9" HasShadow="False" OutlineColor="Transparent" BorderColor="Transparent" HeightRequest="40" WidthRequest="40" Padding="0" Margin="0" AbsoluteLayout.LayoutBounds="0, 0, 1, 1" AbsoluteLayout.LayoutFlags="All">
<Frame CornerRadius="{OnPlatform Android='40', iOS='20'}" BackgroundColor="#A9A9A9" HasShadow="False" OutlineColor="Transparent" BorderColor="Transparent" HeightRequest="40" WidthRequest="40" Padding="0" Margin="0">
<Image Source="Profile.png" Aspect="Fill" VerticalOptions="Center" HorizontalOptions="Center" BackgroundColor="Transparent" HeightRequest="40" WidthRequest="40" Margin="-1, -1, -1, -1"></Image>
</Frame>
</Frame>
</AbsoluteLayout>
<AbsoluteLayout HeightRequest="39" WidthRequest="39">
<Label Text="" FontSize="10" TextColor="{Binding IsOnline}"
AbsoluteLayout.LayoutFlags="All"
AbsoluteLayout.LayoutBounds="1, 1, 10, 10"
VerticalOptions="End" HorizontalOptions="End" >
<Label.FontFamily>
<OnPlatform x:TypeArguments="x:String"
Android="Font Awesome 5 Free-Solid-900.otf#Font Awesome 5 Free Solid"
iOS="FontAwesome5FreeSolid" />
</Label.FontFamily>
</Label>
</AbsoluteLayout>
</RelativeLayout>
<StackLayout Grid.Row="0" Grid.Column="1" VerticalOptions="CenterAndExpand" HeightRequest="30" Padding="2, 0, 0, 5">
<Label x:Name="UserName" Text="{Binding UserName}" FontSize="14" x:Uid="{Binding RoomName}" HorizontalOptions="Start" FontAttributes="Bold" TextColor="#000000" LineHeight="0" MaxLines="1" Margin="{OnPlatform Android='0, -3, 0, 0', iOS='0, -3, 0, 0'}" LineBreakMode="TailTruncation" HeightRequest="18" />
<Label Text="{Binding RequestStatus}" FontSize="12" HorizontalOptions="Start" VerticalOptions="Start" TextColor="{StaticResource lightGray}" LineHeight="0" MaxLines="1" Margin="{OnPlatform Android='0, -5, 0, 0', iOS='0, -5, 0, 0'}" LineBreakMode="TailTruncation" HeightRequest="18" />
</StackLayout>
<StackLayout Grid.Row="0" Grid.Column="2" VerticalOptions="Start" HorizontalOptions="End">
<Label FontSize="10" HorizontalOptions="End" TextColor="{Binding IsOnline}" Text="{Binding MessageTime}" LineHeight="1" Margin="{OnPlatform Android='0, 2, 0, 0', iOS='0, 0, 0, 0'}" />
<Grid Padding="0" Margin="0">
<Grid.RowDefinitions>
<RowDefinition Height="30" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="50" />
</Grid.ColumnDefinitions>
<Label Grid.Row="0" Grid.Column="0" Text="" IsVisible="{Binding IsAcceptDisplay}" FontSize="14"
TextColor="#2FB26C" HeightRequest="30" VerticalOptions="Center" WidthRequest="30" HorizontalOptions="End" HorizontalTextAlignment="End">
<Label.FontFamily>
<OnPlatform x:TypeArguments="x:String"
Android="Font Awesome 5 Free-Solid-900.otf#Font Awesome 5 Free Solid"
iOS="FontAwesome5FreeSolid" />
</Label.FontFamily>
</Label>
<StackLayout Grid.Row="0" Grid.Column="0" IsVisible="{Binding IsPendingMessageCount}" HorizontalOptions="End" Margin="14, 0, 0, 0">
<Frame VerticalOptions="Center" HorizontalOptions="End" WidthRequest="16" MinimumWidthRequest="16" HeightRequest="{OnPlatform Android='16', iOS='15'}"
OutlineColor="#2FB26C" BackgroundColor="#2FB26C" CornerRadius="{OnPlatform Android='20', iOS='8'}"
Margin="0, 0, 0, 0" Padding="{OnPlatform Android='0', iOS='0, 1, 0, 0'}" HasShadow="False">
<Label Text="{Binding PendingMessageCount}" FontSize="{OnPlatform Android='8', iOS='7'}" FontAttributes="Bold" VerticalOptions="CenterAndExpand" VerticalTextAlignment="Center"
TextColor="#FFFFFF" HorizontalOptions="Center" HorizontalTextAlignment="Center" HeightRequest="16" LineHeight="0.8"></Label>
</Frame>
</StackLayout>
</Grid>
</StackLayout>
</Grid>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
<ListView.Footer>
<StackLayout Orientation="Horizontal"></StackLayout>
</ListView.Footer>
</ListView>
</StackLayout>
</AbsoluteLayout>
</StackLayout>
下面是我管理 OnItemSelected 事件的 XAML.CS 页面
async void OnItemSelected(object sender, SelectedItemChangedEventArgs args)
{
try
{
var item = args.SelectedItem as User;
if (item == null)
return;
App.chatBoxPage = null;
App.chatBoxPage = new ChatBoxPage(new ChatViewModel(item));
await Navigation.PushAsync(App.chatBoxPage);
ChatList.SelectedItem = null;
}
catch (Exception e)
{
await DisplayAlert("Live Chat", "On Clicked : " + e.ToString(), "OK");
}
}
有时会引发以下异常
System.NullReferenceException: Object reference not set to an instance of an object
at Xamarin.Forms.VisualElement.get_BackgroundColor () <0x10178c450 + 0x00028> in <81ae0eb290e24f558e192928e3e37a57#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (TElement element) <0x1018a4620 + 0x000a3> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.iOS.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) <0x1018a4020 + 0x0003f> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) <0x10189cd70 + 0x0007b> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.OnChildAdded (Xamarin.Forms.VisualElement view) <0x1018a2a70 + 0x000af> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.Load () <0x1018a26e0 + 0x000ab> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (TElement element) <0x1018a4620 + 0x003c7> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.iOS.