这将在WPF控件中首先触发Binding触发器或Event

Question

I am forced to use a third party control for masking the text input. The XAML for the third party control looks like this
<thirdParty:MaskInput Value={Binding Path=Phone, UpdateSourceTrigger=LostFocus} x:Name=Phone LostFocus=Phone_LostFocus />

Now in my code behind I have a code for the event handler like this -
public void Phone_LostFocus(object sender, RoutedEventArgs e) { ((MaskInput)sender).Value = ((MaskInput)e.OriginalSource).Text; }

When I execute this code some times the Value property is set and some times it is not set to the text.

I suspect the Binding's UpdateSourceTrigger. Should I change it to something else? What is the order in cases like these between the UpdateSourceTrigger and event itself? Is that order predictable ie does it always happens in that order?

Answer 1

I assume you need the changes when your LostFocus event is called?

There are a few things you can do here, because as far as I know, the order is not predictable between an UpdateSourceTrigger of LostFocus and an event of LostFocus.

1.Update the source trigger at a different time. If you do it when the property changes, your model will already be updated by the time your LostFocus event is called. The drawback is that if you are doing a lot of processing behind the scenes every time the model is updated, this will run slowly.

<thirdParty:MaskInput Value={Binding Path=Phone, UpdateSourceTrigger=PropertyChanged} LostFocus=Phone_LostFocus/>

2.Propagate the changes to your model in the LostFocus event and leave your binding as OneWay (from model to control).

<thirdParty:MaskInput Value={Binding Path=Phone, Mode=OneWay}, LostFocus=Phone_LostFocus/>

public void Phone_LostFocus(object sender, RoutedEventArgs e) { 
    myPhone.Value = ((MaskInput)sender).Text;
    //rest of event code here.
}

3.Use the MaskInput value in the LostFocus event, and don't worry about when the model gets its changes.

<thirdParty:MaskInput Value={Binding Path=Phone, UpdateSourceTrigger=LostFocus}, LostFocus=Phone_LostFocus/>

public void Phone_LostFocus(object sender, RoutedEventArgs e) { 
    string currentText = ((MaskInput)sender).Text;
    //rest of event using currentText;
}