Silverlight 4 TextBox Update Source on Text Changed Behavior

Here is a simple little behavior for updating a TextBox's Text property in Silverlight when the text changes instead of when it loses focus.

Quick and Easy.  Gotta Love Behaviors.

Jacob

Silverlight Fade Control Behavior - FadeyBehavior

In my last post about Silverlight Property Triggers and Storyboard Actions I showed a way for us to fade in an element when a property on our view model was a certain value.  We used this to fade in a list of items after we loaded them, and ultimately we could fade them out while we were re-loading more items.  The code looked kind of like this;

<ItemsControl
    Margin="0 130 0 0"
    HorizontalAlignment="Left"
    VerticalAlignment="Top"
    Opacity="0.0"
    ItemsSource="{Binding Items}">
            <i:Interaction.Triggers>
                <local:BooleanPropertyTrigger
                    Binding="{Binding FinishedLoading}"
                    TriggerValue="True">
                    <local:StoryboardAction>
                        <Storyboard>
                            <DoubleAnimation
                                To="1.0"
                                Duration="00:00:0.7"
                                Storyboard.TargetProperty="Opacity" />
                        </Storyboard>
                    </local:StoryboardAction>
                </local:BooleanPropertyTrigger>
                <local:BooleanPropertyTrigger
                    Binding="{Binding FinishedLoading}"
                    TriggerValue="False">
                    <local:StoryboardAction>
                        <Storyboard>
                            <DoubleAnimation
                                To="0.0"
                                Duration="00:00:0.4"
                                Storyboard.TargetProperty="Opacity" />
                        </Storyboard>
                    </local:StoryboardAction>
                </local:BooleanPropertyTrigger>
            </i:Interaction.Triggers>
                <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Border
                Height="30"
                Width="200"
                Margin="0 2"
                BorderBrush="Plum"
                BorderThickness="3"
                CornerRadius="5">
                <TextBlock
                    VerticalAlignment="Center"
                    HorizontalAlignment="Left"
                    Margin="5 0 0 0"
                    Text="{Binding Name}" />
            </Border>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

Now, the more I looked at all that XAML the more I thought we could make this a lot simpler.  By the end of this post we will hopefully end up having something much simpler to use; like this;

<ItemsControl
    Margin="0 130 0 0"
    HorizontalAlignment="Left"
    VerticalAlignment="Top"
    Opacity="0.0"
    ItemsSource="{Binding Items}">
    <i:Interaction.Behaviors>
        <local:FadeyBehavior
            Binding="{Binding FinishedLoading}" />
    </i:Interaction.Behaviors>
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Border
                Height="30"
                Width="200"
                Margin="0 2"
                BorderBrush="Plum"
                BorderThickness="3"
                CornerRadius="5">
                <TextBlock
                    VerticalAlignment="Center"
                    HorizontalAlignment="Left"
                    Margin="5 0 0 0"
                    Text="{Binding Name}" />
            </Border>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

So, what we've done is encompassed our two triggers and their storyboards into a new Behavior.  Our new FadeyBehavior creates and attaches our to FadeIn and FadeOut triggers along with the associated FadeInAction and FadeOutAction.  The secret sauce is in cascading the binding down to the triggers in the code behind.

using System.Windows;
using System.Windows.Data;
using System.Windows.Interactivity;

/// <summary>
/// A behavior for fading an element based on whether a bound property is true or false.
/// </summary>
public class FadeyBehavior : Behavior<FrameworkElement>
{
    /// <summary>
    /// The <see cref="Binding" /> dependency property's name.
    /// </summary>
    public const string BindingPropertyName = "Binding";

    /// <summary>
    /// Gets or sets the value of the <see cref="Binding" />
    /// property. This is a dependency property.
    /// </summary>
    public object Binding
    {
        get
        {
            return (object)GetValue(BindingProperty);
        }
        set
        {
            SetValue(BindingProperty, value);
        }
    }

    /// <summary>
    /// Identifies the <see cref="Binding" /> dependency property.
    /// </summary>
    public static readonly DependencyProperty BindingProperty = DependencyProperty.Register(
        BindingPropertyName,
        typeof(object),
        typeof(FadeyBehavior),
        new PropertyMetadata(null));


    protected override void OnAttached()
    {
        if (AssociatedObject.Opacity != 0.0)
            AssociatedObject.Opacity = 0.0;

