While creating Xamarin.Forms applications, definitely you are going to need TapGestureRecognizer often. Implementing it in XAML many times may end up with a lot of unnecessary code. Let’s take a look at that simple clickable Image:
<Image Source="img.png">
<Image.GestureRecognizers>
<TapGestureRecognizer Command="{Binding CloseCommand}" CommandParamter="{Binding .}" />
</Image.GestureRecognizers>
</Image>
This is a lot of lines, especially when you have to add many clickable controls. However, we can do it better and put everything into a single line using our custom attached property:
XHTML xmlns:ex="clr-namespace:MyApp.Extensions;assembly=MyApp"
...
<Image Source="img.png" ex:Gestures.TapCommand="{ex:Command CloseCommand, Parameter={Binding .}}"/> xmlns:ex="clr-namespace:MyApp.Extensions;assembly=MyApp"
...
<Image Source="img.png" ex:Gestures.TapCommand="{ex:Command CloseCommand, Parameter={Binding .}}"/>
Implementation
using System;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
using System.Windows.Input; namespace MyApp.Extensions
{
[ContentProperty("Command")]
public class CommandExtension : BindableObject, IMarkupExtension
{
public string Command { get; set; } // Binding source for Command
public object Source { get; set; } // CommandParameter
public object Parameter { get; set; } public object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
}
}
using Xamarin.Forms;
using System.Linq; namespace MyApp.Extensions
{
public class Gestures
{
#region TapCommand public static readonly BindableProperty TapCommandProperty =
BindableProperty.CreateAttached<Gestures, CommandExtension>(
x => (CommandExtension)x.GetValue(Gestures.TapCommandProperty),
null, BindingMode.OneWay, propertyChanged: TapCommandChanged); #endregion private static void TapCommandChanged(BindableObject source, CommandExtension oldVal,
CommandExtension newVal)
{
var tapGesture = new TapGestureRecognizer(); // Set command
var commandBinding = new Binding(newVal.Command, source: newVal.Source);
tapGesture.SetBinding(TapGestureRecognizer.CommandProperty, commandBinding); // Set command parameter
if (newVal.Parameter is Binding)
{
tapGesture.SetBinding(TapGestureRecognizer.CommandParameterProperty,
newVal.Parameter as Binding);
}
else
{
tapGesture.CommandParameter = newVal.Parameter;
} // Remove old TapGestureRecognizer
var view = source as View;
var toRemove = view.GestureRecognizers.OfType<TapGestureRecognizer>().FirstOrDefault();
view.GestureRecognizers.Remove(toRemove); // Add new one
view.GestureRecognizers.Add(tapGesture);
}
}
}