图像 - 长按

Question

有没有办法检测Xamarin Forms中图像控件的长按？

我使用轮播视图来显示图像，并希望通过长按选择来删除它们。

Answer 1

根据您在评论中的建议，这就是我所做的： （控件的目的是能够选择带有LongTap的图像）

我在PCL中定义了自己的Image控件：

• IsSelected BindableProperty。

• LongTap事件。

   public class MyImage:Image
  {
          private BindableProperty IsSelectedProperty = BindableProperty.Create("IsSelected", typeof(bool), typeof(MyImage), false);
  
      public bool IsSelected {
          get {
              return (bool)GetValue(IsSelectedProperty);
          }
          set {
              SetValue(IsSelectedProperty, value);
          }
      }
  
  
      public event EventHandler LongClick;
  
      public void OnLongClick()
      {
          IsSelected = !IsSelected;
  
          if(IsSelected)
          {
              Opacity = 0.5;
          }
          else
          {
              Opacity = 1;
          }
  
          if (LongClick != null)
          {
              LongClick(this, EventArgs.Empty);
          }
      }
  }
  

这是我的自定义渲染器:(在Android项目中定义）

[assembly: ExportRenderer(typeof(MyImage), typeof(MyImageRenderer))]
namespace PRISMCarouselView.Droid.Renderes
{
    public class MyImageRenderer : ImageRenderer
    {
        protected override void OnElementChanged(ElementChangedEventArgs<Image> e)
        {
            base.OnElementChanged(e);

            if (Control != null)
            {
                ImageView androidSource = Control as ImageView;
                MyImage myImage = e.NewElement as MyImage;

                androidSource.LongClick += (object sender, LongClickEventArgs ee) =>
                {
                    myImage.OnLongClick();
                };
            }
        }
    }
}

修改1：

这是一个稍微更新的版本，我使用BindingPropertyChangedDelegate来更改图像的不透明度：

 public class SelectableImage : Image
    {
        public SelectableImage()
        {

        }

        private static BindableProperty IsSelectedProperty = BindableProperty.Create("IsSelected",
        typeof(bool),
        typeof(SelectableImage),
        false, BindingMode.Default, null, (sender, o1, o2) => {

            SelectableImage imageControl = sender as SelectableImage;
            if(imageControl != null)
            {
                if(imageControl.IsSelected)
                {
                    imageControl.Opacity = 0.5;
                }else
                {
                    imageControl.Opacity = 1;
                }
            }
        });

        public bool IsSelected {
            get {
                return (bool)GetValue(IsSelectedProperty);
            }
            set {
                SetValue(IsSelectedProperty, value);
            }
        }


    }

渲染器：

[assembly: ExportRenderer(typeof(SelectableImage), typeof(SelectableImageRenderer))]
namespace Muserma.Apps.Droid.Renderer
{
    public class SelectableImageRenderer : ImageRenderer
    {
        protected override void OnElementChanged(ElementChangedEventArgs<Image> e)
        {
            base.OnElementChanged(e);

            if (Control != null)
            {
                ImageView androidSource = Control as ImageView;
                SelectableImage selectableImage = e.NewElement as SelectableImage;

                androidSource.LongClick += (object sender, LongClickEventArgs ee) =>
                {
                    selectableImage.IsSelected = !selectableImage.IsSelected;
                };
            }
        }

    }
}