How to get vertical offset from bottom to top in scrollviewer in uwp?

Question

I want scrollviewer vertical offset from bottom to top not top to bottom in uwp because it is only showing top to bottom as I increase the height of app from top it would'n work but when I decrease the height of app it would work...............please help me.

Here is my code

double getvalue = scrollviewer.verticaloffset;
textblock.Text = getvalue.ToString();

getting value but when i increase the height of app it wouldn't work but when i decrease the height the app it show some value.

when scrollbar is at the top it wouldn't give the value............................please help me guys.

guys here are some screenshots

Image 1

As you can see in the Image 1 when app is in normal state.

Image 2

As you can see in the Image 2 when app window height is small.

Image 3

As you can see in the Image 3 when I scroll up it shows Button.

Image 4

As you can see in the Image 4 When I increase the height of App it's not disappear.

Image 5

As you can see in the Image 5 When I decrease the height of App it's disappear.

So Guys can you please help me to make this feature possible

Answer 1

Based on the images and your description, I thought your purpose is to create a button which is used to let a ScrollViewer scroll to the top. The problem is how to let the button display when the ScrollViewer’s content is not at the bottom whenever you scroll up or down the bar or resize the window, and hide the button when when the ScrollViewer’s content is not at the bottom whenever you scroll up or down the bar or resize the window.

You could use VerticalOffset property which represents the distance the content has been scrolled vertically and ViewportHeight property which represents the vertical size of the viewable content and ExtentHeight property which represents the vertical size of all the scrollable content in the ScrollViewer, to determine whether the content of the ScrollViewer reach the bottom.

Please check the following code as a sample:

//MainPage.xaml
<Grid SizeChanged="Grid_SizeChanged">
    <ScrollViewer x:Name="scrollViewer" VerticalScrollBarVisibility="Visible" VerticalScrollMode="Enabled"
                  ViewChanged="scrollViewer_ViewChanged">
        <StackPanel x:Name="stackPanel" Background="LightGray">
            <TextBlock Text="0" Margin="20"/>
            <TextBlock Text="1" Margin="20"/>
            <TextBlock Text="2" Margin="20"/>
            <TextBlock Text="3" Margin="20"/>
            <TextBlock Text="4" Margin="20"/>
            <TextBlock Text="5" Margin="20"/>
            <TextBlock Text="6" Margin="20"/>
            <TextBlock Text="7" Margin="20"/>
            <TextBlock Text="8" Margin="20"/>
            <TextBlock Text="9" Margin="20"/>
            <TextBlock Text="10" Margin="20"/>
            <TextBlock Text="11" Margin="20"/>
            <TextBlock Text="12" Margin="20"/>
    </StackPanel>
    </ScrollViewer>

    <Button x:Name="BackButton" Content="top" Click="BackButton_Click" HorizontalAlignment="Center" VerticalAlignment="Bottom"/>
</Grid>

//MainPage.xaml.cs
private void BackButton_Click(object sender, RoutedEventArgs e)
{
    //The code is used to scroll to the top
    scrollViewer.ChangeView(null, 0, null);

    //the code is used to scroll to the bottom
    //scrollViewer.ChangeView(null, scrollViewer.ExtentHeight-scrollViewer.ViewportHeight, null);
}

private void scrollViewer_ViewChanged(object sender, ScrollViewerViewChangedEventArgs e)
{
    var verticalOffset = scrollViewer.VerticalOffset;
    var extentHeight = scrollViewer.ExtentHeight;
    var viewportHeight = scrollViewer.ViewportHeight;
    if (viewportHeight + verticalOffset == extentHeight)
    {
        BackButton.Visibility = Visibility.Collapsed;
    }
    else
    {
        BackButton.Visibility = Visibility.Visible;
    }
}

private void Grid_SizeChanged(object sender, SizeChangedEventArgs e)
{
    var verticalOffset = scrollViewer.VerticalOffset;
    var extentHeight = scrollViewer.ExtentHeight;
    var viewportHeight = scrollViewer.ViewportHeight;
    if (viewportHeight + verticalOffset == extentHeight)
    {
        BackButton.Visibility = Visibility.Collapsed;
    }
    else
    {
        BackButton.Visibility = Visibility.Visible;
    }
}

If you have any other concerns, please feel free to contact me.