将图像 URL 从 Xamarin Forms PCL 加载到 Android 项目中的 PageRenderer 失败

Question

我正在传递来自网站的图像的 URL 字符串，这些图像出现在 PCL 项目的列表视图中，图像的 URL 传递给Android 自定义渲染器，但使用 MonoDroidToolKit 加载图像失败并出现以下错误：

未处理的异常：

System.ArgumentNullException: 值不能为空。参数名称：key

来自PCL（传递附件信息）：

    public partial class ImageViewPage : ContentPage
   {
    public ImageViewPage(Attachment imageItem)
    {
        if (imageItem == null)
            throw new ArgumentNullException();

        BindingContext = imageItem;
        _imageItem = imageItem.url;

        InitializeComponent();
    }

    public string _imageItem { get; private set; }
}

在 Android 自定义渲染器中：

 [assembly: ExportRenderer(typeof(ImageViewPage),typeof(ImageViewRenderer))]
 namespace BibleCodesApp.Droid
 {
 public class ImageViewRenderer : PageRenderer
 {
    global::Android.Views.View view;
    ImageLoader imageLoader;
    Activity activity;
    ImageView imageView;

    private string imageItem
    {
        get
        {
            var imageViewPage = Element as ImageViewPage;
            return imageViewPage == null
                ? null
                : imageViewPage._imageItem;
        }
    }

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

        activity = this.Context as Activity;
       view =  activity.LayoutInflater.Inflate
       (Resource.Layout.ImageView,this,false);

        imageLoader = new ImageLoader(activity, 512);
        imageView = FindViewById<ImageView>(Resource.Id.image_view);
        imageLoader.DisplayImage(imageItem, imageView, -1);
     }

   }
}

Android中的布局：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:local="http://schemas.android.com/apk/res-auto"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical">
<LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:padding="5dp">
    <BibleCodesApp.Droid.ScaleImageView
        android:id="@+id/image_view"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:scaleType="center"
        android:adjustViewBounds="true" />
</LinearLayout>
</RelativeLayout>

Answer 1

我现在看到了：您正在夸大您的新视图，但从未真正将其添加到页面！

你应该打电话给

        this.ViewGroup.AddView(view);

在 imageLoader.DisplayImage 通话结束后 OnElementChanged

Answer 2

这是正确的解决方案：

[assembly: ExportRenderer(typeof(ZoomImage), typeof(ZoomImageRenderer))]

命名空间WPAppTemplate.Droid { public class 缩放图像渲染器：图像渲染器 { 私人 ZoomImage _zoomImage；私有 ScaleImageView _scaleImage;

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

        if (e.NewElement != null)
        {
            _zoomImage = (ZoomImage)e.NewElement;

            // create the scale image and set it as the native control so it's available
            _scaleImage = new ScaleImageView(Context, null);
            _scaleImage.ZoomImage = _zoomImage;
            SetNativeControl(_scaleImage);
            await LoadImage();
        }
    }

    protected async override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);

        if (e.PropertyName == ZoomImage.AspectProperty.PropertyName
            || e.PropertyName == ZoomImage.HeightProperty.PropertyName
            || e.PropertyName == ZoomImage.WidthProperty.PropertyName)
        {
            _scaleImage.ZoomToAspect();
        }
        else if (e.PropertyName == ZoomImage.SourceProperty.PropertyName)
        {
            await LoadImage();
            _scaleImage.ZoomToAspect();
        }
        else if (e.PropertyName == ZoomImage.CurrentZoomProperty.PropertyName)
        {
            _scaleImage.ZoomFromCurrentZoom();
        }
        else if (e.PropertyName == ZoomImage.MaxZoomProperty.PropertyName)
        {
            _scaleImage.UpdateMaxScaleFromZoomImage();
        }
        else if (e.PropertyName == ZoomImage.MinZoomProperty.PropertyName)
        {
            _scaleImage.UpdateMinScaleFromZoomImage();
        }
    }

    private async Task LoadImage()
    {
        var image = await (new ImageLoaderSourceHandler()).LoadImageAsync(_zoomImage.Source, Context);
        try
        {
            if (image != null && image.ByteCount > 0)
                _scaleImage.SetImageBitmap(image);
        }
        catch (Exception e)
        {
            // catch an image loading failure
            Console.WriteLine($"Unable to load bitmap. Exception: {e.Message}");
        }
    }
}

将图像 URL 从 Xamarin Forms PCL 加载到 Android 项目中的 PageRenderer 失败

Loading an image URL from Xamarin Forms PCL to PageRenderer in Android project fails

custom-renderer

xamarin.android

xamarin