问题
I have a WPF TextBox that has it's text value bound in XAML. This works fine and, as expected, when the associated value is loaded to the field, it is formatted as desired.
My issue is when the user enters the text field to modify the value, I want to strip away the formatting, and display the raw underlying value.
To do this, I tried to set the BindingExpression.ParentBinding.StringFormat property, on the text boxes binding from within a GotFocus event. However, when I tried to set the StringFormat property to an empty string, I got the following exception:
Binding cannot be changed after it has been used.
So, after a control has been bound to a data model object, is there a straight-forward way that I can modify the string format of the TextBox? I'm willing to change how I format the value of the control, but the end desire is to strip the formatting of the data when it is being edited, and re-instating the string formatting once the user exits the field.
回答1:
I would probably try it differently. It sounds like you are using the same TextBox for the formatted value and editing the raw value. It would be cleaner to use two different TextBoxes for View and Edit, or package it in a UserControl. Also, I would use two properties, e.g. RawText and FormattedText, and the UserControl would have DependencyProperties with bindings to both properties. The UserControl would automatically switch to the Edit TextBox. The question of "how does the automatic switching" work may be a challenge though. You probably need to use the GotFocus of the View TextBox as you mentioned, although it might not be a bad idea to have an actual Edit button that switches it for you.
I understand about switching to WPF. There is quite a bit of adjustment (aka learning) when switching to WPF. I would think of it as designing a form or control that is "fit for purpose". You don't have to create a new UserControl though. You could do something similar to StackOverflow where there is an Edit TextBox and then the View area, that would be equivalent to the Raw and Formatted values. You would control the Visibility of the Edit TextBox through a BoolToVisibilityConverter when you are in edit mode. Create a public bool IsEditing property on your ViewModel and bind that to the <EditTextBox Visibility="{Binding IsEditing, Converter={StaticResource BoolToVisibilityConverter}}" Text="{Binding RawText}" ...etc... /> After working with WPF for a while, you really appreciate data binding and it makes it hard to go back to plain WinForms (at least for me - not to say there aren't challenges though!).
来源：https://stackoverflow.com/questions/28751867/how-can-i-change-i-e-toggle-the-bound-stringformat-property-of-a-wpf-control