Question

How to kill one button’s event when a new button is clicked.

I have one event (Button G) running.(has a while loop waiting for some input).
I have a another button for quit operation.
Now. I cannot click any other button when button G’s event is running.
How can I solve that?
Thanks

Hi, @Grokodile thank you for your code. So I commented your code here, Should I put my job logic code where I commented below? Thans

    using System;
using System.ComponentModel;
using System.Threading;
using System.Windows;
using System.Windows.Threading;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private BackgroundWorker _worker;

        public MainWindow()
        {
            InitializeComponent();
        }

        private void RunButtonClickHandler(object sender, RoutedEventArgs e)
        {
            _worker = new BackgroundWorker {WorkerSupportsCancellation = true};
            _worker.DoWork += BackgroundWorkerTask;
            _worker.RunWorkerAsync();
　　　　　　　//I should Put my job logic here, right?
        }

        private void StopButtonClickHandler(object sender, RoutedEventArgs e)
        {
            if (_worker != null && _worker.IsBusy) _worker.CancelAsync();
             //I should Put my job logic here, right?

        }

        private void BackgroundWorkerTask(object sender, DoWorkEventArgs e)
        {
            // this runs on the BackgroundWorker thread.

            while (_worker.CancellationPending == false)
            {
                Thread.Sleep(500);
                //  You have to use the Dispatcher to transfer the effects of
                //  work done in the worker thread back onto the UI thread.
                Dispatcher.BeginInvoke(new Action(UpdateTime), DispatcherPriority.Normal, null);
            }
        }

        private void UpdateTime()
        {
            // Dispatcher runs this on the UI thread.

            timeTextBlock.Text = DateTime.Now.ToString();
        }
    }
}

Answer 1

Futher to what H.B. and dowhilefor have said, here is a sample that shows starting a task on a background thread using BackgroundWorker with one Button and ending it with another Button, note the use of Dispatcher.BeginInvoke:

XAML

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow"
        Height="80"
        Width="640"
        FontSize="16">
    <DockPanel VerticalAlignment="Center">
        <Button Margin="10,0"
                x:Name="runButton"
                DockPanel.Dock="Left"
                Click="RunButtonClickHandler">Run</Button>
        <Button Margin="10,0"
                x:Name="stopButton"
                DockPanel.Dock="Left"
                Click="StopButtonClickHandler">Stop</Button>
        <TextBlock Margin="10,0">The Time Is Now:</TextBlock>
        <TextBlock x:Name="timeTextBlock"
                   Margin="10,0" />
    </DockPanel>
</Window>

Code Behind

using System;
using System.ComponentModel;
using System.Threading;
using System.Windows;
using System.Windows.Threading;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private BackgroundWorker _worker;

        public MainWindow()
        {
            InitializeComponent();
        }

        private void RunButtonClickHandler(object sender, RoutedEventArgs e)
        {
            _worker = new BackgroundWorker {WorkerSupportsCancellation = true};
            _worker.DoWork += BackgroundWorkerTask;
            _worker.RunWorkerAsync();
        }

        private void StopButtonClickHandler(object sender, RoutedEventArgs e)
        {
            if (_worker != null && _worker.IsBusy) _worker.CancelAsync();
        }

        private void BackgroundWorkerTask(object sender, DoWorkEventArgs e)
        {
            // this runs on the BackgroundWorker thread.

            while (_worker.CancellationPending == false)
            {
                Thread.Sleep(500);
                //  You have to use the Dispatcher to transfer the effects of
                //  work done in the worker thread back onto the UI thread.
                Dispatcher.BeginInvoke(new Action(UpdateTime), DispatcherPriority.Normal, null);
            }
        }

        private void UpdateTime()
        {
            // Dispatcher runs this on the UI thread.

            timeTextBlock.Text = DateTime.Now.ToString();
        }
    }
}

EDIT – A Little More Explanation

RunButtonClickHandler

Creates and initializes a BackgroundWorker so that it supports cancellation.
Attaches a DoWorkEventHandler to the DoWork event, i.e. BackgroundWorkerTask.
Starts excecution of the background operation with the call to RunWorkerAsync, i.e. creates a new thread (actually it uses a thread from the thread pool) and runs the code in BackgroundWorkerTask on that thread.

BackgroundWorkerTask

If you want to do work that would otherwise cause the UI to freeze when running on the main UI thread (e.g. search for undiscovered prime numbers) then you do it here in the background thread.

UpdateTime

All WPF Controls inherit from DispatcherObject and are associated with a Dispatcher which manages the execution of work done in the UI’s single thread. If you need to do work such as setting the text of a TextBlock, you can’t do it from the background thread, trying to do so will cause an exception to be thrown. UpdateTime is queued back onto the UI thread by the Dispatcher when Dispatcher.BeginInvoke is called from BackgroundWorkerTask. This way you can get the results of work done in the background before cancelling the background threads execution.

StopButtonClickHandler

Changes _worker.CancellationPending to true with the call to CancelAsync causing the while loop to exit and thus for execution to leave the BackgroundWorkerTask event handler.

In short, you can do work in two places, either in BackgroundWorkerTask or in UpdateTime, but you can only carry out changes to UI elements from UpdateTime.