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Flyweight Pattern

Flyweight Pattern 


Gamma Categorization: Structural Design Pattern
Summary:Use sharing to support large numbers of fine-grained objects efficiently.

Sample Code

Problem: We want to store in memory only one object per unique filter definition.

Code

public class Filter
{
    public Guid ID { get; set; }
    public List<string> FilterProperties { get; set; } = new List<string>();

    public bool Equals(Filter filter)
    {
        if(this.FilterProperties.Count != filter.FilterProperties.Count)
            return false;

        this.FilterProperties.Sort();
        filter.FilterProperties.Sort();

        if (!this.FilterProperties.SequenceEqual(filter.FilterProperties))
            return false;

        return true;
    }
}

public class PhotoEditor
{
    private List<Filter> filterCache = new List<Filter>();
    private Dictionary<string,Guid> filters = new Dictionary<string, Guid>();

    public void ApplyFilter(string filterName)
    {
        if(!filters.ContainsKey(filterName))
            return;

        var filterGuid = filters[filterName];
        var filter = filterCache.FirstOrDefault(f => f.ID == filterGuid);

        System.Console.WriteLine($"\nFilter Name: {filterName}");
        System.Console.WriteLine($"Internal Filter ID: {filterGuid}");

        filter.FilterProperties.ForEach(p => System.Console.WriteLine($"\tApplying {p}"));
    }

    public void AddFilter(string filterName, List<string> filterProperties)
    {
        var newFilter = new Filter { ID = Guid.NewGuid(), FilterProperties = filterProperties };

        Guid existingFilterGuid = Guid.Empty;
        foreach (var filter in filterCache)
        {
            if(filter.Equals(newFilter))
            {
                existingFilterGuid = filter.ID;
                break;
            }
        }

        if(existingFilterGuid != Guid.Empty)
            filters.Add(filterName, existingFilterGuid);
        else
        {
            filterCache.Add(newFilter);
            filters.Add(filterName, newFilter.ID);
        }
    }
}

Usage

photoEditor.AddFilter("Preset1", new List<string> { "Contrast" });
photoEditor.AddFilter("Preset2", new List<string> { "Contrast", "Sharpen", "Saturation", "White balance"});
photoEditor.AddFilter("Preset3", new List<string> { "Contrast", "Sharpen", "Saturation", "White balance"});
photoEditor.AddFilter("Preset4", new List<string> { "Saturation" });
photoEditor.AddFilter("Preset5", new List<string> { "Contrast" });

photoEditor.ApplyFilter("Preset1");
photoEditor.ApplyFilter("Preset2");
photoEditor.ApplyFilter("Preset3");
photoEditor.ApplyFilter("Preset4");
photoEditor.ApplyFilter("Preset5");

Output

Filter Name: Preset1
Internal Filter ID: 8d056cb7-9f78-498f-a692-57dfa0674d16
        Applying Contrast

 Filter Name: Preset2
Internal Filter ID: eb0b6b2d-b4ed-43d1-b46b-b1a8ad06cd53
        Applying Contrast
        Applying Saturation
        Applying Sharpen
        Applying White balance

 Filter Name: Preset3
Internal Filter ID: eb0b6b2d-b4ed-43d1-b46b-b1a8ad06cd53
        Applying Contrast
        Applying Saturation
        Applying Sharpen
        Applying White balance

 Filter Name: Preset4
Internal Filter ID: 11ed980b-902a-4e0d-8d9b-05e6908ea2d3
        Applying Saturation

 Filter Name: Preset5
Internal Filter ID: 8d056cb7-9f78-498f-a692-57dfa0674d16
        Applying Contrast

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