When it comes to cursors RadDiagram works with the static DiagramCursors class that contains properties of type Cursor. As you noticed each tool expose a Cursor property, which is set to a property of the DiagramCursors class. Which means that if you replace the value (for example) of the DiagramCursors.Path property, the Cursor of the PathTool will be also changed. However, by design the TextTool does not need a special cursor and this is why it uses the default one for the application (the default arrow icon).
// or whatever cursor you like
To achieve your requirement you can change the cursor manually when the ActiveTool of the diagram is changed. For example when you set the ActiveTool to be a TextTool you can also set the Cursor property of the diagram. Then when the ActiveTool is changed back to PointerTool you can set the cursor back to the default pointer cursor.
//change active tool
.diagram.ActiveTool = MouseTool.PanTool;
.diagram.Cursor = DiagramCursors.Panning;
//change the active back to pointer
.diagram.ActiveTool = MouseTool.PointerTool;
.diagram.Cursor = DiagramCursors.Pointer;
Please let me know if this helps.
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