        // Create our fade in/out triggers
        var triggerIn = new FadeInTrigger();
        var triggerOut = new FadeOutTrigger();

        // Bind the Binding property in this behavior to the underlying triggers.
        var b = new Binding("Binding") { Source = this };
        BindingOperations.SetBinding(triggerIn, BooleanPropertyTrigger.BindingProperty, b);
        BindingOperations.SetBinding(triggerOut, BooleanPropertyTrigger.BindingProperty, b);

        // Add our triggers to the associated object.
        var currTriggers = Interaction.GetTriggers(AssociatedObject);
        currTriggers.Add(triggerIn);
        currTriggers.Add(triggerOut);

        base.OnAttached();
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
    }
}

For the time being, I've only had to use this for a boolean property trigger, but it could be expanded into a base class for other trigger types (String, DateTime range, WidgetA, etc.).

You can download the code to mess around with it yourself.

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Silverlight Storyboard and FadeIn FadeOut Actions

In my last post I talked about Silverlight Property Triggers and how we could use them to trigger functionality when a property on our ViewModel was a certain value.  The keen observer will have noted that I glossed over a bit of magic that was happening in the StoryboardAction.  Today's post is going to cover how to create your very own StoryboardAction to love and cherish for all time.  Here is a quick re-cap of what our XAML looked like in the last post;

<ItemsControl
    Margin="0 130 0 0"
    HorizontalAlignment="Left"
    VerticalAlignment="Top"
    Opacity="0.0"
    ItemsSource="{Binding Items}">
            <i:Interaction.Triggers>
                <local:BooleanPropertyTrigger
                    Binding="{Binding FinishedLoading}"
                    TriggerValue="True">
                    <local:StoryboardAction>
                        <Storyboard>
                            <DoubleAnimation
                                To="1.0"
                                Duration="00:00:0.7"
                                Storyboard.TargetProperty="Opacity" />
                        </Storyboard>
                    </local:StoryboardAction>
                </local:BooleanPropertyTrigger>
                <local:BooleanPropertyTrigger
                    Binding="{Binding FinishedLoading}"
                    TriggerValue="False">
                    <local:StoryboardAction>
                        <Storyboard>
                            <DoubleAnimation
                                To="0.0"
                                Duration="00:00:0.4"
                                Storyboard.TargetProperty="Opacity" />
                        </Storyboard>
                    </local:StoryboardAction>
                </local:BooleanPropertyTrigger>
            </i:Interaction.Triggers>
                <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Border
                Height="30"
                Width="200"
                Margin="0 2"
                BorderBrush="Plum"
                BorderThickness="3"
                CornerRadius="5">
                <TextBlock
                    VerticalAlignment="Center"
                    HorizontalAlignment="Left"
                    Margin="5 0 0 0"
                    Text="{Binding Name}" />
            </Border>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

Today, we added another trigger to fade the items out when we re-load our items.  Then, we are going to encapsulate the fade animations in a new action that will reduce our XAML a little bit.

First, lets take a quick look at the StoryboardAction Source.

using System;
using System.Windows;
using System.Windows.Interactivity;
using System.Windows.Markup;
using System.Windows.Media.Animation;

[ContentProperty("Story")]
public class StoryboardAction : TriggerAction<FrameworkElement>
{
    /// <summary>
    /// Holder for a target setting state.
    /// </summary>
    private bool hasTargetSet = false;

    /// <summary>
    /// Gets or sets the storyboard for this action.
    /// </summary>
    /// <value>The storyboard to run when invoked.</value>
    public Storyboard Story { get; set; }

    /// <summary>
    /// The <see cref="Target" /> dependency property's name.
    /// </summary>
    public const string TargetPropertyName = "Target";

    /// <summary>
    /// Gets or sets the value of the <see cref="Target" />
    /// property. This is a dependency property. 
    /// You can leave this un-set if you want to use the Trigger's 
    /// AssociatedObject as the Target.
    /// </summary>
    public DependencyObject Target
    {
        get
        {
            return (DependencyObject)GetValue(TargetProperty);
        }
        set
        {
            SetValue(TargetProperty, value);
        }
    }

    /// <summary>
    /// Identifies the <see cref="Target" /> dependency property.
    /// </summary>
    public static readonly DependencyProperty TargetProperty = DependencyProperty.Register(
        TargetPropertyName,
        typeof(DependencyObject),
        typeof(StoryboardAction),
        new PropertyMetadata(null));
        

