treeview interview questions
Top treeview frequently asked interview questions
What are some of the better AJAX Treeviews out there that support asynchronous JSON loading.
YUI TreeView seems nice, but bloated with tables, etc.
Source: (StackOverflow)
Can anybody help me out with how to enable a treeview to scroll? There must be a simple way but I can't make it work in my code. After multiple failed tries, I currently have something like this:
<ScrollViewer CanContentScroll="True">
<TreeView ...>
</TreeView>
</ScrollViewer>
I do see an 'disabled' scrollbar, but when the notes of the treeview are larger than the screen height, no scrolling is activated.
Source: (StackOverflow)
When I expand items in my treeview so that scrolling is necessary, a scrollbar appears. However, it doesn't scroll down for the newly expanded branch of items - they get cropped by the bottom of the control. So as I continue expanding items at the bottom of the tree, I have to keep manually scrolling down to see the new children. Anyone have a suggestion for how make it automatically scroll to show the newly expanded items?
Source: (StackOverflow)
How is it possible to programmatically select an item in a WPF TreeView? The ItemsControl model seems to prevent it.
Source: (StackOverflow)
I know there is the ExpandableListView but it only supports up to 2 levels. I need a true treeview vertical list with at least up to ~5 levels (more is better).
Any suggestions?
edit:
I see talk about using a Custom Adapter and setting the padding based on the items level.
I have an unsorted ArrayList of objects that have an ID and parent ID, and I dynamically add items to this array as well.
Can anyone give me some examples of how I can go about doing this?
Source: (StackOverflow)
The System.Web.UI.WebControls.TreeView class offers this event, but the Forms version of TreeView doesn't. What's the equivalent in the Forms world? I'm using AfterSelect but it doesn't seem quite right. Maybe it is in fact what I'm looking for but the documentation is a bit hazy.
Source: (StackOverflow)
If virtualizing is enabled in TreeView with items having various sizes, multiple problems appear:
Vertical scroll bar changes its size randomly and doesn't remember sizes of elements after viewing the whole tree. Scrolling with mouse is hard.
After some scrolling up and down, ArgumentNullException is thrown from the framework code.
Reproduciing is simple: create a new WPF application, then put this code into MainWindow.xaml
<Window x:Class="VirtualTreeView.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="800" Width="400" Left="0" Top="0"
DataContext="{Binding RelativeSource={RelativeSource Self}}">
<Grid>
<TreeView x:Name="tvwItems" ItemsSource="{Binding Items}"
VirtualizingPanel.IsVirtualizing="True" VirtualizingPanel.VirtualizationMode="Recycling">
<TreeView.ItemTemplate>
<DataTemplate>
<Border Height="{Binding Height}" Width="{Binding Height}"
BorderThickness="1" Background="DarkGray" BorderBrush="DarkBlue"/>
</DataTemplate>
</TreeView.ItemTemplate>
</TreeView>
</Grid>
</Window>
and this code into MainWindow.xaml.cs
using System.Collections.ObjectModel;
using System.Linq;
namespace VirtualTreeView
{
public partial class MainWindow
{
public ObservableCollection<Item> Items { get; set; }
public MainWindow ()
{
Items = new ObservableCollection<Item>(Enumerable.Range(0, 20).Select(i => new Item {
Height = i*20,
}));
InitializeComponent();
}
}
public class Item
{
public double Height { get; set; }
}
}
When application is ran, move mouse cursor into a treeview, scroll to the bottom using mouse wheel, then scroll to the top, then start scrolling down again. Somewhere in the middle the following exception is thrown:
System.ArgumentNullException was unhandled
HResult=-2147467261
Message=Value cannot be null.
