Question

我有一个按钮，按下该按钮可获取远程PC上各种Windows服务的状态。我想每分钟自动刷新此按钮，以便始终显示服务的最新状态。

我试图设置一个计时器，但我一直收到错误＆＃34;跨线程操作无效：控制＆＃39; btnRefreshServices＆＃39;从在＆＃34;

上创建的线程以外的线程访问

任何帮助表示赞赏

    private void btnRefreshServices_Click(
        object sender,
        EventArgs eventArgs)
    {
        this.btnRefreshServices.Enabled = false;

        // Setting up progress bar in a separate thread to update the progress bar
        // This is necessary so that the dialog doesn't freeze while the progress bar is reporting its progress
        this.prgbServiceStatus.Minimum = 1;
        this.prgbServiceStatus.Maximum = 11;
        this.prgbServiceStatus.Step = 1;
        this.prgbServiceStatus.Value = 1;
        this.prgbServiceStatus.Increment(1);
        this.prgbServiceStatus.PerformStep();

        var _backgroundWorker = new BackgroundWorker();
        _backgroundWorker.ProgressChanged += ProgressChanged;
        _backgroundWorker.DoWork += DoWork;
        _backgroundWorker.WorkerReportsProgress = true;
        _backgroundWorker.RunWorkerAsync();
        _backgroundWorker.RunWorkerCompleted += new  RunWorkerCompletedEventHandler(RunWorkerCompleted);
    }

    private void DoWork(
        object sender,
        DoWorkEventArgs doWorkEventArgs)
    {
        // Get the current status of each Windows service and reflect the progress in the progress bar
        // NOTE: If you add a new service, divide the number of services by 100 and update each call to report progress
        ((BackgroundWorker)sender).ReportProgress(15);

        CurrentStatus(
            this.grdResults,
            ServerA,
            ServiceName,
            RowIndexA);
        ((BackgroundWorker)sender).ReportProgress(25);

        CurrentStatus(
            this.grdResults,
            ServerB,
            ServiceNameB,
            RowIndexB);
        ((BackgroundWorker)sender).ReportProgress(35);

}

我正在使用类似于此代码的计时器

    Timer myTimer = new Timer();
    myTimer.Elapsed += new ElapsedEventHandler(DisplayTimeEvent);
    myTimer.Interval = 1000; // 1000 ms is one second
    myTimer.Start();

    public static void DisplayTimeEvent(object source, ElapsedEventArgs e)
    {
       // code here will run every second
    }

使用Emile Pels代码我能够解决我的问题。

    public frmServicesManager()
    {
        InitializeComponent();

        // The interval in milliseconds (1000 ms = 1 second)
        const double interval = 5000.0;

        // Create a new timer
        new System.Timers.Timer()
            {
                Enabled = true,
                Interval = interval
            }.Elapsed += TimerCallback;
    }

    private void TimerCallback(
        object sender, 
        ElapsedEventArgs elapsedEventArgs)
    {
        // SignalTime is now of type DateTime and contains the value indicating when the timer's Elapsed event was raised
        var _signalTime = elapsedEventArgs.SignalTime;

        // Create a new Action
        var _setButtonClick = new Action<DateTime>(dateTime => this.btnRefreshServices.PerformClick());

        // Check if we can access the control from this thread
        if (this.btnRefreshServices.InvokeRequired)
        {
            // We can't access the label from this thread,so we'll call invoke so it is executed from the thread the it was created on
            this.btnRefreshServices.Invoke(_setButtonClick, _signalTime);
        }
    }

Answer 1

使用System.Windows.Forms.Timer，或者从另一个线程设置按钮的属性，如下所示：

myButton.Invoke(new Action<string>((text) => myButton.Text = text), "New button text");

编辑：这是一个有更多解释的例子。

您收到该错误的原因是您正在尝试访问在其他线程上创建的控件，这将无效。您必须调用控件的Invoke()方法;执行您在创建控件的线程上传递的委托。您可以使用的其中一位代表是Action，我将在本文后面进行演示。

对于以下示例，我使用了System.Timers.Timer，并创建了一个新的Winforms项目，并仅向其添加了Label。它的名字是timeLabel。

我将此代码放在我的表单构造函数中：

//The interval in milliseconds (1000 ms = 1 second)
const double interval = 1000.0;

//Create a new timer
new System.Timers.Timer()
{
    Enabled = true, //Start it right away
    Interval = interval //Set the interval
}.Elapsed += TimerCallback; //Register a handler for the elapsed event

这将创建一个新的计时器并注册一个回调来处理其Elapsed事件，该事件的定义如下：

private void TimerCallback(object sender, System.Timers.ElapsedEventArgs e)
{
    const string baseString = "The event was raised at {0}";

    //signalTime is now of type DateTime and contains the value 
    //indicating when the timer's Elapsed event was raised
    var signalTime = e.SignalTime;

    //Create a new Action - delegate - which takes a string argument
    var setLabelText = new Action<DateTime>(dt =>
    {
        //If the amount of seconds in the dt argument is an even number,
        //set the timeLabel's forecolor to red; else, make it green
        timeLabel.ForeColor = dt.Second % 2 == 0 ? Color.Red : Color.Green;

        //Format the baseString to display the time in dt
        timeLabel.Text = string.Format(baseString, dt.ToLongTimeString());
    });

    //Check if we can access the control from this thread
    if (timeLabel.InvokeRequired) {
        //We can't access the label from this thread,
        //so we'll call invoke so it is executed from
        //the thread the it was created on
        timeLabel.Invoke(setLabelText, signalTime);
    }
    else {
        //The label's text can be set from this thread,
        //we'll just call the delegate without Invoke()
        setLabelText(signalTime);
    }
}

此特定示例每秒将标签的文本更改为当前时间，如果秒数为偶数，则会使标签的前景色为红色：当它为奇数时，颜色将设置为绿色。该程序可能看起来不是很有用，但它演示了如何从其他线程访问控件;一旦你掌握了这个例子，它应该帮助你扩展它以满足你的需要。

Answer 2

我不清楚所有BackgroundWorker代码与您的问题有什么关系。它似乎与跨线程问题没有任何关系，也没有定期刷新按钮。

就问题的确如此，您应该能够使用正确的Timer类（.NET中至少有三个），System.Windows.Forms.Timer。在这种情况下，您的代码看起来像这样：

System.Windows.Forms.Timer myTimer = new System.Windows.Forms.Timer();
myTimer.Tick += DisplayTimeEvent;
myTimer.Interval = 1000; // 1000 ms is one second
myTimer.Start();

public static void DisplayTimeEvent(object source, EventArgs e)
{
   // code here will run every second
}

上面的代码应该在Winforms模块中，因此System.Windows.Forms命名空间应该已经在范围内了，但为了清楚起见，我已经完全限定了上面的Timer类名。

另请注意，事件名称不同：Tick而非Elapsed。事件处理程序签名略有不同。

使用此Timer类而不是您正在使用的类，将在UI线程上调用Tick事件处理程序，完全避免任何跨线程问题。

以指定的时间间隔运行方法c＃

2 个答案: