为什么全局对象会导致无法工作的代码？

Question

我有一个非常基本的 android 应用程序。其中大部分仍然来自模板。我为 XMPP 客户端使用自己的类库。现在发生的事情是，如果我声明一个全局 TextView 用于事件或不同的方法（OnCreate、OnResume 等），我的事件似乎不会被引发。 我的图书馆绝对不是原因，因为我在不同的情况下对其进行了测试。

[Activity(Label = "@string/app_name", Theme = "@style/AppTheme.NoActionBar", MainLauncher = true)]
    public class MainActivity : AppCompatActivity
    {
        public XMPPClient client;
        TextView consoleText;

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.activity_main);

            Android.Support.V7.Widget.Toolbar toolbar = FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
            SetSupportActionBar(toolbar);

            FloatingActionButton fab = FindViewById<FloatingActionButton>(Resource.Id.fab);
            fab.Click += FabOnClick;

            //consoleText = FindViewById<TextView>(Resource.Id.consoleText);

            client = new XMPPClient("10.0.2.2", 5222, "chris3", "Define")
            {
                AuthenticationInfo = true
            };

            client.OnPublishEvent += Client_OnPublishEvent;
            client.OnConnection += Client_OnConnection;
            client.OnMessageReceived += Client_OnMessageReceived;
        }

        private void Client_OnMessageReceived(object sender, MessageEventArgs e)
        {
            //consoleText.Text += "\nMessage: " + e.text + " from " + e.from;
            Log.Debug("mytag", "Message!");
        }

        private void Client_OnPublishEvent(object sender, SubscriptionEventArgs e)
        {
            //consoleText.Text += "\nPublication: " + e.title + " with content " + e.content + " at " + e.published;
            Log.Debug("mytag", "Publication");
        }

        private void Client_OnConnection(object sender, ConnectionEventArgs e)
        {
            //consoleText.Text += "\nConnection status changed: " + e.Status;
            Log.Debug("mytag", "ConnectionChange");
        }

        public override bool OnCreateOptionsMenu(IMenu menu)
        {
            MenuInflater.Inflate(Resource.Menu.menu_main, menu);
            return true;
        }

        public override bool OnOptionsItemSelected(IMenuItem item)
        {
            int id = item.ItemId;
            if (id == Resource.Id.action_subscribe)
            {
                client.Subscribe("Node1");
                Log.Debug("mytag", "Subscribed");
                return true;
            }

            return base.OnOptionsItemSelected(item);
        }

        private void FabOnClick(object sender, EventArgs eventArgs)
        {
            View view = (View) sender;
            client.Connect();
        }
    }

当 TextView 控制台文本对象存在时，我的 OnConnection 事件在开始时被触发，当我关闭客户端时。 但是，如果它不存在，则每个事件都可以正常工作。 现在我是 Xamarin 的初学者，我对问题的根源非常感兴趣。

Answer 1

您可能需要封装要针对主调度程序（UI 线程）处理的文本分配。

例如，它看起来像这样。

private void Client_OnMessageReceived(object sender, MessageEventArgs e)
{
    Activity.RunOnUiThread(() => {
        consoleText.Text += "\nMessage: " + e.text + " from " + e.from;
    });

    Log.Debug("mytag", "Message!");
}

试一试，如果它仍然有错误，请告诉我，不要忘记你需要将所有 consoleText.Text 分配包含在其中。

Activity.RunOnUiThread(() => {
});

// You might not need the Activity part, I can't remember exactly which 
// one it is for an AppCompatActivity.

RunOnUiThread(() => {
});