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;
    }
}