Show / hide textblock on a WPF window for some fixed time interval and in random position

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1.80/5 (2 votes)

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Hi. i'm facing problem in achieving below things using WPF, XAML / c# -
1. Need to hide a textblock for 3 seconds and show it for 2 seconds on a window
2. It's position should be random every time it shows on the window.
Please help me out..

What I have tried:

I tried following but it's giving desired result -

<TextBlock Foreground="Red" Text="Some Information">
	<TextBlock.Triggers>
		<EventTrigger  RoutedEvent="Window.Loaded">
			<BeginStoryboard>
				<Storyboard>
					<DoubleAnimation Storyboard.TargetProperty="(TextBlock.Opacity)"
						From="1" 
						To="0" 
						AutoReverse="True"
						BeginTime="0:0:0" 
						Duration="0:0:.125"
						RepeatBehavior="Forever">
					</DoubleAnimation>
				</Storyboard>
			</BeginStoryboard>
		</EventTrigger>
	</TextBlock.Triggers>
</TextBlock>

Posted 18-Apr-17 21:25pm

Vijayakumara Nv

Updated 20-Apr-17 12:50pm

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2 solutions

Solution 3

You should use the Visibility property to show and hide the control. That said, you had the right idea going for the EventTrigger. Use ObjectAnimationUsingKeyFrames for the Visibility property. After 2 seconds the TextBlock will collapse (become hidden), then 3 seconds later it will become visible again.

<TextBlock.Triggers>
	<EventTrigger  RoutedEvent="Window.Loaded">
		<BeginStoryboard>
			<Storyboard>
                <ObjectAnimationUsingKeyFrames 
                    Storyboard.TargetProperty="Visibility"
                    RepeatBehavoir="Forever">
                    <DiscreteObjectKeyFrame KeyTime="0:0:2" 
                        Value="{x:Static Visibility.Collapsed}"/>
                    <DiscreteObjectKeyFrame KeyTime="0:0:5" 
                        Value="{x:Static Visibility.Visible}"/>
                </ObjectAnimationUsingKeyFrames>
			</Storyboard>
		</BeginStoryboard>
	</EventTrigger>
</TextBlock.Triggers>

For the random positioning TextBlock has an IsVisibleChanged event that you can use. I added this C# code to that event. The event will trigger every time the storyboard changes the Visiblity. Note that I didn't bother updating the position in a separate thread. This is because when the storyboard changes the Visibility again the control has to be re-rendered and the new position values are used when that happens.

private void UpdatePostion(object sender, DependencyPropertyChangedEventArgs e)
{
    FrameworkElement tb = (FrameworkElement)sender;
    Random rnd = new Random();
    double tbHeight = tb.Height;
    double tbWidth = tb.width;
    Thickness tbMargin = tb.Margin;

    // mygrid is the name of the container my TextBlock is in
    double GridHeight = myGrid.ActualHeight;
    double GridWidth = myGrid.ActualWidth;

    // only update postion when the control is collapsed
    if (tb.Visibility != Visibility.Collapsed)
        return;

    tbMargin.Top = (double)(rnd.Next(0, (int)(GridHeight - tbHeight)));
    tbMargin.Width = (double)(rnd.Next(0, (int)(GridWidth - tbWidth)));
    tb.Margin = tbMargin;
}

Posted 20-Apr-17 12:50pm

Angelo L

Updated 20-Apr-17 13:02pm

v5

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Mahesh Alappuzha · Accepted Answer · 2017-04-20T01:56:00

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        private Timer tmr;
        public MainWindow ( )
        {
            InitializeComponent ( );
            tmr = new Timer {Interval = 3*1000};
            tmr.Elapsed +=tmr_Elapsed;
            tmr.Start ( );
        }

        private void tmr_Elapsed (object sender , ElapsedEventArgs e)
        {
            Application.Current.Dispatcher.Invoke ( GetValue );
        }

        private void GetValue()
        {
            if (tmr.Interval == 3*1000)
            {
                txtSample.Visibility = Visibility.Collapsed;
                tmr.Interval = 2*1000;
            }
            else
            {
                txtSample.Visibility = Visibility.Visible;
                tmr.Interval = 3*1000;
            }
        }
    }
}