I want to modify the content in a TabItem of a TabView. And that TabItem uses DataTemplate.
When I am trying to access the children of that item like the following:
var container = tabview.ContainerFromIndex(tabview.SelectedIndex);
int count = VisualTreeHelper.GetChildrenCount(container);
I got the ArgumentException: Wrong Parameter Reference on the second line. How should I use VisualTreeHelper to modify it?
Here is a easy method:
public static T GetChildObject<T>(DependencyObject obj, string name) where T : FrameworkElement
{
DependencyObject child = null;
T grandChild = null;
for (int i = 0; i <= VisualTreeHelper.GetChildrenCount(obj) - 1; i++)
{
child = VisualTreeHelper.GetChild(obj, i);
if (child is T && (((T)child).Name == name | string.IsNullOrEmpty(name)))
{
return (T)child;
}
else
{
grandChild = GetChildObject<T>(child, name);
}
if (grandChild != null)
{
return grandChild;
}
}
return null;
}
From your description, you can already get the container of the target element. Let's assume that the element you need is named TargetEle and the type is TextBlock. You can write it like this:
var target = GetChildObject<TextBlock>(container,"TargetEle");
Update
I tested your code and found that you didn't capture the events loaded by the page.
In fact, the SelectionChanged event is fired when the TabView is just created, but the visual tree is not loaded yet, and you can't get the content from it through the code. You can create an IsLoaded property in the page, set it to True when Page Loaded, and determine this property in the SelectionChanged time.
Only when it is True, proceed to the next step.
I would like to find all of the controls within a WPF control specially in Datagrid, DataGridTemplateColumn. I have had a look at a lot of samples and it seems that they all either require a Name to be passed as parameter or simply do not work.
What have you tried that "require a name to be passed or simply don't work" and what's wrong with the former?
private void FindAllChildren()
{
var depObj = dataGrid;
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(depObj, i);
if (child is DataGridTemplateColumn)
{
// do a thing
}
}
}
Adapted from here: https://stackoverflow.com/a/978352/1189566
I have a ListView which might contains a lot of items, so it is virtualized and recycling items. It does not use sort. I need to refresh some value display, but when there are too many items, it is too slow to update everything, so I would like to refresh only the visible items.
How could I get a list of all currently displayed items ? I tried to look into the ListView or in the ScrollViewer, but I still have no idea how to achieve this. The solution must NOT go through all items to test if they can be seen, because this would be too slow.
I'm not sure code or xaml would be useful, it is just a Virtualized/Recycling ListView with its ItemSource bound to an Array.
Edit :
Answer :
thanks to akjoshi, I found the way :
get the ScrollViewer of the ListView
(with a FindDescendant method, that you can do yourself with the VisualTreeHelper ).
read its ScrollViewer.VerticalOffset : it is the number of the first item shown
read its ScrollViewer.ViewportHeight : it is the count of items shown.
Rq : CanContentScroll must be true.
Have a look at this question on MSDN showing a technique to find out the visible ListView items -
How to find the rows (ListViewItem(s)) in a ListView that are actually visible?
Here's the relevant code from that post -
listView.ItemsSource = from i in Enumerable.Range(0, 100) select "Item" + i.ToString();
listView.Loaded += (sender, e) =>
{
ScrollViewer scrollViewer = listView.GetVisualChild<ScrollViewer>(); //Extension method
if (scrollViewer != null)
{
ScrollBar scrollBar = scrollViewer.Template.FindName("PART_VerticalScrollBar", scrollViewer) as ScrollBar;
if (scrollBar != null)
{
scrollBar.ValueChanged += delegate
{
//VerticalOffset and ViweportHeight is actually what you want if UI virtualization is turned on.
Console.WriteLine("Visible Item Start Index:{0}", scrollViewer.VerticalOffset);
Console.WriteLine("Visible Item Count:{0}", scrollViewer.ViewportHeight);
};
}
}
};
Another thing you should do is to use ObservableCollection as your ItemSource instead of an Array; that will definitely improve the performance.
Update:
Ya that might be true(array vs. ObservableCollection) but I would like to see some statistics related to this;
The real benefit of ObservableCollection is if you have a requirement to add/remove items from your ListView at run-time, in case of an Array you will have to reassign the ItemSource of ListView and the ListView first throws away its previous items and regenerates its entire list.
