Question

我有一个自定义的ContentView（FolioReceiptView），它公开了一个名为“ReceiptMarker”的属性（代码为了清晰而浓缩）：

public partial class FolioReceiptView : ContentView {
  public FolioReceiptView() {
    InitializeComponent ();
    if (!String.IsNullOrWhiteSpace (ReceiptMarker)) {
      var vm = BindingContext as FolioReceiptViewModel;
      if (vm != null) {
        vm.Marker = ReceiptMarker;
      }
    }
  }

  public static readonly BindableProperty ReceiptMarkerProperty = BindableProperty.Create ("ReceiptMarker", typeof(string), typeof(FolioReceiptView), null);

  public string ReceiptMarker { 
    get {
      return (string)GetValue (ReceiptMarkerProperty);
    } 
    set {
      SetValue (ReceiptMarkerProperty, value);
    }
  }
}

我在页面中使用控件，如下所示：

<StackLayout Orientation="Horizontal" HorizontalOptions="FillAndExpand" Spacing="10" VerticalOptions="FillAndExpand">
  <view:FolioReceiptView x:Name="ReceiptA" ReceiptMarker="A" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" />
  <view:FolioReceiptView x:Name="ReceiptB" ReceiptMarker="B" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" />
  <view:FolioReceiptView x:Name="ReceiptC" ReceiptMarker="C" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" />
</StackLayout>

但是，在类的构造函数中，ReceiptMarker值为null。为什么不从XAML中获取价值？

Answer 1

“对象初始化程序允许您在构造对象后设置属性或字段” - 这意味着在构造函数执行结束后分配ReceiptMarker =“A”。

如果希望ReceiptMarker在构造函数中可用，请将其作为参数传递。

Answer 2

事实证明，我在设置视图模型之前尝试在ViewModel上设置ReceiptMarker。现在一切都已解决。：）

处理Xamarin中自定义XAML控件的属性

2 个答案: