I have a text box with verticalscrollbarvisibility set to auto. I would like to do a test to find out if the scrollbar is actually visible during runtime. I have tried the statement:
if (textbox1.VerticalScrollBarVisibility == ScrollBarVisibility.Visible)
but it does not work. Any ideas?
First place the following extension method in static class (either place the class in the same namespace as the rest of your code or in namespace included with a using statement in your code file):-
public static IEnumerable<DependencyObject> Descendents(this DependencyObject root)
{
int count = VisualTreeHelper.GetChildrenCount(root);
for (int i = 0; i < count; i++)
{
var child = VisualTreeHelper.GetChild(root, i);
yield return child;
foreach (var descendent in Descendents(child))
yield return descendent;
}
}
With this extension method available you can dig out the ScrollViewer inside the text box which is responsible for the scroll bar and test its ComputedVerticalScrollBarVisibility.
if (textbox1.Descendents().OfType<ScrollViewer>()
.FirstOfDefault().ComputedVerticalScrollBarVisibility == Visibility.Visible)
Related
i want to set a value in a specific cell in wpf
and i use this code but getRow and getCell method show this error
'DataGrid' does not contain a definition for 'GetRow' and no extension method 'GetRow' accepting a first argument of type 'DataGrid' could be found (are you missing a using directive or an assembly reference?)
'DataGrid' does not contain a definition for 'GetCell' and no
extension method 'GetCell' accepting a first argument of type
'DataGrid' could be found (are you missing a using directive or an
assembly reference?) ControlSolution.Form
and error in public partial class UCfrmRaafaLevelsUp : UserControl
Extension method must be defined in a non-generic static class
the code i use it
public static T GetVisualChild<T>(Visual parent) where T : Visual
{
T child = default(T);
int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
for (int i = 0; i < numVisuals; i++)
{
Visual v = (Visual)VisualTreeHelper.GetChild(parent, i);
child = v as T;
if (child == null)
{
child = GetVisualChild<T>(v);
}
if (child != null)
{
break;
}
}
return child;
}
public static DataGridRow GetSelectedRow(this DataGrid grid)
{
return (DataGridRow)grid.ItemContainerGenerator.ContainerFromItem(grid.SelectedItem);
}
public static DataGridRow GetRow(this DataGrid grid, int index)
{
DataGridRow row = (DataGridRow)grid.ItemContainerGenerator.ContainerFromIndex(index);
if (row == null)
{
// May be virtualized, bring into view and try again.
grid.UpdateLayout();
grid.ScrollIntoView(grid.Items[index]);
row = (DataGridRow)grid.ItemContainerGenerator.ContainerFromIndex(index);
}
return row;
}
public static DataGridCell GetCell(this DataGrid grid, DataGridRow row, int column)
{
if (row != null)
{
DataGridCellsPresenter presenter = GetVisualChild<DataGridCellsPresenter>(row);
if (presenter == null)
{
grid.ScrollIntoView(row, grid.Columns[column]);
presenter = GetVisualChild<DataGridCellsPresenter>(row);
}
DataGridCell cell = (DataGridCell)presenter.ItemContainerGenerator.ContainerFromIndex(column);
return cell;
}
return null;
}
public static DataGridCell GetCell(this DataGrid grid, int row, int column)
{
DataGridRow rowContainer = grid.GetRow(row);
return grid.GetCell(rowContainer, column);
}
in this post
Change DataGrid cell value programmatically in WPF
Extension methods are the static methods that are called as instance methods on the type they were created. eg: the GetCell() method that you created. It uses the reference of DataGrid to call this method.
Such methods must be defined in a separate static class. Put these methods GetSelectedRow, GetCell, GetRow in a different static class and the code should work.
Extension methods need to be part of the inheritance chain. If your method is in a separate class (not DataGrid, and neither parent nor child of it), just make it normal static method, and call this method statically.
Logically, you cannot add an extension method to DataGrid itself nor its ancestor classes, and it doesn't seem like you are subclassing DataGrid, so this won't work.
I need to add some decoration to the contents of a WPF TextBox control. That works fine basically, I can get the position of specified character indices and layout my other elements accordingly. But it all breaks when the TextBox is scrolled. My layout positions don't match with the displayed text anymore because it has moved elsewhere.
Now I'm pretty surprised that the TextBox class doesn't provide any information about its scrolling state, nor any events when the scrolling has changed. What can I do now?
I used Snoop to find out whether there is some scrolling sub-element that I could ask, but the ScrollContentPresenter also doesn't have any scrolling information available. I'd really like to put my decoration elements right into the scrolled area so that the scrolling can affect them, too, but there can only be a single content control and that's one of the TextBox internals already.
