带有未更新 ui 的任务的按钮单击事件

Question

我有一个按钮单击事件，它在其中执行一项很长的任务（可能从 3 秒到 3 分钟不等）

        private void B_Clicked(object sender, EventArgs e)
        {
            bumpPop.Dismiss();
            SfPopupLayout loadPop = new SfPopupLayout();
            DataTemplate loadView = new DataTemplate(() =>
            {
                SfBusyIndicator busy = new SfBusyIndicator();
                return busy;
            });
            loadPop.PopupView.ContentTemplate = loadView;
            loadPop.Show();
            if (String.IsNullOrEmpty((string)gradeSel.SelectedValue) || String.IsNullOrWhiteSpace((string)gradeSel.SelectedValue))
            {
                gradeSel.Watermark = "Please select a grade";
                loadPop.Dismiss();
                bumpPop.Show();
            }
            else
            {
                string grade = (string) gradeSel.SelectedValue;

                Task.Run(() => BumpGrade(grade)).Wait();
                UpdateOverallScore();
                AssList.ItemsSource = Asses;
                loadPop.Dismiss();


            }
        }

每当触发事件时，用户界面都不会更新，直到任务完成。即使我在事件触发后立即调用的 UI 更新也不会在任务完成之前发生。我该怎么办？

更新：这对我有用

        private async void B_Clicked(object sender, EventArgs e)
        {
            await PreBumpWork();
            Device.BeginInvokeOnMainThread(() => {
                loadPop.Dismiss();
                loadPop.IsOpen = false;
                loadPop.IsVisible = false;
            });
        }

        private Task PreBumpWork()
        {
            return Task.Factory.StartNew(() =>
            {
                Device.BeginInvokeOnMainThread(() =>
                {
                    bumpPop.Dismiss();
                    DataTemplate loadView = new DataTemplate(() =>
                    {
                        SfBusyIndicator busy = new SfBusyIndicator();
                        busy.IsBusy = true;
                        return busy;
                    });
                    loadPop.PopupView.ContentTemplate = loadView;
                    loadPop.PopupView.ShowFooter = false;
                    loadPop.PopupView.ShowHeader = false;
                    loadPop.ClosePopupOnBackButtonPressed = false;
                    loadPop.Show();
                });

                if (String.IsNullOrEmpty((string)gradeSel.SelectedValue) || String.IsNullOrWhiteSpace((string)gradeSel.SelectedValue))
                {
                    Device.BeginInvokeOnMainThread(() => {
                        gradeSel.Watermark = "Please select a grade";
                        loadPop.Dismiss();
                        bumpPop.Show();
                    });
                }
                else
                {
                    string grade = (string)gradeSel.SelectedValue;

                    Task.Run(async () => await BumpGrade(grade));
                }
            });
        }

Answer 1

您可以尝试在不同的线程中运行您的代码，并在线程方法中使用委托（操作）更新 UI - 添加\删除对（来自）线程方法的其他调用。 例如：

private void B_Clicked(object sender, EventArgs e)
    {
        bumpPop.Dismiss();
        SfPopupLayout loadPop = new SfPopupLayout();
        DataTemplate loadView = new DataTemplate(() =>
        {
            SfBusyIndicator busy = new SfBusyIndicator();
            return busy;
        });
        loadPop.PopupView.ContentTemplate = loadView;
        loadPop.Show();
        if (String.IsNullOrEmpty((string)gradeSel.SelectedValue) || String.IsNullOrWhiteSpace((string)gradeSel.SelectedValue))
        {
            gradeSel.Watermark = "Please select a grade";
            loadPop.Dismiss();
            bumpPop.Show();
        }
        else
        {
            string grade = (string)gradeSel.SelectedValue;
            object val = new string[] { grade, loadPop };
            Thread thread = new Thread(MyMethod);
            thread.Start(val);
        }
    }

    private void MyMethod(object Data)
    {
        Invoke(new Action(() => UpdateApplicationUI(Data)));
    }

    private void UpdateApplicationUI(object Data)
    {
        object[] items = (object[])Data;
        string grade = items[0] as string;
        SfPopupLayout loadPop = items[1] as SfPopupLayout;
        BumpGrade(grade);
        UpdateOverallScore();
        AssList.ItemsSource = Asses;
        loadPop.Dismiss();
    }

Answer 2

Device.BeginInvokeOnMainThread (() => {
 //put your UI updates here
});

这将强制您的代码在主线程上执行它。 同样删除.Wait();，就像彼得说的那样，会导致死锁。