ios - Xamarin.forms 捏合和缩放

Question

有没有一种方法可以让我使用 ONLY Xamarin.Forms 控件进行捏合和缩放。

我想在 xamarin.forms(WebView 或图像或任何其他)的任何控件中显示图像，并能够从应用程序缩放。

Answer 1

截至本文发布时，还没有一种方法可以使用纯内置的 Forms 控件进行缩放。有一种方法可以实现这一点，但您必须为此实现原生渲染器。

我通过创建一个继承自 Xamarin.Forms.ContentView - PanGestureContainer 的类在我正在编写的应用程序中实现了这一点，该类具有触摸点最小/最大数量和要监听的事件等属性。

在 iOS 项目中，我为我的 View 制作了一个自定义渲染器，其中渲染器从 View 中获取属性并连接触摸事件监听器。

此外，我制作了一个可应用于其他 View 的可附加属性(又名行为)，当应用它时，它从其父 View 中获取 View ，将其包装在 PanGestureRecognizer 中，另一个附加属性以相同的方式充当事件监听器包装器。

这是一个完整的 hack，但在 Xamarin 干净地实现它之前覆盖了缺失的功能

---

更新:现在有了示例代码，严重精简 因为发布太多，它应该让您了解如何实现这一点，而不是复制/粘贴解决方案。如果它看起来可能太多了，我相信有更好的方法，但它会起到作用，直到这个功能被内置。

  public abstract class BaseInteractiveGestureRecognizer : BindableObject, IInteractiveGestureRecognizer
    {
        public static readonly BindableProperty CommandProperty = BindableProperty.Create<BaseInteractiveGestureRecognizer, ICommand> ((b) => b.Command, null, BindingMode.OneWay, null, null, null, null);

        public ICommand Command {
            get {
                return (ICommand)base.GetValue (BaseInteractiveGestureRecognizer.CommandProperty);
            }
            set {
                base.SetValue (BaseInteractiveGestureRecognizer.CommandProperty, value);
            }
        }

        public object CommandParameter {get;set;} // make bindable as above

        public GestureState State { get;set;} // make bindable as above

        public View SourceView{ get; set; } 

        public void Send ()
        { 
            if (Command != null && Command.CanExecute (this)) {
                Command.Execute (this);
            }
        }
    }

public class PanGesture : BaseInteractiveGestureRecognizer
{
    public uint MinTouches { get;set; } // make bindable
    public uint MaxTouches { get;set; } // make bindable
    // add whatever other properties you need here - starting point, end point, touch count, current touch points etc.
}

然后在iOS项目中:

public abstract class BaseInteractiveGestureRenderer : BindableObject,IGestureCreator<UIView>
    {
        public abstract object Create (IInteractiveGestureRecognizer gesture, Element formsView, UIView nativeView);

        public static GestureState FromUIGestureState (UIGestureRecognizerState state)
        {
            switch (state) {
            case UIGestureRecognizerState.Possible:
                return GestureState.Possible;
            case UIGestureRecognizerState.Began:
                return GestureState.Began;
            case UIGestureRecognizerState.Changed:
                return GestureState.Update;
            case UIGestureRecognizerState.Ended:
                return GestureState.Ended;
            case UIGestureRecognizerState.Cancelled:
                return GestureState.Cancelled;
            case UIGestureRecognizerState.Failed:
                return GestureState.Failed; 
            default:
                return GestureState.Failed;
            }    
        }
    }


using StatementsHere;
[assembly: ExportGesture (typeof(PanGesture), typeof(PanGestureRenderer))]
namespace YourNamespaceHere.iOS
{
public class PanGestureRenderer : BaseInteractiveGestureRenderer
{
    public PanGestureRenderer () : base ()
    {   
    }

    #region IGestureCreator implementation

    public override object Create (IInteractiveGestureRecognizer gesture, Element formsView, UIView nativeView)
    {   
        PanGesture panGesture = gesture as PanGesture; 
        nativeView.UserInteractionEnabled = true; 

        UIPanGestureRecognizer panGestureRecognizer = null;
        panGestureRecognizer = new UIPanGestureRecognizer (() => panGesture.Send());
    }
}