Question

有没有办法让控件允许我使用 ONLY Xamarin.Forms控件进行缩放和缩放。

我希望在xamarin.forms（WebView或Image或任何其他）的任何控件中显示图像，并能够从应用程序进行缩放。

Answer 1

截至本文发布之时，无法使用纯内置Forms控件进行捏合/缩放。有一种方法可以实现这一点，但您必须为此实现本机渲染器。

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，该类具有诸如最小/最大触摸点数和要侦听的事件之类的属性。

在iOS项目中，我为我的视图制作了一个自定义渲染器，渲染器从视图中获取属性并连接触摸事件侦听器。

此外，我创建了一个可附加属性（也称为Behavior），可以应用于其他视图，并在应用时从其父视图中获取视图，将其包装在PanGestureRecognizer中，另一个附加属性以相同的方式充当事件侦听器包装器。

这是一个完整的黑客，但在Xamarin干净地实现之前，它涵盖了缺少的功能

更新：现在使用示例代码严重删除，因为发布的内容太多了，它应该让您知道如何实现这一点，而不是复制/粘贴解决方案。如果它看起来似乎太多了，我肯定有更好的方法，但它会成功，直到这个功能被烘焙。

  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());
    }
}

Answer 2

我最终使用元视口进行缩放，如下所示。这可能不是每个人的解决方案，但它对我有用。

将图像hex -64放在下面的image标签内，然后将整个html放在WebView中。

this.WebView.Source = new HtmlWebViewSource { BaseUrl = URL, Html = html };

The html will be defined here.
<!DOCTYPE html>
<html lang="en-us">
<head>
    <meta name="viewport" content="width=device-width, initial-scale=0.25, maximum-scale=3.0 user-scalable=1">
    <title></title>
    <style>
        body {
            margin: 0 20px 0 0;
            font-family: HelveticaNeue-Light, HelveticaNeue-UltraLight, Helvetica, Consolas, 'Courier New';
        }

        table {
            width: 100%;
            border: 1px outset;
            border-color: #3c4142;
        }

        td {
            font-size: 8px;
        }
    </style>
</head>
<body>
    <img src="data:image/png;base64,YourBase64imagestringhere" style="width:100%" />
</body>
</html>

Answer 3

使用Nuget的Mr.Gestures包：https://www.nuget.org/packages/MR.Gestures/

Xamarin.forms捏和缩放

3 个答案: