System.Timers.Timer 的使用

 

.Net framwork 提供了許多 Time 方法可以使用，分別是

System.Timers.Timer

System.Threading.Timer

System.Windows.Forms.Timer

System.Windows.Threading.DispatcherTimer

在某種程度上用法其實是大同小異的

 

UI code

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApplication1"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525" Loaded="Window_Loaded">
    <Grid Margin="10">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="39*"/>
            <ColumnDefinition Width="22*"/>
        </Grid.ColumnDefinitions>
        <Button x:Name="button" Content="Button" Margin="15,15,10,10" Grid.Column="1" Click="button_Click"/>
        <Label x:Name="label" Content="秒數倒數" Margin="10"/>
    </Grid>
</Window>

後端Code

using System;
using System.Timers;
using System.Windows;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        Timer Timer = new Timer();
        int CountDown = 0;

        public MainWindow()
        {
            InitializeComponent();
        }

        private void button_Click(object sender, RoutedEventArgs e)
        {
            CountDown = 3;
            label.Content = CountDown;
            Timer.Start();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            try
            {
                Timer.Interval = 1000;
                Timer.Elapsed += new System.Timers.ElapsedEventHandler(TimerTick);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }

        private void TimerTick(object sender, System.Timers.ElapsedEventArgs e)
        {
            try
            {
                if (CountDown > 0)
                {
                    CountDown--;
                    label.Content = CountDown;
                }
                else
                {
                    Timer.Stop();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }
    }
}

此範例為秒數倒數程式，當執行倒數時你會發現

「呼叫執行緒無法存取此物件 因為此物件屬於另一個執行緒。」錯誤，

因為在WPF、WinForm這些應用程式中，必需是UI執行緒才能控制表單，

所以說非UI執行緒如果要控制表單，如上例TimerTick(object sender, System.Timers.ElapsedEventArgs e)，

必須要將控制表單的程式邏輯封裝成為委派，再將這個委派提交給UI執行緒去執行，

藉由這個流程非UI執行緒就能夠跨執行緒控制表單。

改成如下

using System;
using System.Timers;
using System.Windows;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        Timer Timer = new Timer();
        int CountDown = 0;

        public MainWindow()
        {
            InitializeComponent();
        }

        private void button_Click(object sender, RoutedEventArgs e)
        {
            CountDown = 3;
            label.Content = CountDown;
            Timer.Start();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            try
            {
                Timer.Interval = 1000;
                Timer.Elapsed += new System.Timers.ElapsedEventHandler(TimerTick);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }

        private void TimerTick(object sender, System.Timers.ElapsedEventArgs e)
        {
            try
            {
                if (CountDown > 0)
                {
                    CountDown--;
                    Action methodDelegate = delegate ()
                    {
                        label.Content = CountDown;
                    };
                    this.Dispatcher.BeginInvoke(methodDelegate);
                }
                else
                {
                    Timer.Stop();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }
    }
}

值得注意的是，System.Timers.Timer於跨執行緒更新UI的方式除了上述的委派方式之外，

還可以使用SynchronizingObject屬性來達成，程式碼改成如下

private void Window_Loaded(object sender, RoutedEventArgs e)
{
    try
    {
        Timer.Interval = 1000;
        Timer.Elapsed += new System.Timers.ElapsedEventHandler(TimerTick);
        this.Timer.SynchronizingObject = this;
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString());
    }
}

但是這會發生「CS0266 Cannot implicitly convert type

'WpfApplication1.MainWindow' to 'System.ComponentModel.ISynchronizeInvoke'.

An explicit conversion exists (are you missing a cast?)」錯誤，

原因為這種方式只適用在WinForm並不適合用在WPF，

詳細說明可參考WPF window doesn't implement ISynchronizeInvoke.InvokeRequired ERROR

 

參考資料：

[WPF] 跨執行緒控制表單

Timer Class