WPF - Why is the last char not visible in keydown event method

Question

I have a WPF app where I'm updating output on key press. My code works fine. Only it feels a little bit behind as I'm using KeyUp event. When I try to use KeyDown, it is always a character behind. I have already tried adding UpdateSourceTrigger as shown in the TextBox XAML below

<TextBox 
    Text="{Binding TheLine, UpdateSourceTrigger=PropertyChanged}"
    Behaviors:WatermarkTextBoxBehavior.EnableWatermark="True"
    Behaviors:WatermarkTextBoxBehavior.Label="Please enter a numeric value"
    Behaviors:WatermarkTextBoxBehavior.LabelStyle="{StaticResource watermarkLabelStyle}" 
    Grid.Column="0" x:Name="txtLengthFrom" GotFocus="txtLengthFrom_GotFocus" FontSize="15" FontWeight="SemiBold"></TextBox>

All characters are available as expected in the KeyUp event. What can I do to make sure all characters are available in the KeyDown event?

The code behind looks like this

public MainWindow()
{
    InitializeComponent();
    this.KeyDown += new KeyEventHandler(MainWindow_KeyDown);
}

void MainWindow_KeyDown(object sender, KeyEventArgs e)
{
    UpdateOutput();
}

This is a strange way of doing things. Why would you need to attach a handler like that to update output? If you want something to happen when the contents of the textbox change, attach a handler to TextBox.TextChanged. — Jon
Huh! That gave me exactly what I wanted and code is simplified too. Thanks man. — strider

strider strider · Accepted Answer · 2014-02-28T23:32:49

Based on @Jon's comment, I changed my code to use TextBox.TextChanged event and it works as I want. So now when I keep a key pressed, the output is changing as characters gets added to text box. The way I had it, it would not update the output while I had a key pressed. I just didn't like it so was trying to fix that.

WPF - Why is the last char not visible in keydown event method

2 Answers