WPF Memory Optimization

1. Freezable Pattern

Why Freeze?

Benefit Description

Thread-safe Can be used across threads

No change tracking Reduces overhead

Renderer optimization Better GPU utilization

Basic Usage

// Always freeze static resources var brush = new SolidColorBrush(Colors.Red); brush.Freeze();

var pen = new Pen(Brushes.Black, 1); pen.Freeze();

XAML Freeze

<Window xmlns:po="http://schemas.microsoft.com/winfx/2006/xaml/presentation/options" mc:Ignorable="po"> <Window.Resources> <SolidColorBrush x:Key="FrozenBrush" Color="Red" po:Freeze="True"/> </Window.Resources> </Window>

When Freeze Fails

if (brush.CanFreeze) brush.Freeze(); else // Has bindings or animations - cannot freeze

Modifying Frozen Objects

var clone = frozenBrush.Clone(); // Creates unfrozen copy clone.Color = Colors.Blue; clone.Freeze(); // Freeze again if needed

2. Common Memory Leaks

Event Handler Leaks

// ❌ LEAK: Static event holds reference SomeStaticClass.StaticEvent += OnEvent;

// ✅ FIX: Unsubscribe in Unloaded Unloaded += (s, e) => SomeStaticClass.StaticEvent -= OnEvent;

CompositionTarget.Rendering Leak

// ❌ LEAK: Never unsubscribed CompositionTarget.Rendering += OnRendering;

// ✅ FIX: Always unsubscribe Loaded += (s, e) => CompositionTarget.Rendering += OnRendering; Unloaded += (s, e) => CompositionTarget.Rendering -= OnRendering;

Binding Without INotifyPropertyChanged

// ❌ LEAK: PropertyDescriptor retained public string Name { get; set; } // No INPC

// ✅ FIX: Implement INPC public string Name { get => _name; set { _name = value; OnPropertyChanged(); } }

DispatcherTimer Leak

// ❌ LEAK: Timer keeps running _timer = new DispatcherTimer(); _timer.Tick += OnTick; _timer.Start();

// ✅ FIX: Stop and cleanup Unloaded += (s, e) => { _timer.Stop(); _timer.Tick -= OnTick; };

Image Resource Leak

// ❌ LEAK: Stream kept open var bitmap = new BitmapImage(new Uri(path));

// ✅ FIX: Load immediately and release stream var bitmap = new BitmapImage(); bitmap.BeginInit(); bitmap.CacheOption = BitmapCacheOption.OnLoad; bitmap.UriSource = new Uri(path); bitmap.EndInit(); bitmap.Freeze();

3. Diagnostic Checklist

Code Review Points

• All static event subscriptions have unsubscribe logic

• CompositionTarget.Rendering unsubscribed in Unloaded

• DispatcherTimer stopped in Unloaded

• ViewModels implement INotifyPropertyChanged

• Images use BitmapCacheOption.OnLoad

• Static resources are Frozen

Diagnostic Tools

Tool Purpose

VS Diagnostic Tools Real-time memory snapshots

dotMemory Detailed retention paths

PerfView GC and allocation analysis

Memory Monitor

public static class MemoryMonitor { public static void LogMemory(string context) { GC.Collect(); GC.WaitForPendingFinalizers(); GC.Collect();

    var mem = GC.GetTotalMemory(true) / 1024.0 / 1024.0;
    Debug.WriteLine($"[{context}] Memory: {mem:F2} MB");
}

}

4. Resource Factory Pattern

public static class FrozenResources { public static SolidColorBrush CreateBrush(Color color) { var brush = new SolidColorBrush(color); brush.Freeze(); return brush; }

public static Pen CreatePen(Color color, double thickness)
{
    var pen = new Pen(CreateBrush(color), thickness);
    pen.Freeze();
    return pen;
}

}