Parameter name: element
Source=PresentationCore
ParamName=element
StackTrace:
at MS.Internal.Media.VisualTreeUtils.AsNonNullVisual(DependencyObject element, Visual& visual, Visual3D& visual3D)
at System.Windows.Media.VisualTreeHelper.GetParent(DependencyObject reference)
at System.Windows.Controls.VirtualizingStackPanel.FindScrollOffset(Visual v)
at System.Windows.Controls.VirtualizingStackPanel.OnAnchorOperation(Boolean isAnchorOperationPending)
at System.Windows.Controls.VirtualizingStackPanel.OnAnchorOperation()
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.DispatcherOperation.InvokeImpl()
at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Windows.Threading.DispatcherOperation.Invoke()
at System.Windows.Threading.Dispatcher.ProcessQueue()
at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
at System.Windows.Threading.Dispatcher.Run()
at System.Windows.Application.RunDispatcher(Object ignore)
at System.Windows.Application.RunInternal(Window window)
at System.Windows.Application.Run(Window window)
at System.Windows.Application.Run()
at VirtualTreeView.App.Main() in d:\Docs\Projects\_Try\VirtualTreeView\obj\Debug\App.g.cs:line 0
at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
You can also see that exception is not the only problem. When scrolling up and down, scroll bar constantly changes its size. (The same problem doesn't appear in ListBox which can't predict size, but remembers total height after viewing the whole list.)
Question: How to make the scroll bar behave properly and get rid of the exception? (I don't mind links to alternative TreeView controls or maybe virtualizing panels which support this scenario.)
Source: (StackOverflow)
How can I retrieve the item that is selected in a WPF-treeview? I want to do this in XAML, because I want to bind it.
You might think that it is SelectedItem but apparently that does not exist is readonly and therefore unusable.
This is what I want to do:
<TreeView ItemsSource="{Binding Path=Model.Clusters}"
ItemTemplate="{StaticResource ClusterTemplate}"
SelectedItem="{Binding Path=Model.SelectedCluster}" />
I want to bind the SelectedItem to a property on my Model.
But this gives me the error:
'SelectedItem' property is read-only and cannot be set from markup.
Edit:
Ok, this is the way that I solved this:
<TreeView
ItemsSource="{Binding Path=Model.Clusters}"
ItemTemplate="{StaticResource HoofdCLusterTemplate}"
SelectedItemChanged="TreeView_OnSelectedItemChanged" />
and in the codebehindfile of my xaml:
private void TreeView_OnSelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
Model.SelectedCluster = (Cluster)e.NewValue;
}
Source: (StackOverflow)
The selected item in a WPF TreeView has a dark blue background with "sharp" corners. That looks a bit dated today:
I would like to change the background to look like in Explorer of Windows 7 (with/without focus):
What I tried so far does not remove the original dark blue background but paints a rounded border on top of it so that you see the dark blue color at the edges and at the left side - ugly.
Interestingly, when my version does not have the focus, it looks pretty OK:
I would like to refrain from redefining the control template as shown here or here. I want to set the minimum required properties to make the selected item look like in Explorer.
Alternative: I would also be happy to have the focused selected item look like mine does now when it does not have the focus. When losing the focus, the color should change from blue to grey.
Here is my code:
<TreeView
x:Name="TreeView"
ItemsSource="{Binding TopLevelNodes}"
VirtualizingStackPanel.IsVirtualizing="True"
VirtualizingStackPanel.VirtualizationMode="Recycling">
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
<Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
<Style.Triggers>
<Trigger Property="IsSelected" Value="True">
<Setter Property="BorderBrush" Value="#FF7DA2CE" />
<Setter Property="Background" Value="#FFCCE2FC" />
</Trigger>
</Style.Triggers>
</Style>
</TreeView.ItemContainerStyle>
<TreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type viewmodels:ObjectBaseViewModel}" ItemsSource="{Binding Children}">
<Border Name="ItemBorder" CornerRadius="2" Background="{Binding Background, RelativeSource={RelativeSource AncestorType=TreeViewItem}}"
BorderBrush="{Binding BorderBrush, RelativeSource={RelativeSource AncestorType=TreeViewItem}}" BorderThickness="1">
<StackPanel Orientation="Horizontal" Margin="2">
<Image Name="icon" Source="/ExplorerTreeView/Images/folder.png"/>
<TextBlock Text="{Binding Name}"/>
</StackPanel>
</Border>
</HierarchicalDataTemplate>
</TreeView.Resources>
</TreeView>
Solution
With the excellent answers of Sheridan and Meleak my TreeView now looks like this in code (a result I am very happy with and which is pretty near Explorer's style):
<TreeView
...
