How Can I Safely Update a WPF UI from a Background Thread?

Thread-Safe WPF UI Updates: A Practical Guide

WPF applications require careful handling of UI updates from background threads. Directly accessing UI elements from a background thread is unsafe and can cause application instability or crashes. This is because UI elements are inherently bound to the main application thread.

Let's consider a scenario where a file system watcher updates a data grid with log file entries. Attempting to add a new row directly (e.g., dataGridRows.Add(ds)) within the watcher's event handler on a background thread is incorrect.

The solution lies in using the Dispatcher class. The Dispatcher provides a mechanism to marshal code execution to the main thread, ensuring thread safety. The Dispatcher.Invoke method is key here.

Here's how you can modify the watcher_Changed event handler to safely update the data grid:

private void watcher_Changed(object sender, FileSystemEventArgs e)
{
    if (File.Exists(syslogPath))
    {
        string line = GetLine(syslogPath, currentLine);
        foreach (CommRuleParser crp in crpList)
        {
            FunctionType ft = new FunctionType();
            if (crp.ParseLine(line, out ft))
            {
                Application.Current.Dispatcher.Invoke(() => DGAddRow(crp.Protocol, ft));
            }
        }
        currentLine++;
    }
    else
    {
        MessageBox.Show(UIConstant.COMM_SYSLOG_NON_EXIST_WARNING);
    }
}

By using Application.Current.Dispatcher.Invoke, the DGAddRow method is executed on the main thread. This guarantees safe access to the data grid and prevents threading conflicts. This approach ensures that all UI updates are handled correctly and prevents potential crashes or unpredictable behavior.

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