android - 在 ListView 中点击 Gesture 手势识别器不工作

Question

我的 ViewModel 中有这个:

public class MyClass: INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    int taps = 0;
    ICommand tapCommand;

    public MyClass()
    {
        tapCommand = new Command(OnTapped);
    }

    public ICommand TapCommand
    {
        get { return tapCommand; }
    }

    void OnTapped(object s)
    {
        taps++;
        Debug.WriteLine("parameter: " + s);
    }
}

这在 xaml 中:

<Image Source="delete.jpg" HeightRequest="20" WidthRequest="20">
     <Image.GestureRecognizers>
        <TapGestureRecognizer
            Command="{Binding TapCommand}"
            CommandParameter="Image1" />
    </Image.GestureRecognizers>
 </Image>

但是当单击图像时，输出日志中没有任何内容。我缺少什么？

Note 1: I've followed the guide here

Note 2: I'm debugging on Android Device

Update 1: full xaml here

Answer 1

你没有提供任何背后的代码，所以我不得不创建我自己的(见下文)。如果注释掉 ListView IsEnabled="False"

，您还可以为我节省 15 分钟

当您设置 Command="{Binding TapCommand} 时，TapCommand 对应于列表项的 TapCommand，而不是模型本身。因此，您有 2 个选项

1. 您可以在 MyItem 中实现点击(我不认为您想要那样，所以它的部分代码在下面的 MyItem 类中进行了注释)
2. 定义图像本身的上下文绑定(bind)。因为我们的 View 模型可以被创建几次——我们不希望这样，所以最好的解决方案是定义 View 模型的静态资源并在页面的任何地方使用它。解决方案如下(您只需要修改一些命名空间并将 delte.png 更改为您的 delete.jpg):

页面xml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:ButtonRendererDemo;assembly=ButtonRendererDemo"
             x:Class="ButtonRendererDemo.ImageTapComplexPage"
             BindingContext="{StaticResource viewModel}">

      <ContentPage.Resources>
        <ResourceDictionary>
          <local:TapComplexViewModel x:Key="viewModel"/>
        </ResourceDictionary>
      </ContentPage.Resources>


 <StackLayout>
    <Label Text="text2" VerticalOptions="Center" HorizontalOptions="Center" />
    <StackLayout Padding="0,20,0,20">
    <Button Text="text" Clicked="onclick" BackgroundColor="#009688"></Button>

    </StackLayout>
    <Label Text="List Type" VerticalOptions="Center" HorizontalOptions="Center" />
    <ListView x:Name="lstItems" RowHeight="60" ItemsSource="{Binding Items}" > <!--IsEnabled="False"-->
      <ListView.ItemTemplate>
        <DataTemplate>
          <ViewCell>
            <StackLayout Orientation="Horizontal" HorizontalOptions="Fill" Padding="0,2,0,2">
              <StackLayout Padding="5,5,5,5">
                <Image Source="{Binding source}" HorizontalOptions="End" HeightRequest="40" WidthRequest="40" />
              </StackLayout>
              <StackLayout Orientation="Vertical" Spacing="1">
                <Label Text = "{Binding name}" HeightRequest="20" FontAttributes="Bold"/>
                <Label Text = "{Binding data, StringFormat='{0:F0}'}" />
              </StackLayout>
              <StackLayout HorizontalOptions="EndAndExpand" Padding="0,0,15,0" Orientation="Horizontal">
                <Image Source="delete.png" HeightRequest="20" WidthRequest="20">
                   <Image.GestureRecognizers>
                    <!--<TapGestureRecognizer 
                        Command="{Binding TapCommand}"
                        CommandParameter="Image1" />-->
                        <TapGestureRecognizer Command="{Binding Source={StaticResource viewModel}, Path=TapCommand}" CommandParameter="{Binding name}" />
                 </Image.GestureRecognizers>
                </Image>
              </StackLayout>
            </StackLayout>
          </ViewCell>
        </DataTemplate>
      </ListView.ItemTemplate>
    </ListView>
  </StackLayout>
</ContentPage>

代码隐藏

namespace ButtonRendererDemo
{
    public partial class ImageTapComplexPage : ContentPage
    {
        public ImageTapComplexPage()
        {
            InitializeComponent();        
        }

        void onclick(object sender, EventArgs args)
        {

        }
    }

    public class TapComplexViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        int taps = 0;
        ICommand tapCommand;

        public ObservableCollection<MyItem> Items { get; private set; }
        public TapComplexViewModel()
        {
            Items = new ObservableCollection<MyItem>()
            {
                new MyItem { name="First", source="Icon.png", data=0.5f },
                new MyItem { name="Second", source="Icon.png", data=0.6f },
                new MyItem { name="Third", source="Icon.png", data=0.7f }
            };

            tapCommand = new Command(OnTapped);
        }

        public ICommand TapCommand
        {
            get { return tapCommand; }
        }

        void OnTapped(object s)
        {
            taps++;
            Debug.WriteLine("parameter: " + s);
        }



    }

    public class MyItem
    {
        public string name { get; set; }
        public string source { get; set; }
        public float data { get; set; }

        //public ICommand TapCommand
        //{
        //    get { return new Command(() => { }); }
        //}
    }
}