c# - TreeView with CompositeCollection, expand arrow not showing

Question

I have a TreeView which is bound to CompositeCollection made of MyItem and MyGroup objects.

Class definitions:

public class MyItem
{
    public string Name { get; set; }

    public MyItem(string name = "")
    {
        Name = name;
    }
}


public class MyGroup
{
    public string Name { get; set; }
    public List<MyGroup> MyGroups = new List<MyGroup>();
    public List<MyItem> MyItems = new List<MyItem>();

    public IList Children
    {
        get
        {
            return new CompositeCollection()
            {
                new CollectionContainer { Collection = MyGroups },
                new CollectionContainer { Collection = MyItems }
            };
        }
    }

    public MyGroup(string name)
    {
        Name = name;
    }
}

XAML:

<TreeView Name="myTreeView">
    <TreeView.Resources>
        <HierarchicalDataTemplate DataType="{x:Type local:MyGroup}" ItemsSource="{Binding Children}">
            <TextBlock Text="{Binding Name}" />
        </HierarchicalDataTemplate>
        <HierarchicalDataTemplate DataType="{x:Type local:MyItem}">
            <TextBlock Text="{Binding Name}" />
        </HierarchicalDataTemplate>
    </TreeView.Resources>
</TreeView>

Code for setting up the tree:

var root = new ObservableCollection<MyGroup>();
myTreeView.ItemsSource = root;

MyGroup g1 = new MyGroup("First");
MyGroup g2 = new MyGroup("Second");
MyGroup g3 = new MyGroup("Third");
MyItem i1 = new MyItem("Item1");
MyItem i2 = new MyItem("Item2");
MyItem i3 = new MyItem("Item3");

root.Add(g1);
root.Add(g2);
g2.MyGroups.Add(g3);
g1.MyItems.Add(i1);

The problem is whenever I run the code, only First and Second are displayed, but the expand arrow is not present next to Second, and it can't be expanded. Debugging shows the g2 has g3 as child, but it is not present in the TreeView control.

How can I fix it? The aim is to do it with as little code as possible, I try to avoid adding loads of abstraction layers and wrapper classes...

Went through these, didn't solve my problem:

• WPF Treeview Databinding Hierarchal Data with mixed types

• http://www.codeproject.com/Articles/26288/Simplifying-the-WPF-TreeView-by-Using-the-ViewMode

Answer 1

我能够通过源代码中的以下修改来解决问题：

MyGroup 类：

public class MyGroup
{
    public string Name { get; set; }

    private IList children = new CompositeCollection() {
                new CollectionContainer { Collection = new List<MyGroup>() },
                new CollectionContainer { Collection = new List<TestItem>() }
    };

    public IList Children
    {
        get { return children; }
        set { children = value; }
    }

    public MyGroup(string name)
    {
        Name = name;
    }
}

设置树的代码：

var root = new ObservableCollection<MyGroup>();
myTreeView.ItemsSource = root;

MyGroup g1 = new MyGroup("First");
MyGroup g2 = new MyGroup("Second");
MyGroup g3 = new MyGroup("Third");
MyItem i1 = new MyItem("Item1");
MyItem i2 = new MyItem("Item2");
MyItem i3 = new MyItem("Item3");

root.Add(g1);
root.Add(g2);
g2.Children.Add(g3);
g1.Children.Add(i1);

因此，尽管WPF Treeview Databinding Hierarchal Data with mixed types提出了什么建议，我不得不摆脱 MyGroup 中的两个单独列表（代表不同类型的对象），只使用一个 CompositeCollection，然后添加子项到子列表中，无论子对象的类型如何。