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name: threading-wpf-dispatcher description: Explains WPF Dispatcher priority system and threading patterns. Use when implementing background operations, maintaining UI responsiveness, or understanding task scheduling order.

WPF Dispatcher Threading

Priority Levels (High to Low)

Common Patterns

Background Work (UI Responsive)

Copyawait Dispatcher.InvokeAsync(() =>
{
    // This runs between input processing
    ProcessNextChunk();
}, DispatcherPriority.Background);

After Render Complete

Copyawait Dispatcher.InvokeAsync(() =>
{
    // Runs after layout/render
    ScrollIntoView(lastItem);
}, DispatcherPriority.Loaded);

Idle Cleanup

CopyDispatcher.InvokeAsync(() =>
{
    // Low priority cleanup
    ClearUnusedCache();
}, DispatcherPriority.ApplicationIdle);

Yielding Pattern

Keep UI responsive during long operations:

Copypublic async Task ProcessLargeDataAsync(IList<Item> items)
{
    for (int i = 0; i < items.Count; i++)
    {
        Process(items[i]);

        // Yield every 100 items to process pending input
        if (i % 100 == 0)
        {
            await Dispatcher.Yield(DispatcherPriority.Background);
            UpdateProgress(i, items.Count);
        }
    }
}

Threading Rules

Copy// Check if on UI thread
if (!Dispatcher.CheckAccess())
{
    Dispatcher.Invoke(() => UpdateUI());
    return;
}

// From background thread
await Task.Run(() =>
{
    var result = HeavyComputation();

    // Marshal back to UI
    Dispatcher.Invoke(() => DisplayResult(result));
});

Avoid

Copy// ❌ Send priority - can cause deadlock
Dispatcher.Invoke(() => {}, DispatcherPriority.Send);

// ❌ Blocking UI thread
Thread.Sleep(1000);

// ✅ Use async/await instead
await Task.Delay(1000);