以编程方式从模板创建元素

Question

I'd like to move an element from one grid into another and have a problem to assign programmatically a template to the new instance. Further, details of my attempt.

For this purpose, I create an instance of the class together with its visual appearance from the template.

Inside the Window tag I declare the namespace:

xlmns:my="clr-namespace:myNameSpace"

I have a template in resources:

<ControlTemplate x:Key="templateX">
    <StackPanel>
        <Image Source="pic.png" Width="50" Height="50"/>
    </StackPanel>
</ControlTemplate>

and place the element into the grid.

<Grid Grid.Row="2">
    <StackPanel>
        <my:someClass Template="{StaticResource templateX}" MouseMove="_event">
    </StackPanel>
</Grid>

Now, I drag the element, the event "_event" fires. If I push a standard element (eg Rectangle) through this, I do the following at the end of the drag-n-drop chain of events:

Rectangle new_instance = new Rectangle();
// place for rectangle's form and color
NewPlace.Children.Add(new_instance);
// place for positioning the rectangle in NewPlace canvas

How, can I do the last part with the element of someClass? If I do

someClass new_instance = new someClass();
NewPlace.Children.Add(new_instance);

the template "templateX" isn't assigned to it.

Answer 1

The issue in this case seems to be that you want to combine two things:

• an instance of your custom class ( new_instance )
• a control template available as a XAML resource

You already know how to create the instance of your class and how to add it to the Children list.

How to retrieve the control template (or for that matter, any other object) from a XAML resource has been discussed in other SO questions, eg:

• How can I access ResourceDictionary in wpf from C# code?
• Accessing a resource via codebehind in WPF

This leads to:

ControlTemplate template = (ControlTemplate)this.FindResource("templateX");

Now, the crucial point is that you do not want to add the control template itself to the Children list. The control template is just a set of instructions how to create a UI tree for your control and bind its properties to those of your control, where appropriate.

Instead, you want to configure new_instance to use the control template you retrieved from the resource. You can do that by assigning the control template to the Template property of new_instance :

new_instance.Template = template;

Once new_instance is added to Children , it will be displayed and it will use your custom control template.