WinForms标签前色更新

Question

I've a problem: I try to update font color in a label from another thread, but it fails and I've no idea why.

    private Color defaultBgColor = Color.Red;
    private Color passOkBgColor = Color.LightGreen;

    private Color defaultForeColor = Color.FromArgb(255, 255, 255, 255);
    private Color passOkForeColor = Color.FromArgb(255, 0, 0, 255);

There's my function:

private void Func() {
        try {
            if ( pipeReader != null) {
                string msg_strg = String.Empty;
                while(true) {
                    if ( !npsc.IsConnected ) {
                        npsc.Connect();
                        Thread.Sleep(500);
                        continue;
                    }

                    while ( (msg_strg = pipeReader.ReadLine()) != null ) {                      ;
                        statusLabel.BeginInvoke( (MethodInvoker)(() => {
                                                                    if ( statusesDict.ContainsKey(msg_strg) )
                                                                        statusLabel.Text = statusesDict[msg_strg];
                                                                    else
                                                                        statusLabel.Text = "!UNKNOWN STATUS!";

                                                                    if ( msg_strg != "CARDREADER_USER_EXISTS" ) {
                                                                        this.BackColor = defaultBgColor;
                                                                        statusLabel.ForeColor = defaultForeColor;
                                                                    } else {
                                                                        this.BackColor = passOkBgColor;
                                                                        statusLabel.ForeColor = passOkForeColor;
                                                                    }
                                                                 }) );
                        statusLabel.Refresh();
                        Thread.Sleep(300);
                    }
                }
            }
        } catch ( Exception ex ) {
            Log.Instance.Error("Exception: "+ex.Message);
        }
    }

How should I resolve this problem?

Answer 1

There are at least two issues with your code.

First, statusLabel.Refresh call should be inside the BeginInvoke block.

Second, the BeginInvoke block is using captured variable msg_strg which might have been modified at the time the block executes.

The following will fix the above issues, try and see if your problem (whatever it is) is solved:

private void Func() {
    try {
        if (pipeReader != null) {
            Action<string> updateStatus = message =>
            {
                if (statusesDict.ContainsKey(message))
                    statusLabel.Text = statusesDict[message];
                else
                    statusLabel.Text = "!UNKNOWN STATUS!";

                if (message != "CARDREADER_USER_EXISTS") {
                    this.BackColor = defaultBgColor;
                    statusLabel.ForeColor = defaultForeColor;
                } else {
                    this.BackColor = passOkBgColor;
                    statusLabel.ForeColor = passOkForeColor;
                }

                statusLabel.Refresh();
            };


            while(true) {
                if (!npsc.IsConnected) {
                    npsc.Connect();
                    Thread.Sleep(500);
                    continue;
                }

                string msg_str;
                while ((msg_strg = pipeReader.ReadLine()) != null) {
                    statusLabel.BeginInvoke(updateStatus, msg_str);
                    Thread.Sleep(300);
                }
            }
        }
    } catch (Exception ex) {
        Log.Instance.Error("Exception: " + ex.Message);
    }
}