Question

我一直试图弄清楚下次更改BindableProperty时如何调用自定义渲染器OnElementChanged。

在我的情况下，为了理解目的，我需要刷新android，uwp，ios渲染器中的webview网址。

首次初始化值有效，但稍后当URL更改时，它不会调用。

如果在自定义渲染器类中有一个函数，那么我们可以调用并更新本机控件。

尝试使用android和uwp，但有同样的问题。一旦url加载进一步更改，它就不会刷新webview。

所以为了示例，我提供了UWP渲染器，如果它在这里工作，那么类似的更改可以在android渲染器中完成。但不确定在哪里做出改变才能使其发挥作用。

XAML

<StackLayout>
     <Entry Keyboard="Url" x:Name="txtUrl" Placeholder="Enter the URL" />

      <Button x:Name="ButtonImage" Text="Search"  Clicked="OnButtonClicked" />

     <local:HybridWebView x:Name="webView" />
</StackLayout>

Xaml.cs

    public partial class WebVieDemo : ContentPage
    {
        public WebVieDemo()
        {
            InitializeComponent();
            webView.Uri = "https://www.101cookbooks.com/archives/blueberry-beet-pancakes-vegan-recipe.html";
        }

        private void OnButtonClicked(object sender, EventArgs e)
        {
            txtUrl.Text = "https://stackoverflow.com/questions/1531093/how-do-i-get-the-current-date-in-javascript";
            webView.Uri = txtUrl.Text; // doesn't refresh the webview
        }
    }

HybridWebView.cs

    public class HybridWebView : WebView
    {
        public static readonly BindableProperty UriProperty = BindableProperty.Create(
          propertyName: "Uri",
          returnType: typeof(string),
          declaringType: typeof(HybridWebView),
          defaultValue: default(string));

        public string Uri
        {
            get { return (string)GetValue(UriProperty); }
            set { SetValue(UriProperty, value); }
        }

        public static readonly BindableProperty HtmlSourceProperty = BindableProperty.Create(
          propertyName: "HtmlSource",
          returnType: typeof(string),
          declaringType: typeof(HybridWebView),
          defaultValue: default(string));

        public string HtmlSource
        {
            get { return (string)GetValue(HtmlSourceProperty); }
            set { SetValue(HtmlSourceProperty, value); }
        }
    }

UWP渲染器

[assembly: ExportRenderer(typeof(HybridWebView), typeof(WindowsWebViewRenderer))]
namespace DemoApp.UWP
{
    public class WindowsWebViewRenderer : ViewRenderer<HybridWebView, WebView>
    {
        HybridWebView hybridWebView = null;
        protected override void OnElementChanged(ElementChangedEventArgs<HybridWebView> e)
        {
            base.OnElementChanged(e);
            if (Control == null)
            {
                // Create the native control and use SetNativeControl
                var webView = new WebView();
                webView.LoadCompleted += WebView_LoadCompleted;
                SetNativeControl(webView);
            }
            if (e.OldElement != null)
            {
                // Cleanup resources and remove event handlers for this element.
            }
            if (e.NewElement != null)
            {
                // Use the properties of this element to assign to the native control, which is assigned to the base.Control property
                hybridWebView = e.NewElement;
                if (hybridWebView.Uri != null)
                    Control.Source = new Uri(e.NewElement.Uri);
            }
        }

        async private void WebView_LoadCompleted(object sender, Windows.UI.Xaml.Navigation.NavigationEventArgs e)
        {
            hybridWebView.HtmlSource = await Control.InvokeScriptAsync("eval", new string[] { "document.documentElement.outerHTML;" });
        }
    }
}

Answer 1

在自定义渲染器中，您需要为此重写OnElementPropertyChanged，而不是OnElementChanged，如下所示：

    protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);
        if (e.PropertyName == HybridWebView.UriProperty.PropertyName)
        {
            if (Control.Uri != null)
                Control.Source = new Uri(Control.Uri);
        }
    }

在Xamarin Forms

1 个答案: