Question

I have a textbox containing a decimal value on my interface that I want to clear whenever the user selects it.

However, if the user doesn’t make any changes and selects another interface element I need the text to revert to whatever it was previous to the clear.

So far I have the the following style:

<Style x:Key="CustomTextBoxStyle" TargetType="{x:Type TextBox}">
     <Setter Property="Text" Value="{Binding RelativeSource={RelativeSource Self}, Path=Tag}"/>
        <Style.Triggers>
            <Trigger Property="IsFocused" Value="True">
                <Setter Property="Text" Value="{x:Null}" />
            </Trigger>
        </Style.Triggers>
    </Style>

And then the following to use the style:

<TextBox Style="{DynamicResource CustomTextBoxStyle}" 
                     Tag="{Binding myDecimalValue, StringFormat=#.###}" 
                     TabIndex="1" />

However, in this scenario the value reverts back to what it was even when the user enters a new value.

Can anyone tell me the best way to go about achieving this?

Thanks,

Answer 1

Thanks for the help, but I was able to achieve what I was looking for and adhere to MVVM principles by using the AttachedProperty described at the following:

https://stackoverflow.com/a/7972361/1466960

This allowed me to bind the IsFocused property to a value in my view model and proceed in a similar fashion to the one described by Ryan Amies.

View Model:

bool isFocused = false;
double original;

public bool IsFocused
{
    get
    {
        return isFocused;
    }
    set
    {
        isFocused = value;

        if (isFocused)
        {
            original = current;
            current = "";
        }
        else
        {
            if (HundredPercentLine == "")
                current = original;
        }

        OnPropertyChanged(new PropertyChangedEventArgs("IsFocused"));
    }
}