[英]MessagingCenter not subscribing
我是 Xamarin 的新手(通常是編碼新手)。
我在ListView
中使用xct TouchEffect
來嘗試獲取 LongPress 菜單。
由於TouchEffect.LongPressCommand
是一個命令,我只能將它綁定到 model 頁面。 所以......我正在嘗試通過MessagingCenter
將信息發送到代碼隱藏。
我遇到的問題是消息沒有收到。
我讀了很多書並試圖弄清楚,我想為了能夠接收到消息,訂閱者需要先實例化/初始化。
我遇到的主要問題是......我不知道該怎么做,哈哈。
還是我想做的整件事都是錯的?
我將添加一些代碼,但如果需要其他任何內容,請告訴我。
注意:加載頁面(當應用程序啟動時)是一個 GroupPage(工作正常),問題出在 ItemsPage。
非常感謝大家。
項目頁面.xaml
<ContentPage.BindingContext>
<localvm:ItemViewModel/>
</ContentPage.BindingContext>
<ListView ItemsSource="{Binding Items, Mode=TwoWay}" x:Name="lstView"
AbsoluteLayout.LayoutBounds="0,0,1,1"
AbsoluteLayout.LayoutFlags="All"
SelectedItem="{Binding SelectedItem}" HasUnevenRows="True" RowHeight="50">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Grid Padding="0,0,8,0" Margin="4,0,4,0" xct:TouchEffect.LongPressCommand="{Binding LongPressItemCommand}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="7*"/>
</Grid.ColumnDefinitions>
<Label Text="{Binding ItemName}" TextColor="Black" Grid.Column="1" FontSize="Medium"></Label>
<Label Text="{Binding ItemDescription}" Grid.Column="1" VerticalTextAlignment="End"/>
</Grid>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
項目頁面.cs
namespace MobileApp2
{
public partial class ItemsPage : ContentPage
{
public ItemsPage()
{
InitializeComponent();
MessagingCenter.Subscribe<Item, Guid>(this, "PopupMenuItemMsg",
(page, itemId) =>
{
Main_PopupMenu(itemId);
});
}
public async void Main_PopupMenu(Guid itemId)
{
DisplayActionSheet("Test", "Test", "OK");
}
}
}
Items.cs (模型)
namespace MobileApp2
{
public class Item : INotifyPropertyChanged
{
public Command LongPressItemCommand { get; }
public Guid ItemId { get; set; }
public Guid GroupId { get; set; }
private string itemName = string.Empty;
public string ItemName
{
get { return itemName; }
set
{
if (value != null) itemName = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("ItemName"));
}
}
private string itemDescription = string.Empty;
public string ItemDescription
{
get
{
return itemDescription.Trim();
}
set
{
if (value != null) itemDescription = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("ItemDescription"));
}
}
public Item(string itemName, string itemDescription)
{
ItemName = itemName;
ItemDescription = itemDescription;
}
public Item()
{
LongPressItemCommand = new Command(() =>
{
MessagingCenter.Send<Item, Guid>(this, "PopupMenuItemMsg", ItemId);
});
}
public event PropertyChangedEventHandler PropertyChanged;
}
}
您可以使用 Command 的相對綁定檢查下面的代碼。
Model:
public class Item
{
public string ItemName { get; set; }
public string ItemDescription { get; set; }
}
視圖模型:
public class ItemViewModel
{
public ICommand LongPressItemCommand { get; set; }
public Guid ItemId { get; set; }
public ObservableCollection<Item> Items { get; set; }
public ItemViewModel()
{
LongPressItemCommand = new Command(() =>
{
MessagingCenter.Send<ItemViewModel, Guid>(this, "PopupMenuItemMsg", ItemId);
});
CreateCollection();
}
public void LongPress()
{
}
public void CreateCollection()
{
Items = new ObservableCollection<Item>()
{
new Item(){ ItemName="A", ItemDescription="AA"},
new Item(){ ItemName="B", ItemDescription="BB"},
new Item(){ ItemName="C", ItemDescription="CC"},
};
}
}
Xaml:
<ContentPage.BindingContext>
<localvm:ItemViewModel></localvm:ItemViewModel>
</ContentPage.BindingContext>
<StackLayout>
<ListView ItemsSource="{Binding Items, Mode=TwoWay}" x:Name="lstView"
AbsoluteLayout.LayoutBounds="0,0,1,1"
AbsoluteLayout.LayoutFlags="All"
SelectedItem="{Binding SelectedItem}" HasUnevenRows="True" RowHeight="50">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Grid Padding="0,0,8,0" Margin="4,0,4,0" xct:TouchEffect.LongPressCommand="{Binding Path=BindingContext.LongPressItemCommand, Source={x:Reference Name=lstView}}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<Label Text="{Binding ItemName}" TextColor="Black" Grid.Column="0" FontSize="Medium"></Label>
<Label Text="{Binding ItemDescription}" Grid.Column="1" VerticalTextAlignment="End"/>
</Grid>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
后面的代碼:
MessagingCenter.Subscribe<ItemViewModel, Guid>(this, "PopupMenuItemMsg",
(page, itemId) =>
{
Main_PopupMenu(itemId);
});
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