Routed events and dependency properties .NET wrapper confusion
I'm new to WPF and have a confusion about wrapping syntax of routed events and dependency properties I've seen on many sources that routed events and dependency properties are wrapped like this
// Routed Event
public event RoutedEventHandler Click
{
add
{
base.AddHandler(ButtonBase.ClickEvent, value);
}
remove
{
base.RemoveHandler(ButtonBase.ClickEvent, value);
}
}
// Dependency Property
pu开发者_如何学Pythonblic Thickness Margin
{
set { SetValue(MarginProperty, value); }
get { return (Thickness)GetValue(MarginProperty); }
}
I have never seen add / remove / set / get sort of keywords in C#. Are these are part of C# language as Keywords and i never experienced or worked with them because i didn't worked in C# as pro i'm a C++ programmer? If not keywords then how they are handled by compiler if they are not part of C# and how they are working
I'm gonna try to sum it up for you:
Dependency property:
public int MyProperty
{
get { return (int)GetValue(MyPropertyProperty); }
set { SetValue(MyPropertyProperty, value); }
}
// Using a DependencyProperty as the backing store for MyProperty. This enables animation, styling, binding, etc...
public static readonly DependencyProperty MyPropertyProperty =
DependencyProperty.Register("MyProperty", typeof(int), typeof(MyClass), new UIPropertyMetadata(MyDefaultValue));
That's the full syntax, you don't have to memorize it, just use the "propdp" snippet in Visual Studio.
The "get" must return a value of the type it refers to (in my example, int). Whenever you call
int MyVar = MyProperty;
The code inside "get" is evaluated.
The set has a similar mechanism, only you have another keyword: "value" which will be the value you assign to MyVariable:
MyProperty = 1;
Will call the "set" of MyProperty and "value" will be "1".
Now for the RoutedEvents:
In C# (as in C++, correct me if i'm wrong), to subscribe to an event, you do
MyProperty.MyEvent += MyEventHandler;
That will call the "add" --> you're adding a handler to the stack. Now since it is not automatically garbage-collected, and we want to avoid memory leaks, we do:
MyProperty.MyEvent -= MyEventHandler;
So that our object can be safely disposed of when we don't need it anymore. That's when the "remove" expression is evaluated.
Those mechanism allow you to do multiple things on a single "get", a widely used example in WPF would be:
private int m_MyProperty;
public int MyProperty
{
get
{
return m_MyProperty;
}
set
{
if(m_MyProperty != value)
{
m_MyProperty = value;
RaisePropertyChanged("MyProperty");
}
}
}
Which, in a ViewModel that implements INotifyPropertyChanged, will notify the bindings in your View that the property has changed and need to be retrieved again (so they will call the "get")
精彩评论