Table of Contents

Class NodeTreeModel<T>

Namespace
Qt.Bridge.Models
Assembly
Qt.Bridge.CSharp.Api.dll

Provides a strongly typed base class for adapting an existing single-column tree.

public abstract class NodeTreeModel<T> : TreeModel where T : class

Type Parameters

T

The reference type used for tree nodes.

Inheritance
NodeTreeModel<T>
Derived
Inherited Members

Remarks

Derive from NodeTreeModel<T> when each item in a hierarchy is represented by a node object. Implement the root and child lookup members to describe the tree, and implement ParentOf(T) and IndexOf(T) so the model can navigate from an item back to its parent.

The base class assigns each node a stable internal model id using reference identity. A node must therefore occur at most once in the tree and must remain the same object while it is exposed by the model. Report structural changes with the protected begin/end helpers before and after changing the backing tree, so connected views can update correctly.

T is constrained to a reference type because a tree index must identify one stable node object, and null represents the absence of a parent for root nodes. Value types do not provide either convention reliably when copied or boxed.

Single-column means that each node provides one displayed item or value; it does not limit the depth of the hierarchy. Use a multi-column tree when each node needs sibling values, such as a file name, size, and modified date.

Public instance properties on T are exposed automatically as named values, called roles, that are available to QML. IDisplayable, IEditable, and IModelItem provide the same display, editing, and flag conventions as ListModel<T> and TableModel<T>.

important

This model exposes exactly one column for each node. For a hierarchical model with multiple columns, derive from the non-generic TreeModel and implement its index, parent, column, and value lookup behavior for the application's data structure. 

public sealed class FolderNode(string name)
{
    public string Name { get; } = name;
    public FolderNode Parent { get; private set; }
    public List<FolderNode> Children { get; } = [];

    public FolderNode Add(FolderNode child)
    {
        child.Parent = this;
        Children.Add(child);
        return this;
    }
}

public sealed class FolderTree : NodeTreeModel<FolderNode>
{
    private readonly List<FolderNode> roots =
    [
        new FolderNode("Projects")
            .Add(new FolderNode("Qt"))
            .Add(new FolderNode("CSharp"))
    ];

    protected override int RootCount => roots.Count;
    protected override FolderNode RootAt(int row) => roots[row];
    protected override int ChildCount(FolderNode parent) => parent.Children.Count;
    protected override FolderNode ChildAt(FolderNode parent, int row) =>
        parent.Children[row];
    protected override FolderNode ParentOf(FolderNode node) => node.Parent;
    protected override int IndexOf(FolderNode node) =>
        node.Parent is null ? roots.IndexOf(node) : node.Parent.Children.IndexOf(node);
}

Properties

HasItemRole

Gets whether the complete node is exposed through the item role.

protected virtual bool HasItemRole { get; }

Property Value

bool

IsReadOnly

Gets whether the model should reject all edit operations.

protected virtual bool IsReadOnly { get; }

Property Value

bool

RoleProperties

Gets the public node properties exposed as automatic QML roles.

protected virtual IEnumerable<PropertyInfo> RoleProperties { get; }

Property Value

IEnumerable<PropertyInfo>

RootCount

Gets the number of root-level nodes.

protected abstract int RootCount { get; }

Property Value

int

Methods

ChildAt(T, int)

Returns the child of parent at row.

protected abstract T ChildAt(T parent, int row)

Parameters

parent T
row int

Returns

T

ChildCount(T)

Returns the number of children of parent.

protected abstract int ChildCount(T parent)

Parameters

parent T

Returns

int

ClearItemData(ModelIndex)

Clears all values associated with the specified item.

public override sealed bool ClearItemData(ModelIndex index)

Parameters

index ModelIndex

Returns

bool

ClearNodeData(T)

Clears the value associated with node.

protected virtual bool ClearNodeData(T node)

Parameters

node T

Returns

bool

ColumnCount(ModelIndex)

Returns the number of columns for the specified parent index.

public override sealed int ColumnCount(ModelIndex parent)

Parameters

parent ModelIndex

Returns

int

Data(ModelIndex, int)

Returns the value stored for the specified item and role.

public override sealed object Data(ModelIndex index, int role)

Parameters

index ModelIndex
role int

Returns

object

DataChanged(T)

Notifies that the data for node changed.

protected void DataChanged(T node)

Parameters

node T

Flags(ModelIndex)

Returns the capability flags for the specified item.

public override sealed int Flags(ModelIndex index)

Parameters

index ModelIndex

Returns

int

Remarks

The default implementation marks items as enabled and selectable.

HasChildren(ModelIndex)

Returns whether the specified parent item has any children.

public override sealed bool HasChildren(ModelIndex parent)

Parameters

parent ModelIndex

Returns

bool

Index(int, int, ModelIndex)

Creates an index that identifies the item at the specified row and column under a parent.

public override sealed ModelIndex Index(int row, int column, ModelIndex parent)

Parameters

row int
column int
parent ModelIndex

Returns

ModelIndex

IndexOf(T)

Returns the current row of node under its parent.

protected abstract int IndexOf(T node)

Parameters

node T

Returns

int

Parent(ModelIndex)

Returns the parent index for the specified item.

public override sealed ModelIndex Parent(ModelIndex index)

Parameters

index ModelIndex

Returns

ModelIndex

ParentOf(T)

Returns the parent of node, or null for a root node.

protected abstract T ParentOf(T node)

Parameters

node T

Returns

T

RoleNames()

Returns the names used to address values exposed by this model.

public override sealed Dictionary<int, string> RoleNames()

Returns

Dictionary<int, string>

Remarks

A role identifies a value that can be requested from an item, such as a display string, an editable value, or a custom property. Return a dictionary whose keys are role ids, such as DisplayRole or values starting at UserRole, and whose values are stable, consumer-facing role names.

RootAt(int)

Returns the root-level node at row.

protected abstract T RootAt(int row)

Parameters

row int

Returns

T

RowCount(ModelIndex)

Returns the number of child rows under the specified parent index.

public override sealed int RowCount(ModelIndex parent)

Parameters

parent ModelIndex

Returns

int

SetData(ModelIndex, object, int)

Updates the value stored for the specified item and role.

public override sealed bool SetData(ModelIndex index, object value, int role)

Parameters

index ModelIndex
value object
role int

Returns

bool

Remarks

Call DataChanged(ModelIndex, ModelIndex, int[]) after a successful in-place edit so that connected consumers refresh the affected data.

SetNode(T, int, T)

Replaces the node at the specified row under parent.

protected virtual bool SetNode(T parent, int row, T value)

Parameters

parent T
row int
value T

Returns

bool

Sibling(int, int, ModelIndex)

Returns another item with the same parent as the specified item.

public override sealed ModelIndex Sibling(int row, int column, ModelIndex index)

Parameters

row int
column int
index ModelIndex

Returns

ModelIndex

TryCreateIndex(T, out ModelIndex)

Creates an index for an existing node.

protected bool TryCreateIndex(T node, out ModelIndex index)

Parameters

node T
index ModelIndex

Returns

bool