C# – WPF Custom Controls Construction,Triggers and Events

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I want to build a new custom control. I found few tutorials that gave me some clue of how to achieve this. As I understand it, creating a new custom control is always done by extending a current one, and it is even possible to extend
a control from the very basic levels of the hierarchy, in example, you can even extend:

  • UIElement
  • FrameworkElement
  • Control
  • ContentControl
  • HeaderedContentControl
  • ItemsControl
  • Selector
  • RangeBase

As written in the following tutorial: http://wpftutorial.net/HowToCreateACustomControl.html

So, I followed the tutorial and created a new project of type Custom Control Library, got my generic .xaml and my code behind. So far so good.

There are 3 types or categories of events I can distinguish between.

  1. Events that are consumable by the window (or container) that will use my control: those are the events I would like to expose to the outside. How to write those?

  2. Events that are related to the control itself and not being exposed outside;
    for example, if the mouse is over my control and I would like to react
    to that. I can do that in the XAML:

    <ControlTemplate.Triggers>
  <Trigger Property="IsMouseOver" Value="true">  
    <Setter Property="Fill" TargetName="LeftTraingularIndicator">  
      <Setter.Value>  
        <SolidColorBrush Color="Yellow" />  
      </Setter.Value>  
    </Setter>
  </Trigger>
</ControlTemplate.Triggers>

Assuming of couse I have an element with the fill property in my
ControlTemplate which is named x:name="LeftTraingularIndicator"

Questions:

Now I want to react in my XAML to IsMouseDown. How do I do that?
There is no "IsMouseDown" Trigger. Furthermore what if I want
to react to that in the code behind? And even further what if I want
to change LeftTraingularIndicator "Fill" from the code behind?

  1. Events that related to sub-elements which are part of the visual
    construction of my ControlTemplate, in example what if I want to react
    to "IsMouseOver" of "LeftTraigularIndicator" in XAML / or even in Code Behind?
    Maybe even both.

I am attempting for 2 days now… feeling I am missing something in my understanding of how things work. Didn't find any tutorial that deeply explains those questions.

I would like to see a few lines of example for each of the questions I surfaced here.

Thanks.

Best Answer

After extensive research...

1) Exposing events to the outside... Simply as if you were exposing from any other class.

public delegate void myDelegate(int someValue);  
public event myDelegate myEvent;

and somewhere in your code:

if(myEvent!=null)
  myEvent(5);

Nothing new in that part.

2) From the code behind create an instance constructor

public MyCustomControl()
{
    MouseMove += MyCustomControl_MouseMove;
}


void MyCustomControl_MouseMove(object sender, MouseEventArgs e)
{
   //now you can react to the movement of the mouse.
   //if for example I want to address an element, let's say a rectangle:

   var ele = (Rectangle)Template.FindName("myRect",this);
   ele.Fill=myNewBrush;

   // provided that we have an element named "myRect" (x:name="myRect") in
   // the generic.xaml style->Control Template-> which corresponds to that name.

}

3) Not recommended - as it belong to the scope of user-controls and not custom controls. Custom controls are the "atoms", user controls are more suitable to the purpose of combining controls.

But not impossible...

var myButton = (Button)Template.FindName("myButton",this);
myButton.OnMouseMove += ....

Just keep in mind that:

  • Anything that should be known in the code-behind must be named.

  • Your xaml should have no knowledge of what the code behind do. (except! - keep reading)

  • Parts that should be known in the code-behind must have the correct name when you design your XAML.

I truly hope this will help others who get a "wall" when trying to develop their own custom-controls.

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