# Class Tree

java.lang.Object
com.codename1.ui.Component
com.codename1.ui.Container
com.codename1.ui.tree.Tree

All Implemented Interfaces:
  `Animation, Editable, StyleListener, Iterable<Component>`

Direct Known Subclasses:
  `FileTree`

public class Tree extends Container

The `Tree` component allows constructing simple tree component hierarchies that can be expanded seamlessly with no limit. The tree is bound to a model that can provide data with free form depth such as file system or similarly structured data.

To customize the look of the tree the component can be derived and component creation can be replaced.

    class StringArrayTreeModel implements TreeModel {
        String[][] arr = new String[][] {
                {"Colors", "Letters", "Numbers"},
                {"Red", "Green", "Blue"},
                {"A", "B", "C"},
                {"1", "2", "3"}
            };

        public Vector getChildren(Object parent) {
            if(parent == null) {
                Vector v = new Vector();
                for(int iter = 0 ; iter  iter + 1 && arr[iter + 1] != null) {
                        for(int i = 0 ; i

    And heres a more "real world" example showing an XML hierarchy in a `Tree`:

    ```java
    class XMLTreeModel implements TreeModel {
    private Element root;
    public XMLTreeModel(Element e) {
    root = e;
    }

    public Vector getChildren(Object parent) {
    if(parent == null) {
    Vector c = new Vector();
    c.addElement(root);
    return c;
    }
    Vector result = new Vector();
    Element e = (Element)parent;
    for(int iter = 0 ; iter

    Another real world example showing the `com.codename1.io.FileSystemStorage` as a tree:

    ```java
    Form hi = new Form("FileSystemTree", new BorderLayout());
    TreeModel tm = new TreeModel() {
    @Override
        public Vector getChildren(Object parent) {
            String[] files;
            if(parent == null) {
                files = FileSystemStorage.getInstance().getRoots();
                return new Vector(Arrays.asList(files));
            } else {
                try {
                    files = FileSystemStorage.getInstance().listFiles((String)parent);
                } catch(IOException err) {
                    Log.e(err);
                    files = new String[0];
                }
            }
            String p = (String)parent;
            Vector result = new Vector();
            for(String s : files) {
                result.add(p + s);
            }
            return result;
        }
    @Override
        public boolean isLeaf(Object node) {
            return !FileSystemStorage.getInstance().isDirectory((String)node);
        }
    };
    Tree t = new Tree(tm) {
    @Override
        protected String childToDisplayLabel(Object child) {
            String n = (String)child;
            int pos = n.lastIndexOf("/");
            if(pos
    @author Shai Almog

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static interface`
  `Tree.TreeState`
  A marker interface used for Tree state returned from `#getTreeState()` and passed to `#setTreeState(com.codename1.ui.tree.Tree.TreeState)` for retaining state in a Tree when the model is changed.

- ## Field Summary

  ### Fields inherited from class Component

  `BASELINE, BOTTOM, BRB_CENTER_OFFSET, BRB_CONSTANT_ASCENT, BRB_CONSTANT_DESCENT, BRB_OTHER, CENTER, CROSSHAIR_CURSOR, DEFAULT_CURSOR, DRAG_REGION_IMMEDIATELY_DRAG_X, DRAG_REGION_IMMEDIATELY_DRAG_XY, DRAG_REGION_IMMEDIATELY_DRAG_Y, DRAG_REGION_LIKELY_DRAG_X, DRAG_REGION_LIKELY_DRAG_XY, DRAG_REGION_LIKELY_DRAG_Y, DRAG_REGION_NOT_DRAGGABLE, DRAG_REGION_POSSIBLE_DRAG_X, DRAG_REGION_POSSIBLE_DRAG_XY, DRAG_REGION_POSSIBLE_DRAG_Y, E_RESIZE_CURSOR, HAND_CURSOR, LEFT, MOVE_CURSOR, N_RESIZE_CURSOR, NE_RESIZE_CURSOR, NW_RESIZE_CURSOR, RIGHT, S_RESIZE_CURSOR, SE_RESIZE_CURSOR, SW_RESIZE_CURSOR, TEXT_CURSOR, TOP, W_RESIZE_CURSOR, WAIT_CURSOR`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `Tree()`
  Constructor for usage by GUI builder and automated tools, normally one should use the version that accepts the model
  `Tree(TreeModel model)`
  Construct a tree with the given tree model

