Create a field to display a tree view

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Use a tree view to display objects, such as a folder structure, in a hierarchical manner. A TreeField contains nodes. The highest node is the root node. A node in the tree can have child nodes under it. A node that has a child is a parent node.

Import the required classes and interfaces.

import net.rim.device.api.ui.component.TreeField;
import net.rim.device.api.ui.component.TreeFieldCallback;
import net.rim.device.api.ui.container.MainScreen;
import java.lang.String;

Implement the TreeFieldCallback interface.

Invoke TreeField.setExpanded() on the TreeField object to specify whether a folder is collapsible. Create a TreeField object and multiple child nodes to the TreeField object. Invoke TreeField.setExpanded() using node4 as a parameter to collapse the folder.

String fieldOne =  new String("Main folder");
...
TreeCallback myCallback = new TreeCallback();
TreeField myTree = new TreeField(myCallback, Field.FOCUSABLE);
int node1 = myTree.addChildNode(0, fieldOne);
int node2 = myTree.addChildNode(0, fieldTwo);
int node3 = myTree.addChildNode(node2, fieldThree);
int node4 = myTree.addChildNode(node3, fieldFour);
...
int node10 = myTree.addChildNode(node1, fieldTen);
myTree.setExpanded(node4, false);
...
mainScreen.add(myTree);

To repaint a TreeField when a node changes, create a class that implements the TreeFieldCallback interface and implement the TreeFieldCallback.drawTreeItem method. The TreeFieldCallback.drawTreeItem method uses the cookie for a tree node to draw a String in the location of a node. The TreeFieldCallback.drawTreeItem method invokes Graphics.drawText() to draw the String.
```
private class TreeCallback implements TreeFieldCallback 
{
    public void drawTreeItem(TreeField _tree, Graphics g, int node, int y, int width, int indent) 
    {
        String text = (String)_tree.getCookie(node); 
        g.drawText(text, indent, y);
    }
}
```

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Create a field to display a tree view