WPF Dependency property ,overrideMetaData issue

 

Seems to know，because MyStackPanel2 has  register, so will new a property, _metaMap has no base type's metadata, so if we use ：

 static MyStackPanel2()

        {

            MyStackPanel.IntDataProperty.OverrideMetadata(typeof(MyStackPanel2), new FrameworkPropertyMetadata(9));

            MyStackPanel.MinDateProperty.AddOwner(typeof(MyStackPanel2), new FrameworkPropertyMetadata(DateTime.Now, onMindateChange2));

        }

 

The new metadata will merge basetype's metadata! For attached property, although register’s metaData is only stored at defaultmetaData， _metaMap have no， but overrideMetaData method will add new metadata to _metaMap, and will do merge too.

And,MyStackPanel2 is sub class of MyStackPanel, so the merge will happen, if not sub class ,the merge will not happen either.like the code below:

public partial class UserControlLabel : Label

{

static UserControlLabel()

        {

            MyStackPanel.MinDateProperty.OverrideMetadata(typeof(UserControlLabel), new FrameworkPropertyMetadata(DateTime.Now, onMinDateChangeUserControl));

 }

        public DateTime MinDate

        {

            get { return (DateTime)GetValue(MyStackPanel.MinDateProperty); }

            set { SetValue(MyStackPanel.MinDateProperty, value); }

        }

}

2. 

This PropertyFromName hashtable is mainly use by the xaml->code process

which can be found by analyzing the DependencyProperty.FromName() method using reflector’s “use by” function..

3. attched property register not use overridemetedata, because its ownertype can not be dependencyObject, _metadataMap need to use 

DependencyObjectType.typeId as key.