WPF trigger/bindings not working

Question

I'm trying to setup a TextBox subclass that will change its style based on a few different things, and I'm running into two problems. The first Trigger, the VisualBrush one, triggers properly but won't write the text in the String myName. I tried making myName a property but for some reason the set method throws a StackOverFlowException.

The second problem is with the DataTrigger, which isn't getting triggered even though isRequired is set to false.

This is all within a custom control that inherits TextBox.

Here's my XAML:

    <TextBox.Style>
    <Style TargetType="TextBox">
        <Style.Triggers>
            <Trigger Property="Text" Value="">
                <Setter Property="Background">
                    <Setter.Value>
                        <VisualBrush Stretch="None">
                            <VisualBrush.Visual>
                                <TextBlock Foreground="Gray" FontSize="24">
                                        <TextBlock.Text>
                                            <Binding Path="myName" RelativeSource="{RelativeSource Self}" />
                                        </TextBlock.Text>
                                </TextBlock>
                            </VisualBrush.Visual>
                        </VisualBrush>
                    </Setter.Value>
                </Setter>
            </Trigger>
            <DataTrigger Binding="{Binding Path=isRequired, Source={RelativeSource Self}}" Value="False">
                <Setter Property="Text" Value="100" />
            </DataTrigger>
        </Style.Triggers>
    </Style>
</TextBox.Style>

CS:

    public partial class SuperTB : TextBox
{
    public String myName
    {
        get { return myName; }
        set {}
    }

    DependencyProperty isRequiredProperty = DependencyProperty.Register("isRequired", typeof(Boolean), typeof(SuperTB));

    public Boolean isRequired
    {
        get { return (Boolean)GetValue(isRequiredProperty); }
        set { SetValue(isRequiredProperty, value); }
    }

    public SuperTB()
    {
        InitializeComponent();
        myName = "Unicorns!";
    }

}

This is the code that StackOverflows it. Also failing to work but no Exception is:

public string myName = "Rainbows!";

Please only use the Visual Studio tag if your question actually has anything to do with it. (The fact that you wrote your code in it does on its own not entail that) — brunnerh
– brunnerh, Commented Jun 28, 2011 at 23:11

John Gardner · Accepted Answer · 2011-06-28 21:30:01Z

5

 public string myName    
 {        
     get { return myName; }        
     set {}    
 }

that property getter is returning itself, hence the stack overflow.

and the setter is doing nothing, hence the "failing to work"

you probably want:

 private string myName; // lower case!
 public string MyName    // upper case!
 {        
     get { return myName; }        
     set { myName = value; }    
 }

or even

 public string myName { get; set; }

and even then this still won't work like you expect, since nothing is firing any property change notifications there, so nobody will notice that myName ever changes.

answered Jun 28, 2011 at 21:30

John Gardner

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7 Comments

economistdolly Over a year ago

I now understand the stackoverflow. I changed it as such, and implemented INotifyPropertyChanged and fire it in the setter for myName but the binding still isn't doing anything. Here's my new code.

John Gardner Over a year ago

do you have binding errors/warnings going out to the output window? I'd check there first. I don't see anything obvious right now...

economistdolly Over a year ago

The relevant output, which I can't make sense of, is: System.Windows.Data Error: 40 : BindingExpression path error: 'myName' property not found on 'object' ''RelativeSource' (HashCode=4960368)'. BindingExpression:Path=myName; DataItem='RelativeSource' (HashCode=4960368); target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String')

Greg D Over a year ago

Your binding is on a TextBlock within the xaml. Self really means self-- if the binding lives on a TextBlock, it'll try to bind to the textblock. NOT your control. Make your source a RelativeSource with FindAncestor and look for the SuperTB type.

Greg D Over a year ago

Also note that your implementation of OnNotifyPropertyChanged doesn't follow the idiomatic practice of assigning the event to a local temporary prior to testing for null and raising. In a multi-threaded or re-entrant scenario (that you aren't even aware of), your code can explode. Instead, OnNotifyPropertyChanged should be something like this: var event = this.PropertyChanged; if (event != null) event(this, args); This eliminates a race condition that exists between testing for null and executing the delegates on the event.

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