XAML Animated Headered TextBox Style (Part 2)

Last week I wrote a blog item about the XAML Animated Headered TextBox Style. I got a lot of reactions on Twitter. Pieter Otten challenged me into adjusting my solution to make it conform the Material Design guidelines. In Android the header (Label) of the TextBox (Text Field) animates on Focus not when you enter a value. I tried to implement this by adjusting my style but that didn't work. I had to introduce an extra behavior to get it to work. See the result in this video.

MoveHeaderOnFocusBehavior

The MoveHeaderOnFocusBehavior is used to set the Visual States (Empty and NotEmpty) of the associated TextBox when it is loaded, gets the focus, loses the focus or when the text changes. This Behavior was build by subclassing the Behavior<T> class from the Microsoft.Xaml.Behaviors.Uwp.Managed NuGet package.

public class MoveHeaderOnFocusBehavior : Behavior<TextBox> {

    private bool _hasFocus;

    private void AssociatedObject_GotFocus(object sender, Windows.UI.Xaml.RoutedEventArgs e) {
        _hasFocus = true;
        UpdateState(true);
    }

    private void AssociatedObject_Loaded(object sender, RoutedEventArgs e) {
        UpdateState(false);
        this.AssociatedObject.Loaded -= this.AssociatedObject_Loaded;
    }

    private void AssociatedObject_LostFocus(object sender, Windows.UI.Xaml.RoutedEventArgs e) {
        _hasFocus = false;
        UpdateState(true);
    }

    private void AssociatedObject_TextChanged(object sender, TextChangedEventArgs e) {
        UpdateState(false);
    }

    protected override void OnAttached() {
        base.OnAttached();
        this.AssociatedObject.Loaded += this.AssociatedObject_Loaded;
        this.AssociatedObject.GotFocus += this.AssociatedObject_GotFocus;
        this.AssociatedObject.LostFocus += this.AssociatedObject_LostFocus;
        this.AssociatedObject.TextChanged += this.AssociatedObject_TextChanged;
    }

    protected override void OnDetaching() {
        base.OnDetaching();
        this.AssociatedObject.GotFocus -= this.AssociatedObject_GotFocus;
        this.AssociatedObject.LostFocus -= this.AssociatedObject_LostFocus;
        this.AssociatedObject.TextChanged -= this.AssociatedObject_TextChanged;
    }


    private void UpdateState(bool animate) {
        if (_hasFocus || !string.IsNullOrEmpty(this.AssociatedObject.Text)) {
            VisualStateManager.GoToState(this.AssociatedObject, "NotEmpty", animate);
        } else {
            VisualStateManager.GoToState(this.AssociatedObject, "Empty", animate);
        }
    }

}

Usage

I dragged and dropped the MoveHeaderOnFocusBehavior from the Assets window in Blend for Visual Studio to every TextBox of the Style 'AnimatedHeaderedTextBoxStyle'. That's all.

<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:local="using:App121"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      xmlns:Interactivity="using:Microsoft.Xaml.Interactivity"
      x:Class="App121.MainPage"
      mc:Ignorable="d">

    <StackPanel Width="300"
                Margin="0,0,60,0"
                VerticalAlignment="Top"
                HorizontalAlignment="Center">

        <TextBox Header="Firstname"
                 Style="{StaticResource AnimatedHeaderedTextBoxStyle}"
                 IsSpellCheckEnabled="False"
                 InputScope="PersonalFullName">
            <Interactivity:Interaction.Behaviors>
                <local:MoveHeaderOnFocusBehavior />
            </Interactivity:Interaction.Behaviors>
        </TextBox>

        <TextBox Header="Lastname"
                 Style="{StaticResource AnimatedHeaderedTextBoxStyle}"
                 IsSpellCheckEnabled="False"
                 Margin="0,8"
                 InputScope="PersonalFullName">
            <Interactivity:Interaction.Behaviors>
                <local:MoveHeaderOnFocusBehavior />
            </Interactivity:Interaction.Behaviors>
        </TextBox>

        <TextBox Header="E-mail"
                 x:Name="textBoxEmail"
                 Style="{StaticResource AnimatedHeaderedTextBoxStyle}"
                 IsSpellCheckEnabled="False"
                 Text="fons.sonnemans@reflectionit.nl"
                 InputScope="EmailNameOrAddress">
            <Interactivity:Interaction.Behaviors>
                <local:MoveHeaderOnFocusBehavior />
            </Interactivity:Interaction.Behaviors>
        </TextBox>

        <Button Content="Next"
                Click="Button_Click"
                Margin="0,16,0,0" />

        <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
              Height="640"
              Margin="0,0,-60,0" />
    </StackPanel>
</Page>

The code

I have published the updated code on GitHub. I hope you like it.

I also received some Twitter reactions pointing to this great Inspirational TextBox styles for Windows Phone & Store blogpost from Deani Hansen. That solution uses Styling and subclassing the TextBox control. As always there are many solutions for the same problem.

Fons

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