#621 – An Example of Handling Preview Keypress Events

Below is an example of handling both PreviewKeyUp and KeyUp events.  The PreviewKeyUp is used to completely block a particular key (the letter ‘E’).  The KeyUp event is used to trigger an update to a calculated property.

    <StackPanel Orientation="Vertical">
        <StackPanel Orientation="Horizontal"
                    PreviewKeyDown="StackPanel_PreviewKeyUp">
            <Label Content="First Name:" VerticalAlignment="Center"/>
            <TextBox Margin="5" Width="100" Height="25"
                     Text="{Binding Path=FirstName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
                     KeyUp="txtFirst_KeyUp"/>
            <Label Content="Last Name:" VerticalAlignment="Center"/>
            <TextBox Margin="5" Width="100" Height="25"
                     Text="{Binding Path=LastName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
                     KeyUp="txtLast_KeyUp"/>
        </StackPanel>
        <Label Content="{Binding FullName}"/>
        <Label Content="{Binding LastChanged}"/>
    </StackPanel>

    public partial class MainWindow : Window, INotifyPropertyChanged
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }

        public string FullName { get; set; }
        public string LastChanged { get; set; }

        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = this;
            CalcFullName();
        }

        private void StackPanel_PreviewKeyUp(object sender, KeyEventArgs e)
        {
            // E's are not allowed !
            if (e.Key == Key.E)
                e.Handled = true;
        }

        private void txtFirst_KeyUp(object sender, KeyEventArgs e)
        {
            CalcFullName();
            LastChanged = "Changing FIRST Name";
            RaisePropertyChanged("LastChanged");
        }

        private void txtLast_KeyUp(object sender, KeyEventArgs e)
        {
            CalcFullName();
            LastChanged = "Changing LAST Name";
            RaisePropertyChanged("LastChanged");
        }

        private void CalcFullName()
        {
            FullName = string.Format("Full Name: [{0} {1}]", FirstName, LastName);
            RaisePropertyChanged("FullName");
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void RaisePropertyChanged(string prop)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(prop));
        }

    }