After trying to figure out something similar, I thought I would share my result here (as it seems easier than the other responses):
Simple visibility test I got from here.
private static bool IsUserVisible(FrameworkElement element, FrameworkElement container)
{
if (!element.IsVisible)
return false;
Rect bounds =
element.TransformToAncestor(container).TransformBounds(new Rect(0.0, 0.0, element.ActualWidth, element.ActualHeight));
var rect = new Rect(0.0, 0.0, container.ActualWidth, container.ActualHeight);
return rect.Contains(bounds.TopLeft) || rect.Contains(bounds.BottomRight);
}
Afterwards you can loop through the listboxitems and use that test to determine which are visible. Since the listboxitems are always ordered the same the first visible one in this list would be the first visible one to the user.
private List<object> GetVisibleItemsFromListbox(ListBox listBox, FrameworkElement parentToTestVisibility)
{
var items = new List<object>();
foreach (var item in PhotosListBox.Items)
{
if (IsUserVisible((ListBoxItem)listBox.ItemContainerGenerator.ContainerFromItem(item), parentToTestVisibility))
{
items.Add(item);
}
else if (items.Any())
{
break;
}
}
return items;
}
How I see things :
on one side, you have your data. They must be up to date, because this is where your information is in memory. Iterating on your data list should be pretty fast, and most of all, can be done on another thread, in background
on the other side, you have the display. Your ListView already make the trick of refreshing only the datas displayed, since it's virtualizing ! You need no more tricks, it's already in place !
On last work, using a binding on an ObservableCollection is a good advice. If you intend to modify the ObservableCollection from an another thread, I would recommend this : http://blog.quantumbitdesigns.com/2008/07/22/wpf-cross-thread-collection-binding-part-1/
I spend a lot of time finding a better solution for this,
In my situation i have a scrollviewer, filled with items with custom heigths that can be set visible/invisible, i came up with this. It does the same as above solutions but with a fraction of the CPU. I hope it helps some one.
The first items of the listview / scrollpanel is TopVisibleItem
public int TopVisibleItem { get; private set; }
private double CurrentDistance;
private void TouchScroller_ScrollChanged(object sender, ScrollChangedEventArgs e)
{
if (myItemControl.Items.Count > 0)
{
MoveDirection direction = (MoveDirection)Math.Sign(e.VerticalChange);
if (direction == MoveDirection.Positive)
while (CurrentDistance < e.VerticalOffset && TopVisibleItem < myItemControl.Items.Count)
{
CurrentDistance += ((FrameworkElement)myItemControl.Items[TopVisibleItem]).ActualHeight;
TopVisibleItem += 1;
}
else
while (CurrentDistance >= e.VerticalOffset && TopVisibleItem > 0)
{
CurrentDistance -= ((FrameworkElement)myItemControl.Items[TopVisibleItem]).ActualHeight;
TopVisibleItem -= 1;
}
}
}
public enum MoveDirection
{
Negative = -1,
Positive = 1,
}
If you have a virtualization enabled ListView, Then you can get all Current Visible items as below:
Get VirtualizingStackPanel
Get all ListViewItems in VirtualizingStackPanel
The code is shown below.
VirtualizingStackPanel virtualizingStackPanel = FindVisualChild<VirtualizingStackPanel>(requiredListView);
List<ListViewItem> items = GetVisualChildren<ListViewItem>(virtualizingStackPanel);
The Functions are shown below.
private childItem FindVisualChild<childItem>(DependencyObject obj) where childItem : DependencyObject
{
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(obj, i);
if (child != null && child is childItem)
return (childItem)child;
else
{
childItem childOfChild = FindVisualChild<childItem>(child);
if (childOfChild != null)
return childOfChild;
}
}
return null;
}
private List<childItem> GetVisualChildren<childItem>(DependencyObject obj) where childItem : DependencyObject
{
List<childItem> childList = new List<childItem>();
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(obj, i);
if (child != null && child is childItem)
childList.Add(child as childItem);
}
if (childList.Count > 0)
return childList;
return null;
}
This will return you list of current ListViewItem loaded for displaying.
Hope it helps :).
I have the following code that is supposed to find an element inside of something. The problem is that I have a DataGrid, whose first column has a CheckBox in it's header. The checkbox itself is defined in a Style, which exists in the <controls:ChildWindow.Resources> dictionary of the parent child window.
At runtime, if all elements of the binding collection of the grid are "selected", than I need to select the damn checkbox. However, since the checkbox exists in the style it is not easily accesible and thus I need to walk through the entire DOM to find the specific checkbox.
