xamarin.forms - Flexlayout 不适用于命令和命令参数
问题描述
我正在尝试使用 flexlayout,它很棒,但现在对于堆栈布局中的每个项目,我需要添加轻按手势、命令等。
无论我尝试什么都不起作用。唯一有效的是stacklayout.TapGestureRecognizer,但是一旦我尝试使用该命令就不起作用。
我什至尝试了https://taubensee.net/adding-touch-events-to-flexlayouts/ 并添加了一个命令参数可绑定属性,但也不起作用。
如何将带有命令参数的命令添加到 flexlayout 。下面是我的代码
<FlexLayout BindableLayout.ItemsSource="{Binding Customers}"
AlignContent="Start"
AlignItems="Start"
Direction="Row"
JustifyContent="Start"
Wrap="Wrap">
<BindableLayout.ItemTemplate>
<DataTemplate>
<StackLayout
FlexLayout.AlignSelf="Start"
FlexLayout.Basis="50%">
<!--<StackLayout.GestureRecognizers>
<TapGestureRecognizer Tapped="TapGestureRecognizer_Tapped" />
</StackLayout.GestureRecognizers>-->
<Frame>
<!--<Frame.GestureRecognizers>
<TapGestureRecognizer
Command="{Binding ItemTappedCommand}"
CommandParameter="{Binding .}" />
</Frame.GestureRecognizers>-->
<StackLayout>
<Label Text="whatever"></Label>
<!--<Image Source="myimage.png">
<Image.GestureRecognizers>
<TapGestureRecognizer Command="{Binding ItemTappedCommand}" CommandParameter="AAAA"
NumberOfTapsRequired="1"></TapGestureRecognizer>
</Image.GestureRecognizers>
</Image>-->
</StackLayout>
</Frame>
</StackLayout>
</DataTemplate>
</BindableLayout.ItemTemplate>
<!--<FlexLayout.Behaviors>
<behaviors:FlexLayoutItemTappedBehavior
Command="{Binding ItemTappedCommand2}" CommandParameter="{Binding .}"/>
</FlexLayout.Behaviors>-->
</FlexLayout>
解决方案
FlexLayout可能会错过触摸事件和命令,请尝试使用Behavior来实现。
创建一个继承自的新类Behavior<T>
:
public class FlexLayoutItemTappedBehavior : Behavior<FlexLayout>
{
public static readonly BindableProperty CommandProperty =
BindableProperty.Create(nameof(Command), typeof(ICommand), typeof(FlexLayoutItemTappedBehavior), defaultBindingMode: BindingMode.OneWay);
public static readonly BindableProperty ParamaterProperty =
BindableProperty.Create(nameof(Paramater), typeof(object), typeof(FlexLayoutItemTappedBehavior), defaultBindingMode: BindingMode.OneWay);
public ICommand Command
{
get => (ICommand)this.GetValue(CommandProperty);
set => this.SetValue(CommandProperty, value);
}
public object Paramater
{
get => (object)this.GetValue(ParamaterProperty);
set => this.SetValue(ParamaterProperty, value);
}
protected override void OnAttachedTo(FlexLayout bindable)
{
base.OnAttachedTo(bindable);
if (bindable.BindingContext != null)
{
this.BindingContext = bindable.BindingContext;
}
bindable.BindingContextChanged += this.OnFlexLayoutBindingChanged;
bindable.ChildAdded += this.OnFlexLayoutChildAdded;
}
protected override void OnDetachingFrom(FlexLayout bindable)
{
base.OnDetachingFrom(bindable);
bindable.BindingContextChanged -= this.OnFlexLayoutBindingChanged;
bindable.ChildAdded -= this.OnFlexLayoutChildAdded;
foreach (var child in bindable.Children)
{
if (child is View childView && childView.GestureRecognizers.Any())
{
var tappedGestureRecognizers = childView.GestureRecognizers.Where(x => x is TapGestureRecognizer).Cast<TapGestureRecognizer>();
foreach (var tapGestureRecognizer in tappedGestureRecognizers)
{
tapGestureRecognizer.Tapped -= this.OnItemTapped;
childView.GestureRecognizers.Remove(tapGestureRecognizer);
}
}
}
}
private void OnFlexLayoutBindingChanged(object sender, EventArgs e)
{
if (sender is FlexLayout flexLayout)
{
this.BindingContext = flexLayout.BindingContext;
}
}
private void OnFlexLayoutChildAdded(object sender, ElementEventArgs args)
{
if (args.Element is View view)
{
var tappedGestureRecognizer = new TapGestureRecognizer();
tappedGestureRecognizer.Tapped += this.OnItemTapped;
view.GestureRecognizers.Add(tappedGestureRecognizer);
}
}
private async void OnItemTapped(object sender, EventArgs e)
{
if (sender is VisualElement visualElement)
{
var animations = new List<AnimationBase>();
var scaleIn = new ScaleToAnimation
{
Target = visualElement,
Scale = .95,
Duration = "50"
};
animations.Add(scaleIn);
var scaleOut = new ScaleToAnimation
{
Target = visualElement,
Scale = 1,
Duration = "50"
};
animations.Add(scaleOut);
var storyBoard = new StoryBoard(animations);
await storyBoard.Begin();
}
if (sender is BindableObject bindable && this.Command != null && this.Command.CanExecute(null))
{
object resolvedParameter;
if (Paramater != null)
{
resolvedParameter = Paramater;
}
else
{
resolvedParameter = e;
}
if (Command.CanExecute(resolvedParameter))
{
this.Command.Execute(bindable.BindingContext);
}
}
}
}
最后,为了使用Behavior
from XAML
,您可以像这样引用它:
<FlexLayout.Behaviors>
<behaviors:FlexLayoutItemTappedBehavior
Command="{Binding NavigateToDetailCommand}" Paramater="{Binding .}"/>
</FlexLayout.Behaviors>
关于可重用的EventToCommandBehavior,可以参考这里。