    /// <summary>
    /// Invokes the action.
    /// </summary>
    /// <param name="parameter">The parameter to the action. If the action does not require a parameter, the parameter may be set to a null reference.</param>
    protected override void Invoke(object parameter)
    {
        if (this.Story == null)
            return;

        if(!hasTargetSet)
        {
            // Fall back to the associated object if no target defined.
            var target = this.Target ?? AssociatedObject;
            if (target != null)
            {
                Storyboard.SetTarget(this.Story, target);
                hasTargetSet = true;
            }
        }

        // Stop any previously ran storyboards.
        if (this.Story.GetCurrentState() != ClockState.Stopped)
            this.Story.Stop();
            
        this.Story.Begin();            
    }
}

The important parts of this class are the Invoke logic.  We are doing some basic null checking, then setting the target for our animation to either the Target or the AssociatedObject if no Target was found.  Finally, we make sure the animation is not currently running, then start up our animation.

Extra Snazzy Bonus Implementation Codez


I feel like we are really connecting here, so I'm gonna throw in some extra snazzy bonus material just for you.  Here are some short hand versions of our Opacity Fade Animations that should tame the XAML Monster.

using System;
using System.Windows;
using System.Windows.Media.Animation;

public class FadeOutAction : FadeAction
{
    public FadeOutAction()
        : base(.2, 0.0)
    { }
}

public class FadeInAction : FadeAction
{
    public FadeInAction()
        : base(.6, 1.0)
    { }
}

public class FadeAction : StoryboardAction
{

    public FadeAction(double durationSeconds = .6, double fadeTo = 0.0)
    {
        var anim = new DoubleAnimation { Duration = new Duration(TimeSpan.FromSeconds(durationSeconds)), To = fadeTo };
        Storyboard.SetTargetProperty(anim, new PropertyPath("Opacity"));

        this.Story = new Storyboard();
        this.Story.Children.Add(anim);
    }
}

Now our XAML is looking slightly better.

<ItemsControl
    Margin="0 130 0 0"
    HorizontalAlignment="Left"
    VerticalAlignment="Top"
    Opacity="0.0"
    ItemsSource="{Binding Items}">
            <i:Interaction.Triggers>
                <local:BooleanPropertyTrigger
                    Binding="{Binding FinishedLoading}"
                    TriggerValue="True">
                    <local:FadeInAction />
                </local:BooleanPropertyTrigger>
                <local:BooleanPropertyTrigger
                    Binding="{Binding FinishedLoading}"
                    TriggerValue="False">
                    <local:FadeOutAction />
                </local:BooleanPropertyTrigger>
            </i:Interaction.Triggers>
                <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Border
                Height="30"
                Width="200"
                Margin="0 2"
                BorderBrush="Plum"
                BorderThickness="3"
                CornerRadius="5">
                <TextBlock
                    VerticalAlignment="Center"
                    HorizontalAlignment="Left"
                    Margin="5 0 0 0"
                    Text="{Binding Name}" />
            </Border>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

Next time, we will create a new FadeyBehavior to encapsulate our fading triggers.

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Silverlight 4 Property Triggers

I spent a little time this week messing around with the newly added Triggers and TriggerActions available through the new Expression Blend 4 SDK.

Triggers and Behaviors are really just ways to attach functionality to an existing element, and the base classes that are included in the newer version of Silverlight 4 really make the job easier.  I'm going to walk through adding a trigger that fires when one of the properties on my ViewModel changes to true.  Now allegedly there is an existing trigger (DataStoreChangedTrigger) that will fire actions based on when a bound property changes, but I want to only fire my actions when my bound property becomes a specific value.