I'm not sure how to capture an event when the textbox has been scrolled (probably use narohi's answer for that), but there is a simple way to see what the current scroll position is:
// Gets or sets the vertical scroll position.
textBox.VerticalOffset
(From http://msdn.microsoft.com/en-us/library/system.windows.controls.primitives.textboxbase.verticaloffset(v=vs.100).aspx)
I'm using it to see if the textbox is scrolled to the end, like this:
public static bool IsScrolledToEnd(this TextBox textBox)
{
return textBox.VerticalOffset + textBox.ViewportHeight == textBox.ExtentHeight;
}
You can get the ScrollViewer with this method by passing in your textbox as the argument and the type ScrollView. Then you may subscribe to the ScrollChanged event.
public static T FindDescendant<T>(DependencyObject obj) where T : DependencyObject
{
if (obj == null) return default(T);
int numberChildren = VisualTreeHelper.GetChildrenCount(obj);
if (numberChildren == 0) return default(T);
for (int i = 0; i < numberChildren; i++)
{
DependencyObject child = VisualTreeHelper.GetChild(obj, i);
if (child is T)
{
return (T)(object)child;
}
}
for (int i = 0; i < numberChildren; i++)
{
DependencyObject child = VisualTreeHelper.GetChild(obj, i);
var potentialMatch = FindDescendant<T>(child);
if (potentialMatch != default(T))
{
return potentialMatch;
}
}
return default(T);
}
Example:
public MainWindow()
{
InitializeComponent();
Loaded += new RoutedEventHandler(MainWindow_Loaded);
}
void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
ScrollViewer s = FindDescendant<ScrollViewer>(txtYourTextBox);
s.ScrollChanged += new ScrollChangedEventHandler(s_ScrollChanged);
}
void s_ScrollChanged(object sender, ScrollChangedEventArgs e)
{
// check event args for information needed
}
I have a TextBox in a WPF Project whose verticalscrollbar visibility is set to Auto. When I set a text in it at Runtime the vertical scroll bar becomes visible when text is more and vertical scroll bar hides when text is less.
What i want is if when i assign a large text to it (and verticalscrollbar becomes visible) then i will run a recursive loop which will reduce font size to a level till the scroll bar become hidden. I want to get the actual visibility value of verticalscrollbar.
In code behind the verticalscrollbarvisibility property always gives auto. (i think boz its set to auto in XAML).
// If my approach is wrong for this problem please let me know that also.
I found it. I passed my textbox in the function
ScrollViewer sv = FindVisualChild<ScrollViewer>(mytextbox);
if (sv != null)
{
// do something with ScrollViewer
}
public static T FindVisualChild<T>(DependencyObject depObj) where T : DependencyObject
{
if (depObj != null)
{
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(depObj, i);
if (child != null && child is T)
{
return (T)child;
}
T childItem = FindVisualChild<T>(child);
if (childItem != null) return childItem;
}
}
return null;
}
It returns me ScrollViewer whose visibility property is what i wanted.
I'm working on making an app come back nicely from being tombstoned. The app contains large listboxes, so I'd ideally like to scroll back to wherever the user was while they were scrolling around those listboxes.
It's easy to jump back to a particular SelectedItem - unfortunately for me, my app never needs the user to actually select an item, they're just scrolling through them. What I really want is some sort of MyListbox.ScrollPositionY but it doesn't seem to exist.
Any ideas?
Chris
You need to get hold of the ScrollViewer that is used by the ListBox internally so you can grab the value of the VerticalOffset property and subsequently call the SetVerticalOffset method.
This requires that you reach down from the ListBox through the Visual tree that makes up its internals.
I use this handy extension class which you should add to your project (I've gotta put this up on a blog because I keep repeating it):-
public static class VisualTreeEnumeration
{
public static IEnumerable<DependencyObject> Descendents(this DependencyObject root, int depth)
{
int count = VisualTreeHelper.GetChildrenCount(root);
for (int i = 0; i < count; i++)
{
var child = VisualTreeHelper.GetChild(root, i);
yield return child;
if (depth > 0)
{
foreach (var descendent in Descendents(child, --depth))
yield return descendent;
}
}
}
public static IEnumerable<DependencyObject> Descendents(this DependencyObject root)
{
return Descendents(root, Int32.MaxValue);
}
public static IEnumerable<DependencyObject> Ancestors(this DependencyObject root)
{
DependencyObject current = VisualTreeHelper.GetParent(root);
while (current != null)
{
yield return current;
current = VisualTreeHelper.GetParent(current);
}
}
}
With this available the ListBox (and all other UIElements for that matter) gets a couple of new extension methods Descendents and Ancestors. We can combine those with Linq to search for stuff. In this case you could use:-
ScrollViewer sv = SomeListBox.Descendents().OfType<ScrollViewer>().FirstOrDefault();
Does anybody have a good way of finding ALL the controls within an object that is of the same type? Here's my scenario, I have a tab control and within each tab control exists a user control (ALL of which match the same base type e.g. MyBaseClassControl). I want to be able to find that user control WITHOUT having to use the control.FindName("controlName") method, rather I would like to get a handle on the control by type (e.g. base class). The VisualTreeHelper class seems to do nothing for me as it only returns native Silverlight objects.
Given this:
public static IEnumerable<DependencyObject> AllChildren(this DependencyObject root)
{
var children = root.DirectChildren().ToList();
return children.Union(children.SelectMany(o => o.AllChildren()));
}
public static IEnumerable<DependencyObject> DirectChildren(this DependencyObject parent)
{
var childCount = VisualTreeHelper.GetChildrenCount(parent);
for (var i = 0; i < childCount; i++)
yield return System.Windows.Media.VisualTreeHelper.GetChild(parent, i);
}
You could do this:
myObj.AllChildren().OfType<MyBaseClassControl>();