Xamarin BindableProperty 不调用设置器

Question

我的自定义组件中的 Uri 属性有问题

我的自定义 WebView 组件：

public class PdfWebView : WebView
{ 
    public static readonly BindableProperty UriProperty = BindableProperty.Create(nameof(Uri), typeof(string), typeof(PdfWebView), default(string), propertyChanged: OnUriPropertyChanged);

    private static void OnUriPropertyChanged(BindableObject bindable, object oldValue, object newValue)
    {
        if(oldValue != newValue)
        {

        }
    }

    public string Uri
    {
        get { return (string)GetValue(UriProperty); }
        set { SetValue(UriProperty, value); } // need call but it`s doesnt work
    }
}

XAML：

<controls:PdfWebView
            x:Name="PdfView"
            Uri="{Binding Uri}"
            IsVisible="{Binding IsLoaderVisible, Converter={StaticResource BoolReverseConverter}}"
            Margin="0"
            HorizontalOptions="FillAndExpand"
            VerticalOptions="FillAndExpand"
            Navigated="WebView_Navigated"/>

渲染器：

[assembly: ExportRenderer(typeof(PdfWebView), typeof(PdfWebViewRenderer))]
namespace Contrinex.Droid.Renderers
{
    public class PdfWebViewRenderer : WebViewRenderer
    {
        public PdfWebViewRenderer(Context context) : base(context)
        {
        }

        protected override void OnElementChanged(ElementChangedEventArgs<WebView> e)
        {
            base.OnElementChanged(e);

            if (e.NewElement != null)
            {
                Control.Settings.JavaScriptEnabled = true;
                Control.Settings.AllowFileAccess = true;
                Control.Settings.AllowFileAccessFromFileURLs = true;
                Control.Settings.AllowUniversalAccessFromFileURLs = true;
            }
        }

        protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            base.OnElementPropertyChanged(sender, e);
            if (e.PropertyName == PdfWebView.UriProperty.PropertyName)
            {
                var docView = Element as PdfWebView;
                Control.LoadUrl($"file:///android_asset/pdfjs/web/viewer.html?file={($"file:///{docView.Uri.Trim('/')}")}");
            }
        }
    }
}

Uri 属性中的值已更改，但 setter 不调用

Answer 1

根据您的描述，您的意思是您更改了 Uri 属性，但 PdfWebview 中的 BindableProperty UriProperty 不会更改。

如果是，请在 Rebder 中添加OnElementPropertyChanged方法，如下所示：

 protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);
        PdfWebView pdfWebView = sender as PdfWebView;
        if (e.PropertyName == "Uri")
        {
            Control.LoadUrl(string.Format("file:///android_asset/pdfjs/web/viewer.html?file={0}", string.Format("file:///android_asset/Content/{0}", WebUtility.UrlEncode(pdfWebView.Uri))));
        }
    }

关于 webview 渲染的完整代码：

public  class PdfWebViewRenderer: WebViewRenderer
{
    public PdfWebViewRenderer(Context context) : base(context)
    {

    }

    protected override void OnElementChanged(ElementChangedEventArgs<WebView> e)
    {
        base.OnElementChanged(e);

        if (e.NewElement != null)

        {

            var pdfView = Element as PdfWebView;

            Control.Settings.AllowUniversalAccessFromFileURLs = true;

            Control.LoadUrl(string.Format("file:///android_asset/pdfjs/web/viewer.html?file={0}", string.Format("file:///android_asset/Content/{0}", WebUtility.UrlEncode(pdfView.Uri))));

        }
    }

    protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);
        PdfWebView pdfWebView = sender as PdfWebView;
        if (e.PropertyName == "Uri")
        {
            Control.LoadUrl(string.Format("file:///android_asset/pdfjs/web/viewer.html?file={0}", string.Format("file:///android_asset/Content/{0}", WebUtility.UrlEncode(pdfWebView.Uri))));
        }
    }
}

截图：