System.invalidoperationexception: 'items collection must be empty before using itemssource.'

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When I click on the button system throws exception

System.InvalidOperationException: 'Items collection must be empty before using ItemsSource.'

I am unable to find the problem

What I have tried:

I am trying to create a tree when click on a button like this

C#

<pre>private void Button_Click_1(object sender, RoutedEventArgs e)
        {
            var subModules = new List<ITreeNode>
        {
            new SubModule { Name = "Sub Module 1" }
        };
            var subThreads = new List<ITreeNode>
        {
            new SubThread { Name = "Sub Thread 1" }
        };
            var nodes = new List<ITreeNode>
        {
            new Thread { Name = "Thread ", ChildNodes = subThreads },
            new Module { Name = "Module ", ChildNodes = subModules }
        };
            var processes = new List<RunProcesses>
        {
            new RunProcesses{ Name = "Process1", ChildNodes = nodes }
        };
            TreeView.ItemsSource = processes;

        }

Posted 10-Jun-18 2:22am

Member 13688663

Updated 10-Jun-18 2:36am

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OriginalGriff · Answer 1 · 2018-06-10T02:38:00

Solution 1

Read the error message, it's pretty explicit:

System.InvalidOperationException: 'Items collection must be empty before using ItemsSource.'

You are setting the ItemsSource property of a collection (the Treeview) which already has data in it.

Check your XAML, or empty the Items Collection.

Posted 10-Jun-18 2:38am

OriginalGriff

Comments

Member 13688663 10-Jun-18 8:59am

<TreeView x:Name="TreeView">
        <treeview.resources>
            <HierarchicalDataTemplate DataType="{x:Type local:RunProcesses}" ItemsSource="{Binding ChildNodes}">
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="{Binding Path=Name, StringFormat='{}{0} '}" />
                    <TextBlock Text="{Binding Path=ID, StringFormat=(ID: {0})}" />
                
            
            <HierarchicalDataTemplate DataType="{x:Type local:Module}" ItemsSource="{Binding ChildNodes}">
                <TextBlock Text="{Binding Path=Name}" />
            

            <HierarchicalDataTemplate DataType="{x:Type local:Thread}" ItemsSource="{Binding ChildNodes}">
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="{Binding Path=Name, StringFormat='{}{0} '}" />
                    <TextBlock Text="{Binding Path=ID, StringFormat=(ID: {0})}" />
                
            
            <HierarchicalDataTemplate DataType="{x:Type local:SubThread}" ItemsSource="{Binding ChildNodes}">
                <TextBlock Text="{Binding Path=Name}" />

This is xmal code and itemsource is empty

Member 13688663 10-Jun-18 9:00am

These are classes
public interface ITreeNode
{
string Name { get; set; }
List<itreenode> ChildNodes { get; set; }
}
public class RunProcesses : ITreeNode
{
public string Name { get; set; }
public int ID { get; set; }
public List<itreenode> ChildNodes { get; set; }
}
public class Module : ITreeNode
{
public string Name { get; set; }
public List<itreenode> ChildNodes { get; set; }
}
public class Thread : ITreeNode
{
public string Name { get; set; }
public int ID { get; set; }
public List<itreenode> ChildNodes { get; set; }
}
public class SubModule : ITreeNode
{
public string Name { get; set; }
public List<itreenode> ChildNodes { get => null; set => throw new System.NotImplementedException(); }
}
public class SubThread : ITreeNode
{
public string Name { get; set; }
public List<itreenode> ChildNodes { get => null; set => throw new System.NotImplementedException(); }
}

Member 13688663 10-Jun-18 9:02am

Kindly guide me where I am wrong