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<!-- Style for the selected item -->
<Setter Property="BorderThickness" Value="1"/>
<Style.Triggers>
<!-- Selected and has focus -->
<Trigger Property="IsSelected" Value="True">
<Setter Property="BorderBrush" Value="#7DA2CE"/>
</Trigger>
<!-- Mouse over -->
<Trigger Property="helpers:TreeView_IsMouseDirectlyOverItem.IsMouseDirectlyOverItem" Value="True">
<Setter Property="Background">
<Setter.Value>
<LinearGradientBrush EndPoint="0,1" StartPoint="0,0">
<GradientStop Color="#FFFAFBFD" Offset="0"/>
<GradientStop Color="#FFEBF3FD" Offset="1"/>
</LinearGradientBrush>
</Setter.Value>
</Setter>
<Setter Property="BorderBrush" Value="#B8D6FB"/>
</Trigger>
<!-- Selected but does not have the focus -->
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="IsSelected" Value="True"/>
<Condition Property="IsSelectionActive" Value="False"/>
</MultiTrigger.Conditions>
<Setter Property="BorderBrush" Value="#D9D9D9"/>
</MultiTrigger>
</Style.Triggers>
<Style.Resources>
<Style TargetType="Border">
<Setter Property="CornerRadius" Value="2"/>
</Style>
</Style.Resources>
</Style>
</TreeView.ItemContainerStyle>
<TreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type viewmodels:ObjectBaseViewModel}" ItemsSource="{Binding Children}">
<StackPanel Orientation="Horizontal" Margin="2,1,5,2">
<Grid Margin="0,0,3,0">
<Image Name="icon" Source="/ExplorerTreeView/Images/folder.png"/>
</Grid>
<TextBlock Text="{Binding Name}" />
</StackPanel>
</HierarchicalDataTemplate>
<!-- Brushes for the selected item -->
<LinearGradientBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" EndPoint="0,1" StartPoint="0,0">
<GradientStop Color="#FFDCEBFC" Offset="0"/>
<GradientStop Color="#FFC1DBFC" Offset="1"/>
</LinearGradientBrush>
<LinearGradientBrush x:Key="{x:Static SystemColors.ControlBrushKey}" EndPoint="0,1" StartPoint="0,0">
<GradientStop Color="#FFF8F8F8" Offset="0"/>
<GradientStop Color="#FFE5E5E5" Offset="1"/>
</LinearGradientBrush>
<SolidColorBrush x:Key="{x:Static SystemColors.HighlightTextBrushKey}" Color="Black" />
<SolidColorBrush x:Key="{x:Static SystemColors.ControlTextBrushKey}" Color="Black" />
</TreeView.Resources>
</TreeView>
Source: (StackOverflow)
How can I find out which node in a tree list the context menu has been activated? For instance right-clicking a node and selecting an option from the menu.
I can't use the TreeViews' SelectedNode property because the node is only been right-clicked and not selected.
Source: (StackOverflow)
I'm working on a JavaScript dynamically loaded tree view user control. I'd like to test it with real world data.
Does anybody know any public service with an API that provides access to hierarchical data in JSON format?
Source: (StackOverflow)
I'm using the following code to make my treenodes bold:
Font font = new Font(tvQuestionSequence.Font, FontStyle.Bold);
foreach (QuestionnaireBuilder_Category cat in categories)
{
TreeNode node = new TreeNode();
node.Text = cat.Description;
node.Name = cat.Id.ToString();
node.NodeFont = font;
tvQuestionSequence.Nodes.Add(node);
}
But the text of the bold nodes is not displayed correctly. The last letter(s) are not shown. How come? And how to solve this problem?
