从另一个类调用MainActivity方法时出错

Question

我在我的MainActivity.cs有以下api电话 -

    public async Task DoSomething()
    {
        var progressDialog = ShowLoading(_instance);

        await Task.Factory.StartNew(() =>
        {
            var objectResponse = string.Empty;
            string _apiUrl = "https://my-web-service-endpoint";

            var request = (HttpWebRequest)WebRequest.Create(_apiUrl);
            request.Method = "GET";

            using (var response = _request.HttpWebResponse(request))
            {
                objectResponse = _request.HttpWebResponseBody(response);
            }

            progressDialog.Dismiss();
        });
    }

我通过SliderControl.cs中的按钮单击调用此方法 -

    public void loadTestView(View view)
    {
        Button btnDoSomething = view.FindViewById<Button>(Resource.Id.btnDoSomething);
        if (btnDoSomething != null)
        {
            btnDoSomething .Click += async (sender, e) =>
            {
                 await MainActivity.GetInstance().DoSomething();
            };
        }
    }

然而loadTestView不是在MainActivity.cs中调用而是在使用滑动到应用程序中的特定视图并在SliderControl.cs中处理时调用它，它被设置为 -

public override Java.Lang.Object InstantiateItem(ViewGroup container, int position)
            {
                var selectedView = Resource.Layout.Locator;

                if (position == 0)
                {
                    selectedView = Resource.Layout.Main;
                }
                if (position == 1)
                {
                    selectedView = Resource.Layout.TestView;
                }

                View view = LayoutInflater.From(container.Context).Inflate(selectedView, container, false);
                container.AddView(view);

                if (position == 0)
                {
                    loadMainView(view);
                }
                else if (position == 1)
                {
                    loadTestView(view);
                }

                return view;
            }

当我设置不同的按钮时，单击MainActivity.cs中的事件逻辑，一切都相应地工作，但是当设置按钮点击登录时，我遇到了错误 -

Only the original thread that created a view hierarchy can touch its views. 

奇怪的是装载机实际上已经进入视野，但是当我进入await Task.Factory.StartNew(() =>线时，错误命中。

我已经尝试更改线路以使用Task.Run而不是相同的错误，并且还在Device.BeginInvokeOnMainThread上找到了一些信息，而不管相信这是用于Xamarin Forms。我怎样才能让它发挥作用？

Answer 1

您应该使用UI线程来更新UI /或涉及UI的任何任务：

样本表单示例：

Device.BeginInvokeOnMainThread (() => {
  label.Text = "Async operation completed";
});

John写了一些很好的例子来描述如何使用Async / Await模式。你可能想在这里阅读更多https://johnthiriet.com/configure-await/#

更新：对于Xamarin Native -

问题：

new System.Threading.Thread(new System.Threading.ThreadStart(() => {
    lblTest.Text = "updated in thread"; 
    // Doesn't work because you can't modify UILabel on background thread!
})).Start();

解：

new System.Threading.Thread(new System.Threading.ThreadStart(() => {
    InvokeOnMainThread (() => {
        label1.Text = "updated in thread"; 
        // this works! We are invoking in Main thread.
    });
})).Start();