Xamarin Android FFImageLoading ImageService.Instance.LoadUrl() System.NullReferenceException

问题描述

FFImageLoading 有一个奇怪的问题.编译器不显示任何错误，但是当应用程序在设备上启动时，抛出异常:System.NullReferenceException.

I've got a strange problem with FFImageLoading. Compiler don't show any error, but while application is starting on device, there is thrown an exception:System.NullReferenceException.

代码:

C#

private void setUserImage()
{
    ImageService.Instance.Initialize();
    imgThunbailUsername = FindViewById<ImageViewAsync>(Resource.Id.imgDisplay);
    string url = @"https://lh4.googleusercontent.com/-Lfgi-xEMwuk/VNWoy8EDWcI/AAAAAAAAACk/rwsluNfhSZY/w1486-h832-no/photo.jpg";

    ImageService.Instance.LoadUrl(url)
        .Retry(3, 200)
        .DownSample(60, 60)
        .Into(imgThunbailUsername); // compiler points here with an exception
}

XML

<FFImageLoading.Views.ImageViewAsync
  android:id="@+id/imgDisplay"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:scaleType="fitCenter" />

如果您提供 Xamarin 中的任何提示、想法或什至另一个用于图像的好工具，我将不胜感激.

---

I'd be thankful for any tip, idea, or even another good tool for images in Xamarin.

推荐答案

好的，我知道出了什么问题.下面的 XML 不直接在 ViewModel 下.

Okay, I found out what's wrong. XML below is not directly under ViewModel.

<FFImageLoading.Views.ImageViewAsync
  android:id="@+id/imgDisplay"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:scaleType="fitCenter" />

里面调用了那边的XML

XML over there is called inside

<android.support.design.widget.NavigationView
  android:layout_width="wrap_content"
  android:layout_height="match_parent"
  android:layout_gravity="start"
  android:background="@android:color/white"
  android:id="@+id/nav_view"
  app:headerLayout="@layout/drawer_header" <!-- here -->
  app:menu="@menu/navmenu" />
</android.support.v4.widget.DrawerLayout>

所以在这种情况下，我必须正确调用视图:

So in this case I have to call properly view:

View headerLayout = navigationView.InflateHeaderView(Resource.Layout.drawer_header);

等使用 FindViewById 之类的:

imgThunbailUsername = headerLayout.FindViewById<ImageViewAsync>(Resource.Id.imgDisplay);

所以我需要做的就是使用 InflateHeaderView 获取一个 View headerlayout.

So all I need to do is just get a View headerlayout with InflateHeaderView.

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