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尝试在Xamarin窗体上实现ImagePicker时出错

xamarin.android xamarin.forms xamarin c#

Theodorus Agum Gumilang · 技术社区 · 8 年前

您好,我试图在我的xamarin表单上实现ImagePicker,但我的MainActivty OnActivityResult有问题,每当我选择图像时,它都会收到此错误消息

android.runtime.JavaProxyThrowable: System.NullReferenceException: Object reference not set to an instance of an object
  at Microsoft.Identity.Client.WebUI.SetAuthorizationResult (Microsoft.Identity.Client.Internal.AuthorizationResult authorizationResultInput) [0x00006] in <df3bbcf06538443e9963d82dd707b6fa>:0 
  at Microsoft.Identity.Client.AuthenticationAgentContinuationHelper.SetAuthenticationAgentContinuationEventArgs (System.Int32 requestCode, Android.App.Result resultCode, Android.Content.Intent data) [0x00032] in <df3bbcf06538443e9963d82dd707b6fa>:0 
  at KGVC.Droid.MainActivity.OnActivityResult (System.Int32 requestCode, Android.App.Result resultCode, Android.Content.Intent data) [0x0000b] in <e83f90a066ab4f6c95402217456751e2>:0 
  at Android.Support.V4.App.FragmentActivity.n_OnActivityResult_IILandroid_content_Intent_ (System.IntPtr jnienv, System.IntPtr native__this, System.Int32 requestCode, System.Int32 native_resultCode, System.IntPtr native_data) [0x00014] in <7a2a36256f1648ecbd0c15a75bc5a349>:0 
  at (wrapper dynamic-method) System.Object:409b2b82-0807-4c59-b475-d61eb538da78 (intptr,intptr,int,int,intptr)
    at md5926298ec23f3b6e841a6fb18f139a084.MainActivity.n_onActivityResult(Native Method)
    at md5926298ec23f3b6e841a6fb18f139a084.MainActivity.onActivityResult(MainActivity.java:39)
    at android.app.Activity.dispatchActivityResult(Activity.java:6533)
    at android.app.ActivityThread.deliverResults(ActivityThread.java:3919)
    at android.app.ActivityThread.handleSendResult(ActivityThread.java:3966)
    at android.app.ActivityThread.access$1500(ActivityThread.java:180)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1545)
    at android.os.Handler.dispatchMessage(Handler.java:111)
    at android.os.Looper.loop(Looper.java:207)
    at android.app.ActivityThread.main(ActivityThread.java:5795)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:768)

我对这个问题的第一个想法是,我的PicturePickerImplementation中的resultcode替换了AzureB2c的resultcode,这是因为当我尝试删除此代码时 AuthenticationAgentContinuationHelper.SetAuthenticationAgentContinuationEventArgs(requestCode, resultCode, data); 从我的OnActivityResult来看,它将起到魅力的作用,我的问题是如何解决这一冲突? 这是我的完整代码

public static readonly int PickImageId=1000;

public TaskCompletionSource<Stream> PickImageTaskCompletionSource { set; get; }
protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
    {
        base.OnActivityResult(requestCode, resultCode, data);
        AuthenticationAgentContinuationHelper.SetAuthenticationAgentContinuationEventArgs(requestCode, resultCode, data);

        if (requestCode == PickImageId)
        {
            if ((resultCode == Result.Ok) && (data != null))
            {
                Android.Net.Uri uri = data.Data;
                Stream stream = ContentResolver.OpenInputStream(uri);

                // Set the Stream as the completion of the Task
                PickImageTaskCompletionSource.SetResult(stream);
            }
            else
            {
                PickImageTaskCompletionSource.SetResult(null);
            }
        }
    }

这是我的家属服务

using System;
using System.IO;
using System.Threading.Tasks;

using Android.Content;

using Xamarin.Forms;

using KGVC.Droid;
using KGVC.Interfaces;

[assembly: Dependency(typeof(PicturePickerImplementation))]
namespace KGVC.Droid
{
    public class PicturePickerImplementation : IPicturePicker
    {
        public Task<Stream> GetImageStreamAsync()
        {
            // Define the Intent for getting images
            Intent data = new Intent();
            data.SetType("image/*");
            data.SetAction(Intent.ActionGetContent);

            // Get the MainActivity instance
            MainActivity activity = Forms.Context as MainActivity;

            // Start the picture-picker activity (resumes in MainActivity.cs)
            activity.StartActivityForResult(
                Intent.CreateChooser(data, "Select Picture"),
                MainActivity.PickImageId);

            // Save the TaskCompletionSource object as a MainActivity property
            activity.PickImageTaskCompletionSource = new TaskCompletionSource<Stream>();

            // Return Task object
            return activity.PickImageTaskCompletionSource.Task;
        }
    }
}

有什么解决我问题的建议吗?谢谢 编辑: 经过一点观察,我注意到一些奇怪的行为触发了这个错误。我的错误只有在我成功登录后才会出现,然后我关闭应用程序并从后台将其杀死,要使我的选择器图像正常工作,我应该做的是1。使我的应用程序在后台2上运行。再次重新登录,我可以再次使用图像选择器。有人遇到过这个问题吗?

1 回复 | 直到 8 年前

Elvis Xia - MSFT 8 年前

我对这个问题的第一个想法是,我的PicturePickerImplementation中的resultcode替换了AzureB2c的resultcode,这是因为当我尝试删除这个代码AuthenticationAgentContinuationHelper时。SetAuthenticationAgentContinuationEventArgs(请求代码、结果代码、数据);从我的OnActivityResult来看,它将起到魅力的作用,我的问题是如何解决这一冲突?

OnActivityResult 将在您呼叫时触发 PublicClientApplication.AcquireTokenAsync 当你打电话的时候 StartActivityForResult . 因此,应根据请求代码将两部分逻辑分开:

if (requestCode == PickImageId)
    {
        if ((resultCode == Result.Ok) && (data != null))
        {
            Android.Net.Uri uri = data.Data;
            Stream stream = ContentResolver.OpenInputStream(uri);

            // Set the Stream as the completion of the Task
            PickImageTaskCompletionSource.SetResult(stream);
        }
        else
        {
            PickImageTaskCompletionSource.SetResult(null);
        }
    }else
    {
      AuthenticationAgentContinuationHelper.SetAuthenticationAgentContinuationEventArgs(requestCode, resultCode, data);
    }