C# 覆盖 OnValidating 以支持 null 值但破坏数据绑定

Question

I have a CustomTextBox which inherits from TextBox and overwrites the OnValidating method to allow empty strings. CustomTextBox is bound to Property Price in Domain.

public class CustomTextBox
{
    protected override void OnValidating(...)
    {  
       if(Text=="") 
       {
           Text = null;
           return;
       }
       base.OnValidating(e);
    }
}
public class Domain
{
    public System.Nullable<decimale> Price
    { ... }
}

All works well except that this prevents users froming setting Price to null. Text=null; did not propogate to the domain object. Is there a way to reset Price back to null when user clears out the TextBox?

Answer 1

If you are using Binding to propagate values to the domain object, then you should put this logic in the Parse event instead.

// Add binding
var b = new Binding("Text", myDataSource, "BoundProperty");
b.Parse += OnNullableTextBindingParsed;
myTextBox.DataBindings.Add(b);


// Sample parse handler
private void OnNullableTextBindingParsed(object sender, ConverterEventArgs e)
{
    if (e.Value == String.Empty) e.Value = null;
}