This is the code that makes the DOM Traversal. It is implemented as an extension method to FrameworkElement so I can call the FindElement or GetChildren methods from any control that inherits from FrameworkElement:
public static class FrameworkElementExtensions
{
public static FrameworkElement FindElement(this FrameworkElement parentFrameworkElement, string childFrameworkElementNameToSearch)
{
FrameworkElement childFrameworkElementFound = null;
parentFrameworkElement.SearchElements(ref childFrameworkElementFound, childFrameworkElementNameToSearch);
return childFrameworkElementFound;
}
public static List<FrameworkElement> GetChildren(this FrameworkElement parentElement)
{
List<FrameworkElement> childFrameworkElementsFound = new List<FrameworkElement>();
parentElement.GetChildren(childFrameworkElementsFound);
return childFrameworkElementsFound;
}
public static void SearchElements(this FrameworkElement parentFrameworkElement, ref FrameworkElement childFrameworkElementToFind, string childFrameworkElementName)
{
int childrenCount = VisualTreeHelper.GetChildrenCount(parentFrameworkElement);
if (childrenCount > 0)
{
FrameworkElement childFrameworkElement = null;
for (int i = 0; i < childrenCount; i++)
{
childFrameworkElement = (FrameworkElement)VisualTreeHelper.GetChild(parentFrameworkElement, i);
if (childFrameworkElement != null && childFrameworkElement.Name.Equals(childFrameworkElementName))
{
childFrameworkElementToFind = childFrameworkElement;
return;
}
childFrameworkElement.SearchElements(ref childFrameworkElementToFind, childFrameworkElementName);
}
}
}
public static void GetChildren(this FrameworkElement parentFrameworkElement, List<FrameworkElement> allChildFrameworkElement)
{
int childrenCount = VisualTreeHelper.GetChildrenCount(parentFrameworkElement);
if (childrenCount > 0)
{
for (int i = 0; i < childrenCount; i++)
{
FrameworkElement childFrameworkElement = (FrameworkElement)VisualTreeHelper.GetChild(parentFrameworkElement, i);
allChildFrameworkElement.Add(childFrameworkElement);
childFrameworkElement.GetChildren(allChildFrameworkElement);
}
}
}
}
So the issue at hand is that when i call something along the lines of SomeDataGrid.FindElement("HeaderCheckBox"); it always returns a null. The assumption here is that I have a DataGrid called SomeDataGrid and a CheckBox defined within a style called HeaderCheckBox.
Upon further debugging I also found out that no matter what control I call these extension methods from, the VisualTreeHelper.GetChildrenCount method call used in the last two methods in my code always returns 0 ??? WTF?
Anyone has any idea on how to fix this?
Thanks,
Martin
Sure, no problem. Here it is.
It was made with VS2010 and Silverlight 4... just in case.
sorry about not making myself clear enough and not putting enough effort (wont happen again :)). i'm building a form App where users have to fill out the form. i have a TabControl with 3 TabItem one of the TabItem has TextBoxes the second has TextBoxes and RadioButton and third has only CheckBoxes. i have written a code to dictect error by on clicking submit using ValidationRule/ValidationResult and and using GroupBinding (got it from msdn samples). now the problem am having is code to search through the tabs, compare the controls (e.g. controlA,controlB) to know wich one comes before the other and return the tabindex. one of the use i want with this is letting the user jump to the uncompleted TextBox,RadioButton or CheckBoxes in order like starting from the first Tabitem in the TabControl
with this code i could work the tree to locate the controls(code from Philipp Sumi blog but i modified it a little)
private void Button_Click(
object sender,
RoutedEventArgs e)
{
IEnumerator enumerator = FindLogicalChildren(_parentStackPanel).GetEnumerator();
while (enumerator.MoveNext())
MessageBox.Show(enumerator.Current.ToString());
}
private IEnumerable FindLogicalChildren(
DependencyObject depObj)
{
if (depObj != null)
{
foreach (object childObj in LogicalTreeHelper.GetChildren(depObj))
{
DependencyObject child = childObj as DependencyObject;
if (child != null && child is Control)
{
yield return (Control)child;
}
foreach (Control childOfChild in FindLogicalChildren(child))
{
yield return childOfChild;
}
}
}
}
but i dodnt know how continue to get the tabindex of each control in order form as i work down the tree. can any one please help me on this? Thanks
im using this method:
private int Compare(
Control controlA,
Control controlB)
{
DependencyObject commonAncestor = controlA.FindCommonVisualAncestor(controlB);
for (int index = 0; index < VisualTreeHelper.GetChildrenCount(commonAncestor); index++)
{
Visual childVisual = (Visual)VisualTreeHelper.GetChild(commonAncestor, index);
Control control = (Control)childVisual;
control.TabIndex = index;
}
return controlA.TabIndex.CompareTo(controlB.TabIndex);
}
that returns 1,-1 or 0 to compare two controls to find out which one comes before the other. the question is, can anyone tell me a better way of doing this.