单击时更改文本块文本

Question

I have a <Border> inside that I have an <Image> and a <Textblock> , and I am trying to change the textblock text on Mouseleftbutton down, since there is some more lengthy operation inside this click event, text of text block doesn't change till this operation get completed.

also I tried Dispatcher.BeginInvoke() , but no success.

Here is my Code :

<Border x:Name="btnReadMe" Grid.Row="0" Style="{StaticResource BorderStyle1}" MouseLeftButtonDown="btnReadMe_MouseLeftButtonDown" MouseLeftButtonUp="btnReadMe_MouseLeftButtonUp" >
    <Border.Background>
        <LinearGradientBrush StartPoint="0.5,0" EndPoint="0.5,1">
            <GradientStop Color="#46c746" Offset="0"/>
            <GradientStop Color="#129312" Offset="1"/>
        </LinearGradientBrush>
    </Border.Background>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="3*"/>
            <ColumnDefinition Width="6*"/>
        </Grid.ColumnDefinitions>
        <Image Grid.Column="0" Source="/CareFamily.AtHome;component/Resources/read_message-read_it.png" Margin="5,15" >
            <Image.RenderTransform>
                <ScaleTransform ScaleX="1" ScaleY="1"/>
            </Image.RenderTransform>
        </Image>
        <StackPanel Grid.Column="1" Margin="0,10,0,10"  VerticalAlignment="Center">
            <TextBlock Name="tbReadToMe" Text="Read to Me" Style="{StaticResource TextBlockStyle1}" Margin="0,0,0,0"  />
        </StackPanel>
    </Grid>
</Border>

---

SpVoice voice;
private void btnReadMe_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    if (voice == null)
        voice = new SpVoice();


    string readMessageState = tbReadToMe.Text;
    switch (readMessageState)
    {
        case "Read to Me":
            {
                tbReadToMe.Text = "Pause";
                break;
            }

        case "Pause":
            {
                tbReadToMe.Text = "Resume";
                voice.Pause();
                break;
            }

        case "Resume":
            {
                tbReadToMe.Text = "Pause";
                voice.Resume();
                break;
            }
        default:
            {
                tbReadToMe.Text = "Read to Me";
                break;
            }
    }


    if (!string.IsNullOrEmpty(Msg.Subject))
    {
        voice.Speak(Msg.Subject, SpeechVoiceSpeakFlags.SVSFDefault);
    }
    if (!string.IsNullOrEmpty(Msg.Body))
    {
        voice.Speak(Msg.Body, SpeechVoiceSpeakFlags.SVSFDefault); // Length operation
    }
}

Answer 1

Execute your lengthy operation on a Thread and use the

Dispatcher

to update the UI accordingly.

Example Code:

var opThread = new Thread(delegate()
{
    //your lengthy operation

    tbReadToMe.Dispatcher.Invoke(new Action(delegate
    {
        tbReadToMe.Text = "Pause";
    }));

    //your lengthy operation

    tbReadToMe.Dispatcher.Invoke(new Action(delegate
    {
        tbReadToMe.Text = "etc...";
    }));
});

opThread.Start();

Answer 2

The reason Dispatcher.BeginInvoke() didn't help is because even though it operates asycnronously, it still does it on the main/UI thread. Do your lengthy operation on a background thread using the BackgroundWorkerThread class.

I worked up a little sample to demonstrate:

Window1.xaml:

<Window x:Class="BackgroundWorkerExample.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="663">
<Grid>
    <TextBox PreviewMouseDown="textBox1_PreviewMouseDown" Height="38" Margin="24,34,26,0" Name="textBox1" VerticalAlignment="Top" FontSize="24">
        The quick Velociraptor jumped over the torpid tapir.
    </TextBox>
</Grid>

Window1.xaml.cs:

using System.Windows;
using System.Windows.Input;
using System.ComponentModel;
using System.Threading;
using System.Windows.Media;
using System;

namespace BackgroundWorkerExample
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }


        void _asyncSpeakerThread_DoWork(object sender, DoWorkEventArgs e)
        {
            // Change color of text to Red to indicate Start of operation
            this.Dispatcher.BeginInvoke(new Action(() =>  { textBox1.Foreground = Brushes.Red; }));

            string text = e.Argument as string;
            //voice.Speak(text, SpeechVoiceSpeakFlags.SVSFDefault); // Lengthy operation 
            Thread.Sleep(1000); // Simulate lengthy operation

            // Change color of text to Black to indicate End of operation
            this.Dispatcher.BeginInvoke(new Action(() => { textBox1.Foreground = Brushes.Black; }));
        }

        private void textBox1_PreviewMouseDown(object sender, MouseButtonEventArgs e)
        {
            BackgroundWorker bw = new BackgroundWorker();

            bw.DoWork += new DoWorkEventHandler(_asyncSpeakerThread_DoWork);
            string workerArgument = textBox1.Text;
            bw.RunWorkerAsync(workerArgument);
        }
    }
}

Answer 3

在“冗长”操作之前使用Application.DoEvents() ！