WPF Dispatcher非同步應用(防止介面無反應)－天天向上

MainWindow.xaml

   1: <Window x:Class="WpfDispatcherApp.MainWindow"   2:         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"   3:         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"   4:         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"   5:         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"   6:         xmlns:local="clr-namespace:WpfDispatcherApp"   7:         mc:Ignorable="d"   8:         Title="MainWindow" Height="137" Width="554">   9:     <UniformGrid Rows="3" Columns="2">  10:         <Label Content="Input a number:" Height="28" HorizontalAlignment="Center" Name="label1" VerticalAlignment="Center" />  11:         <TextBox Height="23" HorizontalAlignment="Center" Name="textBox1" VerticalAlignment="Center" Width="100" Text="1000000000"/>  12:    13:         <Label Content="Result:" Height="28" HorizontalAlignment="Center" Name="label2" VerticalAlignment="Center" />  14:         <TextBox Height="23" HorizontalAlignment="Center" Name="textBox2" VerticalAlignment="Center" Width="100"/>  15:         <Button Content="synchronization" Height="23" HorizontalAlignment="Center" Name="button1" VerticalAlignment="Center" Width="100" Click="button1_Click" />  16:         <Button Content="asynchronization" Height="23" HorizontalAlignment="Center" Name="button2" VerticalAlignment="Center" Width="100" Click="button2_Click" />  17:     </UniformGrid>  18: </Window>

button1_Click 同步執行

   1: private void button1_Click(object sender, RoutedEventArgs e)   2: {   3:     Int64 inputNumber;   4:     Int64.TryParse(this.textBox1.Text, out inputNumber);   5:     this.textBox2.Text = "";   6:     7:     Thread thread = new Thread(new ParameterizedThreadStart(SyncCallback));   8:     thread.Start(inputNumber);   9: }

button1開一個執行緒執行回呼函式SyncCallback

   1: private void SyncCallback(object inputNumber)   2: {   3:     this.Dispatcher.BeginInvoke((Action)delegate ()   4:     {   5:         this.textBox2.Text = TimesTwo((Int64)inputNumber).ToString();   6:     });   7: }

在TimesTwo()模擬一個需要5秒模擬時間

   1: private double TimesTwo(Int64 inputNumber)   2: {   3:     // 模擬大量計算等待時間   4:     Thread.Sleep(5000);   5:     return 2 * inputNumber;   6: }

上面回呼函式SyncCallback中

BeginInvoke 是非同步執行，但是TimesTwo計算未完成前，介面自然會被卡住this.textBox2

所以，按下button1滑鼠去移動GUI會發現無反應。

   1: this.Dispatcher.BeginInvoke((Action)delegate ()   2: {   3:  this.textBox2.Text = TimesTwo((Int64)inputNumber).ToString();   4: });

解決方式

將SyncCallback內容修改成AsyncCallback

   1: private void AsyncCallback(object inputNumber)   2: {   3:    double result = TimesTwo((Int64)inputNumber);          4:    this.Dispatcher.BeginInvoke((Action)delegate ()   5:    {              6:        this.textBox2.Text = result.ToString();   7:    });         8: }

由上面程式碼可以看出，TimesTwo 未計算完成前，會另外開非同步呼叫(BeginInvoke)

this.textBox2更新，防止AsyncCallback執行緒因為Timestwo未計算完成而被堵塞，

直到計算Timestwo完成時，再去更新this.textBox2.Text，

所以在TimesTwo計算期間，介面可以自由移動，非同步執行更新this.textBox2.Text

非同步應用: 更新即時影像串流事件Callback

必須加上

this.Dispatcher.BeginInvoke((Action)delegate(){ … });

才能避免MainWindow介面被咬死或是應用程式無反應

   1: public void FrameGrabbed(int cameraIndex, double frameCount)   2: {   3:    this.Dispatcher.BeginInvoke((Action)delegate()   4:    {   5:        try   6:        {   7:            bool flag = cVideo.Snap(cameraIndex);   8:            if (!flag)   9:            {  10:                videoTimer.StopPlayBtn_Click(null, null);  11:                return;  12:            }  13:            videoPgBar.Value = frameCount;  14:    15:            // if frameCount equals to the maximum value of the video  16:            if (videoPgBar.Maximum == frameCount)  17:                videoTimer.StopPlayBtn_Click(null, null);  18:    19:            //cVideo.PutTextOfFrameCount(cameraIndex);  20:            cVideo.ShowLiveImage(cameraIndex);  21:        }  22:        catch (Exception)  23:        {  24:            videoTimer.StopPlayBtn_Click(null, null);  25:        }  26:    });  27:    28: }