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) <0x1018a4020 + 0x0003f> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) <0x10189cd70 + 0x0007b> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.ListViewRenderer+UnevenListViewDataSource.CalculateHeightForCell (UIKit.UITableView tableView, Xamarin.Forms.Cell cell) <0x1018f0fe0 + 0x000b7> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.ListViewRenderer+UnevenListViewDataSource.GetEstimatedRowHeight (UIKit.UITableView table) <0x1018f0af0 + 0x0021b> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.ListViewRenderer.UpdateEstimatedRowHeight () <0x1018c0970 + 0x0010f> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.ListViewRenderer.OnElementChanged (Xamarin.Forms.Platform.iOS.ElementChangedEventArgs`1[TElement] e) <0x1018bf1a0 + 0x00b3b> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (TElement element) <0x1018a4620 + 0x004cb> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.iOS.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) <0x1018a4020 + 0x0003f> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) <0x10189cd70 + 0x0007b> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.OnChildAdded (Xamarin.Forms.VisualElement view) <0x1018a2a70 + 0x000af> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.Load () <0x1018a26e0 + 0x000ab> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (TElement element) <0x1018a4620 + 0x003c7> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.iOS.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) <0x1018a4020 + 0x0003f> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) <0x10189cd70 + 0x0007b> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.OnChildAdded (Xamarin.Forms.VisualElement view) <0x1018a2a70 + 0x000af> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.Load () <0x1018a26e0 + 0x000ab> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (TElement element) <0x1018a4620 + 0x003c7> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.iOS.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) <0x1018a4020 + 0x0003f> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) <0x10189cd70 + 0x0007b> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.OnChildAdded (Xamarin.Forms.VisualElement view) <0x1018a2a70 + 0x000af> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.Load () <0x1018a26e0 + 0x000ab> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].SetElement (TElement element) <0x1018a4620 + 0x003c7> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementRenderer`1[TElement].Xamarin.Forms.Platform.iOS.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) <0x1018a4020 + 0x0003f> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) <0x10189cd70 + 0x0007b> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.OnChildAdded (Xamarin.Forms.VisualElement view) <0x1018a2a70 + 0x000af> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.VisualElementPackager.Load () <0x1018a26e0 + 0x000ab> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.PageRenderer.ViewDidLoad () <0x1018c9b80 + 0x0034f> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at PSS_LiveChat.iOS.IosKeyboardFixPageRenderer.ViewDidLoad () <0x10089e900 + 0x0001b> in <39287061e96f454f92c45a96e90470c1#40b0903c179c66f2f42ecc37469bd36a>:0
at (wrapper managed-to-native) ObjCRuntime.Messaging.objc_msgSendSuper(intptr,intptr)
at UIKit.UIViewController.get_View () <0x10149e8c0 + 0x0006f> in <bbd12705940f4bb29392519af87b535b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.PageRenderer.get_NativeView () <0x1018c9630 + 0x00023> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.PageRenderer.SetElement (Xamarin.Forms.VisualElement element) <0x1018c9670 + 0x000ef> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) <0x10189cd70 + 0x0007b> in<85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.NavigationRenderer.CreateViewControllerForPage (Xamarin.Forms.Page page) <0x1018c5e10 + 0x00027> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
at Xamarin.Forms.Platform.iOS.NavigationRenderer+<OnPushAsync>d__51.MoveNext () <0x1018f95a0 + 0x0007b> in <85a5f025a15045539371e93897914a5b#40b0903c179c66f2f42ecc37469bd36a>:0
--- End of stack trace from previous location where exception was thrown ---
at Xamarin.Forms.NavigationPage+<PushAsyncInner>d__84.MoveNext () <0x10174c7f0 + 0x0023f> in <81ae0eb290e24f558e192928e3e37a57#40b0903c179c66f2f42ecc37469bd36a>:0
--- End of stack trace from previous location where exception was thrown ---
at Xamarin.Forms.NavigationPage+<PushAsync>d__55.MoveNext () <0x10174b730 + 0x00523> in <81ae0eb290e24f558e192928e3e37a57#40b0903c179c66f2f42ecc37469bd36a>:0
--- End of stack trace from previous location where exception was thrown ---
at PSS_LiveChat.Views.LiveChatPage+<OnItemSelected>d__5.MoveNext () <0x100cfb210 + 0x0040f> in <3b5956d19f5f4bdc84324069625851ef#40b0903c179c66f2f42ecc37469bd36a>:
解决方案
我觉得这样做的原因是您ItemSelected在应该使用事件时使用事件，因为如果您单击同一项目两次它不会ItemTapped触发，则只有在您选择新的项目时才会触发项目选择事件。Item
你ListView应该看起来像这样：
<ListView ItemTapped = "ListView_ItemTapped".../>
您在 cs 文件中的 ItemTapped 事件将如下所示：
private void ListView_ItemTapped(object sender, ItemTappedEventArgs e)
{
// Your code
}
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