如何在 WPF 中设置 ProgressBar 的可见性? [英] How to set the visibility of a ProgessBar in WPF?

问题描述

我最近才开始使用 WPF 并且正在尝试实现一个 ProgressBar，但无法让它做我想做的事情.

I just recently began working with WPF and am trying to implement a ProgressBar but can't get it to do what I want.

我想要的只是让 UI 在任务发生时显示进度条，否则它不应该是可见的.

All I want is for the UI to show the progress bar while a task is occurring, but it should not be visible otherwise.

这是我在 xaml 中的内容:

This what I have in the xaml:

<ProgressBar x:Name="pbarTesting" HorizontalAlignment="Left" Height="37"
    Margin="384,301,0,0" VerticalAlignment="Top" Width="264" IsHitTestVisible="True"
    IsIndeterminate="True" Visibility="Collapsed"/>

在我写的应用程序中:

progressBar.Visibility = Visibility.Visible;
doTimeConsumingStuff();
progressBar.Visibility = Visibility.Hidden;

但是，当我处理耗时的事情时，进度条永远不会出现.谁能告诉我我做错了什么?

However, when I get to the time consuming stuff, the progress bar never shows up. Can anyone tell me what I'm doing wrong?

推荐答案

WPF 开始时只有一个线程，称为 UI 线程.除了 UI 线程之外，UI 不会更新.当我们在 UI 线程中进行长时间运行的操作时；UI 更新停止.因此，当我们需要在长时间运行的操作中更新 UI 时，我们可以在 UI 线程以外的其他线程中启动长时间运行的操作.

WPF starts with only one thread which is called UI thread. UI doesn't update other than UI thread. When we do a long running operation in UI thread; Update of UI halts. So, when we need to update UI during a long running operation, we can start the long running operation in other thread than UI thread.

在以下示例中，我在后台线程中启动了一个长时间运行的操作.操作完成后，它返回一个值，我将其放入 UI 线程中.

In the following example I started a long running operation in a backgroud thread. When operation finish it returns a value and I took it in UI thread.

private void MethodThatWillCallComObject()
        {
            System.Threading.Tasks.Task.Factory.StartNew(() =>
            {
                //this will call in background thread
                return this.MethodThatTakesTimeToReturn();
            }).ContinueWith(t =>
            {
                //t.Result is the return value and MessageBox will show in ui thread
                MessageBox.Show(t.Result);
            }, System.Threading.Tasks.TaskScheduler.FromCurrentSynchronizationContext());
        }

        private string MethodThatTakesTimeToReturn()
        {
            System.Threading.Thread.Sleep(5000);
            return "end of 5 seconds";
        }

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