How to set DefaultValueAttribute of the PropertyGrid dynamically or at runtime?

问题

I am defining a custom class to be used with the PropertyGrid control. Say, one of the properties is defined as such:

[CategoryAttribute("Section Name"),
DefaultValueAttribute("Default value"),
DescriptionAttribute("My property description")]
public string MyPropertyName
{
    get { return _MyPropertyName; }
    set { _MyPropertyName = value; }
}

private string _MyPropertyName;

As you see DefaultValueAttribute defines a default value for the property. Such default value is used in two cases:

If this property value is changed from the default one the PropertyGrid control will display it in bold, and
If I call ResetSelectedProperty method of the PropertyGrid, it will apply that default value to a selected cell.

This concept works fine, except one limitation of the DefaultValueAttribute. It accepts only a constant value. So I'm curious, can I set it dynamically, say, from a constructor or later in the code?

EDIT: I was able to find this code that lets me read the DefaultValueAttribute:

AttributeCollection attributes = TypeDescriptor.GetProperties(this)["MyPropertyName"].Attributes;
DefaultValueAttribute myAttribute = (DefaultValueAttribute)attributes[typeof(DefaultValueAttribute)];
string strDefaultValue = (string)myAttribute.Value;

The question is, how do you set it?

回答1:

Finally, I got the answer! I've been running into a bunch of sites showing how to implement ICustomTypeDescriptor and PropertyDescriptor (here's one), which is fine if you want to add literally two pages of code to your 10-line class.

Here's a much faster way. I found a hint here. Bless those who actually post constructive ideas!

So the answer is to provide two methods in your class. One is private bool ShouldSerializePPP() and another one is private void ResetPPP() where PPP is your property name. The former method will be called by the PropertyGrid to determined if the property value was changed from a default one, and the latter method will be called whenever the PropertyGrid item is reset to a default value.

Here's how my class should look with these additions, that will allow to set a default value for a property at a run-time:

[CategoryAttribute("Section Name"),
DescriptionAttribute("My property description")]
public string MyPropertyName
{
    get { return _MyPropertyName; }
    set { _MyPropertyName = value; }
}
private bool ShouldSerializeMyPropertyName()
{
    //RETURN:
    //      = true if the property value should be displayed in bold, or "treated as different from a default one"
    return !(_MyPropertyName == "Default value");
}
private void ResetMyPropertyName()
{
    //This method is called after a call to 'PropertyGrid.ResetSelectedProperty()' method on this property
   _MyPropertyName = "Default value";
}

private string _MyPropertyName;

来源：https://stackoverflow.com/questions/19749678/how-to-set-defaultvalueattribute-of-the-propertygrid-dynamically-or-at-runtime

标签

.net

winforms

reflection

propertygrid