How to create event for subclassed control

Lloyd Sheen 1,476

I use GestureRecognizers with Label in lots of places in an app and would like to create a new Label control that basically uses Label as the base and adds a TapGestureRecognizer that invokes an event that can be defined in XAML.

I know how to subclass the Label control and add the GestureReconizer/TapGestureRecongizer in C# but not how to create the event that a user can provide to handle the Tap.

Lloyd Sheen 1,476

The C# code I have for the sub classed control is:

using Maui.BindableProperty.Generator.Core;

namespace SubClassControls

{

public partial  class SubLabel : Label

{

    public  SubLabel() 

    {

        TapGestureRecognizer tapGestureRecognizer = new TapGestureRecognizer();

        tapGestureRecognizer.Tapped += (s, e) =>

        {

            // Handle the tap

            DoSomeThingOnTap();

        };

        this.GestureRecognizers.Add(tapGestureRecognizer);

        this.TextDecorations = TextDecorations.Underline;

    }

    private void DoSomeThingOnTap()

    {

        BackgroundColor = Colors.Red;

    }

    [AutoBindable(OnChanged = nameof(UpdateIsUnderlined), DefaultValue = "true")]

    private readonly bool _isUnderlined;

    private void UpdateIsUnderlined(bool value)

    {

        if (value==false) 

        {

            this.TextDecorations = TextDecorations.None;

        }

    }

}

}

What I need is code that will call whatever routine is defined in the XAML for the Tapped event. I need a way of defining it so it can be used in XAML and the actual call when the Tap occurs (the code for DoSomethingOnTap)

Leon Lu (Shanghai Wicresoft Co,.Ltd.) 71,931 Microsoft Vendor

How to create event for subclassed control

First, create a public event and handler in your SubLabel class:

public delegate void SubLabelSelectedHandler(object sender, EventArgs e);
public event SubLabelSelectedHandler OnLabelSelected;

Then, inside the tapGestureRecognizer.Tapped of control, you can call the handler if it exists

  tapGestureRecognizer.Tapped += (s, e) =>
  {
            // Handle the tap
            // check if a handler is assigned
            if (OnLabelSelected != null)
            {
                OnLabelSelected(this, new EventArgs());
            }
 
            DoSomeThingOnTap();
 
   };

When you use this SubLabel, you can invoke this event in the XAML.

            <local:SubLabel Text="123456" OnLabelSelected="SubLabel_OnLabelSelected"></local:SubLabel>

And implement this event in the layout background code.

private void SubLabel_OnLabelSelected(object sender, EventArgs e)
{
     DisplayAlert("InFo", "SubLabel_OnLabelSelected Executed", "OK");
}

1 answer

Lloyd Sheen 1,476 Reputation points

2024-05-29T12:50:56.2366667+00:00

I actually found something simpler.

It works and not sure if it might have problems but all I needed to do is the following:

In the control code I added:

public event EventHandler Tapped;

and in the DoSomeThingOnTap I added:

// the ? means that if the Tapped is not set then don't executed it

Tapped?.Invoke(this, null);
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Leon Lu (Shanghai Wicresoft Co,.Ltd.) 71,931 Reputation points Microsoft Vendor

2024-05-30T03:31:27.8+00:00

Thanks for your update and sharing.
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How to create event for subclassed control

1 answer