如何在代码中设置绑定

本文关键字：设置 绑定 代码 | 更新日期: 2023-09-27 18:09:22

我需要在代码中设置一个绑定。

我好像做不好。

这是我尝试过的:

XAML: 

<TextBox Name="txtText"></TextBox>

背后的代码:

Binding myBinding = new Binding("SomeString");
myBinding.Source = ViewModel.SomeString;
myBinding.Mode = BindingMode.TwoWay;
myBinding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
BindingOperations.SetBinding(txtText, TextBox.TextProperty, myBinding);

ViewModel: 

public string SomeString
    {
      get
      { 
          return someString;
      }
      set 
      { 
          someString= value;
          OnPropertyChanged("SomeString");
      }
    }

设置属性时，属性没有更新。

我做错了什么?

如何在代码中设置绑定

Replace:

myBinding.Source = ViewModel.SomeString;

: 

myBinding.Source = ViewModel;

的例子:

Binding myBinding = new Binding();
myBinding.Source = ViewModel;
myBinding.Path = new PropertyPath("SomeString");
myBinding.Mode = BindingMode.TwoWay;
myBinding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
BindingOperations.SetBinding(txtText, TextBox.TextProperty, myBinding);

您的源应该只是ViewModel, .SomeString部分从Path评估(Path可以由构造函数或Path属性设置)。

您需要将source更改为viewmodel object:

myBinding.Source = viewModelObject;

除了Dyppl的答案，我认为将其放置在OnDataContextChanged事件中会很好:

private void OnDataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
{
    // Unforunately we cannot bind from the viewmodel to the code behind so easily, the dependency property is not available in XAML. (for some reason).
    // To work around this, we create the binding once we get the viewmodel through the datacontext.
    var newViewModel = e.NewValue as MyViewModel;
    var executablePathBinding = new Binding
    {
        Source = newViewModel,
        Path = new PropertyPath(nameof(newViewModel.ExecutablePath))
    };
    BindingOperations.SetBinding(LayoutRoot, ExecutablePathProperty, executablePathBinding);
}

我们也有这样的情况，我们只是保存DataContext到一个本地属性，并使用它来访问视图模型属性。选择当然是你的，我喜欢这种方法，因为它与其他方法更一致。您还可以添加一些验证，如空检查。如果你真的改变你的DataContext周围，我认为它也会很好调用:

BindingOperations.ClearBinding(myText, TextBlock.TextProperty);

清除旧视图模型的绑定(事件处理程序中的e.oldValue)。

示例:

DataContext: 

  class ViewModel
  {
    public string SomeString
    {
      get => someString;
      set 
      {
        someString = value;
        OnPropertyChanged(nameof(SomeString));
      }
    }
  }

创建绑定:

  new Binding("SomeString")
  {
    Mode = BindingMode.TwoWay,
    UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged
  };

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