Csharp 无法通过绑定禁用条目

发布于02月24日

在我的Maui XAML中，我有一个最初启用的Entry控件，一旦用户在该控件中输入了正确的值，我希望以编程方式禁用它.

但事实并非如此

我的xaml代码看起来像这样

 <Entry
     x:Name="InputAnswer"
     Margin="0,0,20,0"
     FontSize="24"
     HorizontalOptions="Start"
     IsEnabled="{Binding IsWrong}"
     Keyboard="Numeric"
     MaxLength="5"
     Placeholder=""
     Text="{Binding InputAnswer}" />

我的模特班

  public class EquationWithInput: Equation, INotifyPropertyChanged
  {
      public int? InputAnswer {  get; set; }
      public int CorrectAnswer{  get; set; }
      public bool IsWrong { get => InputAnswer == null ? true : InputAnswer != CorrectAnswer; }
      ...
  }

但当我判断结果时，该控件从未被禁用.绑定似乎不起作用，但对于所有其他属性，它在此页面中的其他所有位置都有效.例如，InputAnswer人.

那么我需要做些什么才能让这件事起作用呢？

推荐答案

您需要确保EquationWithInput类正确实现INotifyPropertyChanged接口，并在InputAnswer更改时引发PropertyChanged事件，因为这会间接影响IsWrong属性.

以下是如何修改EquationWithInput类，以确保对InputAnswer的更改也正确地通知UI有关IsWrong属性的更新:

public class EquationWithInput : Equation, INotifyPropertyChanged
{
    private int? inputAnswer;
    public int? InputAnswer
    {
        get { return inputAnswer; }
        set
        {
            if (inputAnswer != value)
            {
                inputAnswer = value;
                OnPropertyChanged(nameof(InputAnswer));
                // Since IsWrong depends on InputAnswer, it needs to notify the change as well.
                OnPropertyChanged(nameof(IsWrong));
            }
        }
    }

    public int CorrectAnswer { get; set; }

    public bool IsWrong => InputAnswer == null || InputAnswer != CorrectAnswer;

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

}