在代码隐藏中设置 Xamarin.Forms 绑定 CommandParameter
本文关键字:Forms 绑定 CommandParameter Xamarin 设置 代码 隐藏 | 更新日期: 2023-09-27 18:33:24
我正在尝试在代码中的TapGestureRecognizer
上设置绑定,但我想不出正确的方法。工作 xaml 看起来像这样...
<Grid>
<Grid.GestureRecognizers>
<TapGestureRecognizer Command="{Binding LaunchLocationDetailsCommand}"
CommandParameter="{Binding}" />
</Grid.GestureRecognizers>
</Grid>
在 C# 中,它看起来像这样...
var gridTap = new TapGestureRecognizer();
gridTap.SetBinding(TapGestureRecognizer.CommandProperty,
new Binding("LaunchLocationDetailsCommand"));
gridTap.SetBinding(TapGestureRecognizer.CommandParameterProperty,
new Binding(/* here's where I'm confused */));
var grid = new Grid();
grid.GestureRecognizers.Add(gridTap);
我的困惑在于CommandParameterProperty
的绑定.在 xaml 中,这只是{Binding}
没有其他参数。如何在代码中完成此操作?传入new Binding()
或this.BindingContext
似乎不起作用。
CommandProperty
绑定与您之前相同。
由于您没有传递到要使用的某个属性的路径,因此您的CommandParameterProperty
不能只创建一个空Binding
因为它会引发异常。
要解决此问题,您需要指定 Source
属性,正如 Adam 所指出的那样。
请注意,但是,如果您尝试分配的BindingContext
是 Null
,我怀疑这是在您的情况下,这仍然会引发异常。
以下示例中的Grid
将BindingContext
设置为视图模型 ( objGrid.BindingContext = objMyView2
(。
然后,我们为命令参数创建一个新的绑定,Source
指向我们的视图模型 ( Source = objGrid.BindingContext
(。
如果运行下面的演示,您将在Output
窗口中看到一条调试消息,指示视图模型中的属性值。
MyView2 objMyView2 = new MyView2();
objMyView2.SomeProperty1 = "value1";
objMyView2.SomeProperty2 = "value2";
objMyView2.LaunchLocationDetailsCommand_WithParameters = new Command<object>((o2)=>
{
LaunchingCommands.LaunchLocationDetailsCommand_WithParameters(o2);
});
Grid objGrid = new Grid();
objGrid.BindingContext = objMyView2;
objGrid.HeightRequest = 200;
objGrid.BackgroundColor = Color.Red;
TapGestureRecognizer objTapGestureRecognizer = new TapGestureRecognizer();
objTapGestureRecognizer.SetBinding(TapGestureRecognizer.CommandProperty, new Binding("LaunchLocationDetailsCommand_WithParameters"));
Binding objBinding1 = new Binding()
{
Source = objGrid.BindingContext
};
objTapGestureRecognizer.SetBinding(TapGestureRecognizer.CommandParameterProperty, objBinding1);
//
objGrid.GestureRecognizers.Add(objTapGestureRecognizer);
支持课程:-
我的视图2:-
public class MyView2
: ViewModelBase
{
public string SomeProperty1 { get; set; }
public string SomeProperty2 { get; set; }
public ICommand LaunchLocationDetailsCommand_WithParameters { get; set; }
}
启动命令:-
public static class LaunchingCommands
{
public static void LaunchLocationDetailsCommand_WithParameters(object pobjObject)
{
System.Diagnostics.Debug.WriteLine("SomeProperty1 = " + (pobjObject as MyView2).SomeProperty1);
}
}
视图模型库:-
public abstract class ViewModelBase
: INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void RaisePropertyChanged(string pstrPropertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(pstrPropertyName));
}
}
}
如果你有一个 {Binding},里面没有任何内容,它就会绑定到绑定上下文并将其传递。因此,将其绑定到页面的默认绑定上下文。
创建新的绑定时,设置源。
var binding = new Xamarin.Forms.Binding() { Source = this.BindingContext };