Our Goal

<ItemsControl
    Margin="0 130 0 0"
    HorizontalAlignment="Left"
    VerticalAlignment="Top"
    Opacity="0.0"
    ItemsSource="{Binding Items}">
    <i:Interaction.Triggers>
        <local:BooleanPropertyTrigger
            Binding="{Binding FinishedLoading}"
            TriggerValue="True">
            <local:StoryboardAction>
                <Storyboard>
                    <DoubleAnimation
                        To="1.0"
                        Duration="00:00:0.7"
                        Storyboard.TargetProperty="Opacity" />
                </Storyboard>
            </local:StoryboardAction>
        </local:BooleanPropertyTrigger>
    </i:Interaction.Triggers>
</ItemsControl>

The Codez

[Download the PropertyTrigger Example Source Project and play along at home]

To start out with, I create a base PropertyChangedTrigger class that will do most of the heavy lifting for us.  Essentially, we want to inherit from the TriggerBase<...> generic base class and specify that we want our Trigger to attach to a FrameworkElement (I suppose you could use another type of control class, but FrameworkElement will encompass just about any element with a DataContext, which I find useful).  Our PropertyChangedTrigger will expose a Binding property that will allow us to attach an event handler when our bound property changes so we can invoke our TriggerActions.

/// <summary>
/// A base property changed trigger that
/// fires whenever the bound property changes.
/// </summary>
public class PropertyChangedTrigger : TriggerBase<FrameworkElement>
{
    /// <summary>
    /// The <see cref="Binding" /> dependency property's name.
    /// </summary>
    public const string BindingPropertyName = "Binding";

    /// <summary>
    /// Gets or sets the value of the <see cref="Binding" />
    /// property. This is a dependency property.
    /// </summary>
    public object Binding
    {
        get
        {
            return (object)GetValue(BindingProperty);
        }
        set
        {
            SetValue(BindingProperty, value);
        }
    }

    /// <summary>
    /// Identifies the <see cref="Binding" /> dependency property.
    /// </summary>
    public static readonly DependencyProperty BindingProperty =
        DependencyProperty.Register(
        BindingPropertyName,
        typeof(object),
        typeof(PropertyChangedTrigger),
        new PropertyMetadata(null,
            new PropertyChangedCallback(Binding_ValueChanged)));

    /// <summary>
    /// Called after the trigger is attached to an AssociatedObject.
    /// </summary>
    protected override void OnAttached()
    {
        base.OnAttached();
    }

    /// <summary>
    /// Called when the trigger is being detached
    /// from its AssociatedObject,
    /// but before it has actually occurred.
    /// </summary>
    protected override void OnDetaching()
    {
        base.OnDetaching();
    }

    /// <summary>
    /// Occurs when Binding's value changes.
    /// </summary>
    /// <param name="obj">The obj on which the binding changed.</param>
    /// <param name="args">The <see cref="System.Windows.DependencyPropertyChangedEventArgs"/> instance containing the event data.</param>
    private static void Binding_ValueChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
    {
        var trig = obj as PropertyChangedTrigger;
        if (trig != null && trig.ShouldTriggerFire(args.NewValue))
        {
            trig.OnPropertyTrigger(args.NewValue);
        }
    }

    /// <summary>
    /// Does the change logic test. By default, it will always fire on value change.
    /// </summary>
    /// <param name="newValue">The new value.</param>
    /// <returns>True if the trigger should fire, otherwise false.</returns>
    protected virtual bool ShouldTriggerFire(object newValue)
    {
        return true;
    }

    /// <summary>
    /// Called when [property trigger].
    /// </summary>
    /// <param name="value">The value of the property.</param>
    protected virtual void OnPropertyTrigger(object value)
    {
        base.InvokeActions(value);
    }
}

As you can tell, our PropertyChangedTrigger makes use of a virtual method ShouldTriggerFire(…) that will default to just fire everytime a property changes value. Next, we will override our base class to create an EqualsPropertyTrigger that only fires when the value changes to a specific one that we want.

/// <summary>
/// A base class for property triggers that must be equal to fire.
/// </summary>
/// <typeparam name="TValue">The type of the trigger value.</typeparam>
/// <summary>
/// A base class for property triggers that must be equal to fire.
/// </summary>
/// <typeparam name="TValue">The type of the trigger value.</typeparam>
public class EqualsPropertyTrigger<TValue> : PropertyChangedTrigger
{
    /// <summary>
    /// Gets or sets the trigger value to match the property value for.
    /// </summary>
    /// <value>The trigger value.</value>
    public TValue TriggerValue { get; set; }

    /// <summary>
    /// Logic to check whether the trigger should fire.
    /// </summary>
    /// <param name="newValue">The new value.</param>
    /// <returns>True if the trigger should fire, otherwise false.</returns>
    protected override bool ShouldTriggerFire(object newValue)
    {
        if (newValue == null)
            return this.TriggerValue == null;

        return newValue.Equals(this.TriggerValue);
    }
}

So now we have a nice base class for our BooleanPropertyTrigger that makes it's implementation really nice and clean.

