Ninject conditional binding based on property value

Question

I am having trouble defining bindings using ninject.

I am in a standard ASP.NET WebForms application. I have defined an http handler to Inject dependencies in pages

Answer 1

A conditional binding based on a property value isn't a good design and isn't even possible (at least for constructor injection) as dependencies are normally created before the object receiving them. What if the property is changed later? The preferable way is to inject a factory or factory method that requests the instance from Ninject and exchange the strategy on initialization and property value change internally.

public enum EntityType { A,B } 
public class MyControl : UserControl
{
    [Inject]
    public Func DisplayStrategyFactory 
    { 
        get { return this.factory; }
        set { this.factory = value; this.UpdateEntityDisplayStrategy(); }
    }

    public EntityType Type 
    { 
        get { return this.type; } 
        set { this.type = value; this.UpdateEntityDisplayStrategy(); };
    }

    private UpdateEntityDisplayStrategy()
    {
        if (this.DisplayStrategyFactory != null)
            this.entityDisplayStrategy = this.DisplayStrategyFactory(this.type);
    }
}

Bind>
    .ToMethod(ctx => type => 
         type == ctx.kernel.Get( m => 
             m.Get("EntityType", EntityType.A));
Bind.To()
    .WithMetadata("EntityType", EntityType.A)
Bind.To()
    .WithMetadata("EntityType", EntityType.B)

Alternatively add an activation action and inject the dependency manually. But be aware that changing the constraint property will lead to an inconsistent state.

OnActivation((ctx, instance) => 
    instance.MyStrategy = ctx.Kernel.Get(m => 
        m.Get("MyConstraint", null) == instance.MyConstraint);