Source: (StackOverflow)
I am trying to get a TreeView to bind my collection so that all groups show nested groups and each group will show entry.
How can I use the HierarchicalDataTemplate so that the TreeView will process both SubGroups and Entries collection?
Groups show subgroups and entries:
Example:
Group1
--Entry
--Entry
Group2
--Group4
----Group1
------Entry
------Entry
----Entry
----Entry
--Entry
--Entry
Group3
--Entry
--Entry
Objects:
namespace TaskManager.Domain
{
public class Entry
{
public int Key { get; set; }
public string Name { get; set; }
}
}
namespace TaskManager.Domain
{
public class Group
{
public int Key { get; set; }
public string Name { get; set; }
public IList<Group> SubGroups { get; set; }
public IList<Entry> Entries { get; set; }
}
}
Test data:
namespace DrillDownView
{
public class TestData
{
public IList<Group> Groups = new List<Group>();
public void Load()
{
Group grp1 = new Group() { Key = 1, Name = "Group 1", SubGroups = new List<Group>(), Entries = new List<Entry>() };
Group grp2 = new Group() { Key = 2, Name = "Group 2", SubGroups = new List<Group>(), Entries = new List<Entry>() };
Group grp3 = new Group() { Key = 3, Name = "Group 3", SubGroups = new List<Group>(), Entries = new List<Entry>() };
Group grp4 = new Group() { Key = 4, Name = "Group 4", SubGroups = new List<Group>(), Entries = new List<Entry>() };
//grp1
grp1.Entries.Add(new Entry() { Key=1, Name="Entry number 1" });
grp1.Entries.Add(new Entry() { Key=2, Name="Entry number 2" });
grp1.Entries.Add(new Entry() { Key=3,Name="Entry number 3" });
//grp2
grp2.Entries.Add(new Entry(){ Key=4, Name = "Entry number 4"});
grp2.Entries.Add(new Entry(){ Key=5, Name = "Entry number 5"});
grp2.Entries.Add(new Entry(){ Key=6, Name = "Entry number 6"});
//grp3
grp3.Entries.Add(new Entry(){ Key=7, Name = "Entry number 7"});
grp3.Entries.Add(new Entry(){ Key=8, Name = "Entry number 8"});
grp3.Entries.Add(new Entry(){ Key=9, Name = "Entry number 9"});
//grp4
grp4.Entries.Add(new Entry(){ Key=10, Name = "Entry number 10"});
grp4.Entries.Add(new Entry(){ Key=11, Name = "Entry number 11"});
grp4.Entries.Add(new Entry(){ Key=12, Name = "Entry number 12"});
grp4.SubGroups.Add(grp1);
grp2.SubGroups.Add(grp4);
Groups.Add(grp1);
Groups.Add(grp2);
Groups.Add(grp3);
}
}
}
XAML:
<Window x:Class="DrillDownView.Window2"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:TaskManager.Domain;assembly=TaskManager.Domain"
Title="Window2" Height="300" Width="300">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<TreeView Name="GroupView" Grid.Row="0" Grid.Column="0" ItemsSource="{Binding}">
<TreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type local:Group}" ItemsSource="{Binding SubGroups}">
<TextBlock Text="{Binding Path=Name}" />
</HierarchicalDataTemplate>
<HierarchicalDataTemplate DataType="{x:Type local:Entry}" ItemsSource="{Binding Entries}">
<TextBlock Text="{Binding Path=Name}" />
</HierarchicalDataTemplate>
</TreeView.Resources>
</TreeView>
</Grid>
</Window>
XAML.CS:
public partial class Window2 : Window
{
public Window2()
{
InitializeComponent();
LoadView();
}
private void LoadView()
{
TestData data = new TestData();
data.Load();
GroupView.ItemsSource = data.Groups;
}
}
Source: (StackOverflow)