/// <summary>
/// A generic object property trigger
/// </summary>
public class PropertyTrigger : EqualsPropertyTrigger<object>
{ }

/// <summary>
/// A Boolean value property trigger
/// </summary>
public class BooleanPropertyTrigger : EqualsPropertyTrigger<bool>
{ }

/// <summary>
/// A string property value trigger
/// </summary>
public class StringPropertyTrigger : EqualsPropertyTrigger<string>
{ }

Now, all that's left to do is hook it up in our XAML by adding the namespace to our trigger and making sure we have a reference to System.Windows.Interactivity (version 4.0.5.0).

Next Steps

Next, we could make a NotEqualsPropertyTrigger that fires when a value is not a certain value. It's implementation would be as easy as inheriting from the EqualsPropertyTrigger and negating the base ShouldFireTrigger(...) method.

Hopefully, like me, you've learned a little about triggers and how they can be useful. For my next blog post I'm going to incorporate the visual state manager and make a GoToStateAction along with talking a little bit about creating the StoryBoardAction you see in the example.

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Clearable TextBox Custom Control

After some comments from Laurent Bugnion, of Galasoft and MVVM Light fame, I decided to try my hand at turning this simple little Clearable TextBox into a custom control for better "Skinability".

It looks like I've got most of the functionality replicated, including adding two states to help with animations.  The states are "Normal" and "Cleared".  By default, the Cleared state will cause the clear button text to flash red briefly.  You can also now set the ClearButtonTemplate and the ClearButtonContent if you want.  In the picture you can see I've set the ClearButtonContent to Clear and used the default template.

<clr:ClearableTextBox  
    Text="{Binding SomeText, Mode=TwoWay}"
    ClearButtonContent="Clear"
    VerticalAlignment="Top"/>

I haven't tested any custom state animations, only the default ones that are included.  Feel free to let me know if you find any problems. The source and binaries are available below.



Clearable TextBox Custom Control Source



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A Clearable TextBox for Win Phone 7

Update: I've updated this UserControl to a Custom Control for better templating and posted it for download. Check it out in the Clearable TextBox Custom Control post.



After seeing a tweet about the lack of a clearable text box similar to the IPhone by Eric Malamisura, I was inspired to whip together a simple control that fills this need.

Here is some code for the control, in case you don't want to download the full example. Just create a new UserControl called ClearableEditBox and paste these parts in the relevant places.

<!-- Put inside your new UserControl -->
<Grid x:Name="LayoutRoot">
    <TextBox
        MinWidth="50"
        Text="{Binding ElementName=uiThis, Path=Text, Mode=TwoWay}"
        x:Name="editBox"/>
        
    <Button
        MinWidth="30"
        HorizontalAlignment="Right"
        VerticalAlignment="Center"
        Click="clrBtn_Click"
        x:Name="clrBtn">
        <Button.Template>
            <ControlTemplate>
                <TextBlock                                
                    FontSize="25"            
                    Margin="0 0 20 0"
                    Foreground="Gray"            
                    FontWeight="Bold"
                    Text="X"/>
            </ControlTemplate>
        </Button.Template>
    </Button>
</Grid>

// Put inside your code behind for your new UserControl.
public partial class ClearableTextBox : UserControl, INotifyPropertyChanged
{
    public string Text
    {
        get { return (string)GetValue(TextProperty); }
        set { SetValue(TextProperty, value); }
    }

    // Using a DependencyProperty as the backing store for EditText.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty TextProperty =
        DependencyProperty.Register("Text", typeof(string), typeof(ClearableTextBox), new PropertyMetadata(string.Empty, HandleTextChanged));        

    public ClearableTextBox()
    {
        InitializeComponent();
    }

    private static void HandleTextChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
    {
        var box = obj as ClearableTextBox;
        if (null != box)
            box.OnPropertyChanged("Text");
    }

    private void clrBtn_Click(object sender, RoutedEventArgs e)
    {
        Text = string.Empty;
    }

    #region INotifyPropertyChanged Members

    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged(string name)
    {
        if (null != PropertyChanged)
            PropertyChanged(null, new PropertyChangedEventArgs(name));
    }

    #endregion
}

You can also download a sample project containing the control here.




Clearable TextBox UserControl



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