LiteObservableBehaviors 1.0.0

LiteObservableBehaviors

Lite version of WPF behaviors with fewer features but better performance and a smaller surface area.

Features

• Common WPF Behavior / TriggerAction implementations for MVVM bindings.
• Lightweight attached behavior patterns.
• Markup extensions for event-to-command bindings.
• XAML namespace: xmlns:lob="http://schemas.github.com/liteobservablebehaviors/2026/xaml".

Usage

Declare the library namespace and Microsoft.Xaml.Behaviors interactivity namespace in your XAML:

xmlns:i="http://schemas.microsoft.com/xaml/behaviors"
xmlns:b="http://schemas.github.com/liteobservablebehaviors/2026/xaml"

Background: why these two types exist

WPF TextBox exposes properties such as SelectionStart, SelectionLength, SelectedText, and CaretIndex, but they are not dependency properties, so they cannot be bound to a ViewModel through ordinary bindings.

LiteObservableBehaviors addresses this with two complementary types:

Each instance binds a single property via its Property and Source members.

TextBoxSetStateToControlBehavior

One-way binding from ViewModel to TextBox

When a ViewModel property changes, this behavior writes the new value onto a non-bindable TextBox property such as SelectionStart, SelectionLength, SelectedText, or CaretIndex. Attach one instance per property inside Interaction.Behaviors.

XAML example

<TextBox>
    <i:Interaction.Behaviors>
        <b:TextBoxSetStateToControlBehavior
            Property="SelectionStart"
            Source="{Binding CaretPosition}" />
        <b:TextBoxSetStateToControlBehavior
            Property="SelectionLength"
            Source="{Binding SelectionLen}" />
    </i:Interaction.Behaviors>
</TextBox>

Behavior

When ViewModel properties such as CaretPosition or SelectionLen raise change notifications (INotifyPropertyChanged), the corresponding TextBox properties are updated automatically.

TextBoxSetStateToSourceAction

One-way push from TextBox to ViewModel

When the user interacts with the TextBox (for example, by changing the selection), this trigger action reads the current control state and writes it to the ViewModel. Place it inside Interaction.Triggers and invoke it from the appropriate event.

XAML example

<TextBox>
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="SelectionChanged">
            <b:TextBoxSetStateToSourceAction
                Property="SelectionStart"
                Source="{Binding CaretPosition, Mode=OneWayToSource}" />
            <b:TextBoxSetStateToSourceAction
                Property="SelectionLength"
                Source="{Binding SelectionLen, Mode=OneWayToSource}" />
        </i:EventTrigger>
    </i:Interaction.Triggers>
</TextBox>

Behavior

Each time SelectionChanged fires, the current SelectionStart and SelectionLength values are written to the bound ViewModel properties.

Combined example (near two-way sync)

Use both types together to approximate two-way synchronization:

<TextBox>

    
    <i:Interaction.Behaviors>
        <b:TextBoxSetStateToControlBehavior
            Property="SelectionStart"
            Source="{Binding CursorPos}" />
        <b:TextBoxSetStateToControlBehavior
            Property="SelectionLength"
            Source="{Binding SelLen}" />
    </i:Interaction.Behaviors>

    
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="SelectionChanged">
            <b:TextBoxSetStateToSourceAction
                Property="SelectionStart"
                Source="{Binding CursorPos, Mode=OneWayToSource}" />
            <b:TextBoxSetStateToSourceAction
                Property="SelectionLength"
                Source="{Binding SelLen, Mode=OneWayToSource}" />
        </i:EventTrigger>
    </i:Interaction.Triggers>

</TextBox>

TextBoxBindingSupportBehavior vs SetState types

For TextBox and PasswordBox, TextBoxBindingSupportBehavior offers a simpler approach: bind SelectedText, SelectionLength, and SelectionStart directly with two-way bindings:

<TextBox>
    <i:Interaction.Behaviors>
        <b:TextBoxBindingSupportBehavior
            SelectedText="{Binding SelectedText}"
            SelectionLength="{Binding SelectionLength}"
            SelectionStart="{Binding SelectionStart}" />
    </i:Interaction.Behaviors>
</TextBox>

Prefer TextBoxBindingSupportBehavior when those three properties are all you need. Use the SetStateTo... types when you need other TextBox-specific state (for example CaretIndex) or want finer control over which events drive updates.

Summary

• TextBoxSetStateToControlBehavior — add to Behaviors; reflects ViewModel changes on the TextBox (VM → View).
• TextBoxSetStateToSourceAction — add inside Triggers; sends TextBox state to the ViewModel on events (View → VM).
• For common two-way binding of SelectedText, SelectionLength, and SelectionStart, TextBoxBindingSupportBehavior is the simpler choice.

Project layout

License

MIT