Question

我在非常简单的情况下使用 MvxImageViewLoader 。

在 ViewDidLoad ：

上

        var pnlBackImage = new UIImageView(new RectangleF(0, 0, pnlBack.Frame.Width, pnlBack.Frame.Height));
        Add(pnlBackImage);
        pnlBackImageLoader = new MvxImageViewLoader(() => pnlBackImage);

        ...

        set.Bind(pnlBackImageLoader).To(x => x.UserBackgroundUrl);

其中UserBackgroundUrl是公共字符串属性。

但是在 set.Apply（）上，我在日志和图片中看到以下内容未加载：

2013-06-24 13:51:26.999 SPBTouch[446:21b03] MvxBind: Error:   2.78 Problem seen during binding execution for from UserBackgroundUrl to ImageUrl - problem TargetInvocationException: Exception has been thrown by the target of an invocation.
      at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x000d9] in /Developer/MonoTouch/Source/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:236 
  at System.Reflection.MonoProperty.SetValue (System.Object obj, System.Object value, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] index, System.Globalization.CultureInfo culture) [0x00064] in /Developer/MonoTouch/Source/mono/mcs/class/corlib/System.Reflection/MonoProperty.cs:353 
  at System.Reflection.PropertyInfo.SetValue (System.Object obj, System.Object value, System.Object[] index) [0x00000] in /Developer/MonoTouch/Source/mono/mcs/class/corlib/System.Reflection/PropertyInfo.cs:93 
  at Cirrious.MvvmCross.Binding.Bindings.Target.MvxPropertyInfoTargetBinding.SetValue (System.Object value) [0x00000] in <filename unknown>:0 
  at Cirrious.MvvmCross.Binding.Bindings.MvxFullBinding.UpdateTargetFromSource (Boolean isAvailable, System.Object value) [0x00000] in <filename unknown>:0 
InnerException was NullReferenceException: Object reference not set to an instance of an object
      at Cirrious.MvvmCross.Binding.Views.MvxBaseImageViewLoader`1[MonoTouch.UIKit.UIImage].set_ImageUrl (System.String value) [0x00000] in <filename unknown>:0 
  at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
  at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x000c0] in /Developer/MonoTouch/Source/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:228

我甚至将图像加载器甚至图像面板定义为视图字段，但仍然没有运气。什么可能导致这个问题？

谢谢。

Answer 1

您列出的内部异常错误是：

NullReferenceException：未将对象引用设置为对象的实例在Cirrious.MvvmCross.Binding.Views.MvxBaseImageViewLoader`1 [MonoTouch.UIKit.UIImage] .set_ImageUrl（System.String value）[0x00000] in：0

我猜这会导致NullReferenceException中的set：

    public string ImageUrl
    {
        get { return _imageHelper.ImageUrl; }
        set { _imageHelper.ImageUrl = value; }
    }

如果_imageHelper为空

查看MvxBaseImageViewLoader.cs#L31如果显示此错误消息Unable to resolve the image helper - have you referenced and called EnsureLoaded on the DownloadCache plugin?

，就会发生这种情况

是否显示此错误消息？如果是这样，您的应用程序中是否加载了DownloadCache插件（以及它的依赖插件File）？

如果这没有帮助，请尝试比较您的应用，以便N + 1中的某些应用。几个N + 1个视频中涵盖了图像视图的成功使用 - http://mvvmcross.wordpress.com/ - 例如N = 2或N = 3

Answer 2

按照MvvmCross CollectionView example上的教程，当我遇到本问题中提到的相同错误（异常）时，我来到这里。如果您错过了注册/安装插件，我发现您收到此错误。我通过安装以下插件解决了错误：

安装包MvvmCross.ITSparta.Plugin.DownloadCache

安装包MvvmCross.ITSparta.Plugin.File

安装这些插件后，会在UI项目（iOS / Android）中创建新文件，并注册这些插件。因此，您不会收到此错误。

MvxImageViewLoader绑定无法正常工作

2 个答案: