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:
1 <Image Source=
"img.png">
2 <Image.GestureRecognizers>
3 <TapGestureRecognizer Command=
"{Binding CloseCommand}" CommandParamter=
"{Binding .}" />
4 </Image.GestureRecognizers>
5 </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
1 using System;
2 using Xamarin.Forms;
3 using Xamarin.Forms.Xaml;
4 using System.Windows.Input;
5
6 namespace MyApp.Extensions
7 {
8 [ContentProperty(
"Command")]
9 public class CommandExtension : BindableObject, IMarkupExtension
10 {
11 public string Command {
get;
set; }
12
13 // Binding source for Command
14 public object Source {
get;
set; }
15
16 // CommandParameter
17 public object Parameter {
get;
set; }
18
19 public object ProvideValue(IServiceProvider serviceProvider)
20 {
21 return this;
22 }
23 }
24 }
1 using Xamarin.Forms;
2 using System.Linq;
3
4 namespace MyApp.Extensions
5 {
6 public class Gestures
7 {
8 #region TapCommand
9
10 public static readonly BindableProperty TapCommandProperty =
11 BindableProperty.CreateAttached<Gestures, CommandExtension>
(
12 x =>
(CommandExtension)x.GetValue(Gestures.TapCommandProperty),
13 null, BindingMode.OneWay, propertyChanged: TapCommandChanged);
14
15 #endregion
16
17 private static void TapCommandChanged(BindableObject source, CommandExtension oldVal,
18 CommandExtension newVal)
19 {
20 var tapGesture =
new TapGestureRecognizer();
21
22 // Set command
23 var commandBinding =
new Binding(newVal.Command, source: newVal.Source);
24 tapGesture.SetBinding(TapGestureRecognizer.CommandProperty, commandBinding);
25
26 // Set command parameter
27 if (newVal.Parameter
is Binding)
28 {
29 tapGesture.SetBinding(TapGestureRecognizer.CommandParameterProperty,
30 newVal.Parameter
as Binding);
31 }
32 else
33 {
34 tapGesture.CommandParameter =
newVal.Parameter;
35 }
36
37 // Remove old TapGestureRecognizer
38 var view = source
as View;
39 var toRemove = view.GestureRecognizers.OfType<TapGestureRecognizer>
().FirstOrDefault();
40 view.GestureRecognizers.Remove(toRemove);
41
42 // Add new one
43 view.GestureRecognizers.Add(tapGesture);
44 }
45 }
46 }
转载于:https://www.cnblogs.com/mschen/p/10565231.html
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