如何在代码中设置绑定？

我需要在代码中设置绑定。

我似乎不能得到它的权利。

这就是我所尝试的:

XAML:

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

暗号:

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

视图模型:

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

当我设置该属性时，它没有更新。

我做错了什么？

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最佳答案

Replace:

myBinding.Source = ViewModel.SomeString;

with:

myBinding.Source = ViewModel;

Example:

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);

Your source should be just ViewModel, the .SomeString part is evaluated from the Path (the Path can be set by the constructor or by the Path property).

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You need to change source to viewmodel object:

myBinding.Source = viewModelObject;
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In addition to the answer of Dyppl, I think it would be nice to place this inside the OnDataContextChanged event:

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);
}

We have also had cases were we just saved the DataContext to a local property and used that to access viewmodel properties. The choice is of course yours, I like this approach because it is more consistent with the rest. You can also add some validation, like null checks. If you actually change your DataContext around, I think it would be nice to also call:

BindingOperations.ClearBinding(myText, TextBlock.TextProperty);

to clear the binding of the old viewmodel (e.oldValue in the event handler).

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Example:

DataContext:

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

Create Binding:

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

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