我想通过创建新的可绑定(bind)属性将 CustomLabel 绑定(bind)到虚拟机。
在 OneWay 模式下,第一个 VM 数据已正确更改 CustomLabel 的属性。但从第二次开始就不行了。
尽管发生了 VM 事件,但 CustomView 的 Bindable 属性尚未触发其 PropertyChanged 事件。
不过它在 TwoWay 模式下工作正常。
我测试了两天,寻找原因,但没找到很好的办法。
有人告诉我该怎么做吗?
// HomeViewModel.cs
public class HomeViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string _customName = "-";
public string CustomName
{
get
{
Debug.WriteLine("Get_CustomName");
return _customName;
}
set
{
if (value != _customName)
{
Debug.WriteLine("Set_CustomName");
_customName = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(CustomName)));
}
}
}
}
// MainPage.cs
public partial class MainPage : ContentPage
{
HomeViewModel Vm = new HomeViewModel();
public MainPage()
{
InitializeComponent();
BindingContext = Vm;
}
void ButtonTrue_Clicked(object sender, EventArgs e)
{
Vm.CustomName = "True";
}
void ButtonFalse_Clicked(object sender, EventArgs e)
{
Vm.CustomName = "False";
}
}
<!-- MainPage.xaml -->
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:Ex_Binding"
xmlns:d="http://xamarin.com/schemas/2014/forms/design"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
x:Class="Ex_Binding.MainPage">
<StackLayout Padding="50,0" VerticalOptions="Center">
<StackLayout Orientation="Horizontal" HorizontalOptions="Center">
<Label Text="Custom Result : " />
<local:CustomLabel x:Name="lbCustom" MyText="{Binding CustomName}" HorizontalOptions="Center" />
</StackLayout>
<StackLayout Orientation="Horizontal">
<Button Text="TRUE" BackgroundColor="LightBlue" HorizontalOptions="FillAndExpand" Clicked="ButtonTrue_Clicked" />
<Button Text="FALSE" BackgroundColor="LightPink" HorizontalOptions="FillAndExpand" Clicked="ButtonFalse_Clicked" />
</StackLayout>
</StackLayout>
</ContentPage>
// CustomLabel.cs
public class CustomLabel : Label
{
public static readonly BindableProperty MyTextProperty = BindableProperty.Create(nameof(MyText), typeof(string), typeof(CustomLabel), null, BindingMode.OneWay, propertyChanged: OnMyTextChanged);
private static void OnMyTextChanged(BindableObject bindable, object oldValue, object newValue)
{
var thisBindable = (CustomLabel)bindable;
if (thisBindable != null)
{
thisBindable.MyText = (string)newValue;
}
}
public string MyText
{
get => (string)GetValue(MyTextProperty);
set
{
SetValue(MyTextProperty, value);
Text = value;
}
}
}
最佳答案
原因:
thisBindable.MyText = (string)newValue;
因为当MyText的值改变时你设置了它的值。所以下次它永远不会被调用(在 TwoWay 中该方法将被调用多次)。
解决方案:
您应该直接在OnMyTextChanged
中设置Text。
private static void OnMyTextChanged(BindableObject bindable, object oldValue, object newValue)
{
var thisBindable = (CustomLabel)bindable;
if (thisBindable != null)
{
thisBindable.Text = (string)newValue;
}
}
public string MyText
{
get => (string)GetValue(MyTextProperty);
set
{
SetValue(MyTextProperty, value);
//Text = value;
}
}
关于Xamarin Forms 可绑定(bind)属性与 OneWay 不起作用,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/59873353/