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

Safe access to the UI (main) thread in WPF

In WPF applications, interacting with the UI thread from a non-UI thread (such as a background thread) can cause exceptions and crashes. This is because the UI thread has a scheduler that manages updates to the UI and ensures thread safety.

Question:

Consider the following code, which updates a DataGrid when a log file is modified:

<code class="language-c#">private void watcher_Changed(object sender, FileSystemEventArgs e)
{
    if (File.Exists(syslogPath))
    {
        ...
        DGAddRow(crp.Protocol, ft);
    }
}</code>

The DGAddRow method adds a new row to the DataGrid, which must be done on the UI thread. However, since watcher_Changed executes on a background thread, it attempts to modify the UI directly, causing an exception.

Solution:

To safely access the UI thread, use the Dispatcher.Invoke method of Application or any UIElement. This method allows you to execute code on the UI thread.

<code class="language-c#">Application.Current.Dispatcher.Invoke(new Action(() => {
    DGAddRow(crp.Protocol, ft);
}));</code>

By using Dispatcher.Invoke, the code that updates the UI will be executed on the main thread, thus avoiding potential threading issues.

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