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `addLeafListener(ActionListener l)`
  A listener that fires when a leaf is clicked
  `protected void`
  `bindNodeListener(ActionListener l, Component node)`
  Since a node may be any component type developers should override this method to add support for binding the click listener to the given component.
  `protected Dimension`
  `calcPreferredSize()`
  Calculates the preferred size based on component content.
  `protected String`
  `childToDisplayLabel(Object child)`
  Converts a tree child to a label, this method can be overriden for simple rendering effects
  `void`
  `collapsePath(Object... path)`
  Collapses the last element in the path
  `protected Component`
  `createNode(Object node, int depth)`
  Creates a node within the tree, this method is protected allowing tree to be subclassed to replace the rendering logic of individual tree buttons.
  `protected Button`
  `createNodeComponent(Object node, int depth)`
  Creates a node within the tree, this method is protected allowing tree to be subclassed to replace the rendering logic of individual tree buttons.
  `void`
  `expandPath(boolean animate, Object... path)`
  Expands the tree path
  `void`
  `expandPath(Object... path)`
  Expands the tree path
  `Component`
  `findNodeComponent(Object node)`
  Finds the component for a model node.
  `Component`
  `findNodeComponent(Object node, Component root)`
  Finds the component for a model node.
  `TreeModel`
  `getModel()`
  Returns the tree model instance
  `protected Object`
  `getModel(Component node)`
  Gets the model for a component in the tree.
  `Component`
  `getParentComponent(Component nodeComponent)`
  Gets the UI component corresponding to the parent model mode of the node corresponding with the given UI component.
  `Object`
  `getParentNode(Component nodeComponent)`
  Gets the parent model node for a component.
  `String[]`
  `getPropertyNames()`
  A component may expose mutable property names for a UI designer to manipulate, this API is designed for usage internally by the GUI builder code
  `String[]`
  `getPropertyTypeNames()`
  This method is here to workaround an XMLVM array type bug where property types aren't identified properly, it returns the names of the types using the following type names: String,int,double,long,byte,short,char,String[],String[][],byte[],Image,Image[],Object[],ListModel,ListCellRenderer
  `Class[]`
  `getPropertyTypes()`
  Matches the property names method (see that method for further details).
  `Object`
  `getPropertyValue(String name)`
  Returns the current value of the property name, this method is used by the GUI builder
  `Object`
  `getSelectedItem()`
  Returns the currently selected item in the tree
  `Tree.TreeState`
  `getTreeState()`
  Gets the state of the tree in a format that can be restored later by either the same tree or a different tree whose model includes the same nodes.
  `protected boolean`
  `isExpanded(Component node)`
  This method returns true if the given node is expanded.
  `boolean`
  `isMultilineMode()`
  Toggles a mode where rows in the tree can be broken since span buttons will be used instead of plain buttons.
  `void`
  `refreshNode(Component nodeComponent)`
  Refreshes a node of the tree.
  `void`
  `removeLeafListener(ActionListener l)`
  Removes the listener that fires when a leaf is clicked
  `static void`
  `setFolderIcon(Image folderIcon)`
  Sets the icon for a tree folder
  `static void`
  `setFolderOpenIcon(Image folderIcon)`
  Sets the icon for a tree folder in its expanded state
  `void`
  `setModel(TreeModel model)`
  Sets the tree model to a new value
  `void`
  `setMultilineMode(boolean multilineMode)`
  Toggles a mode where rows in the tree can be broken since span buttons will be used instead of plain buttons.
  `static void`
  `setNodeIcon(Image nodeIcon)`
  Sets the icon for a tree node
  `protected void`
  `setNodeIcon(Image icon, Component node)`
  Sets the icon for the given node similar in scope to bindNodeListener
  `protected void`
  `setNodeMaterialIcon(char c, Component node, float size)`
  Sets material icon for the node.
  `String`
  `setPropertyValue(String name, Object value)`
  Sets a new value to the given property, returns an error message if failed and null if successful.
  `void`
  `setTreeState(Tree.TreeState state)`
  Sets the tree state.

  ### Methods inherited from class Container

  `add, add, add, add, add, add, addAll, addComponent, addComponent, addComponent, addComponent, animateHierarchy, animateHierarchyAndWait, animateHierarchyFade, animateHierarchyFadeAndWait, animateLayout, animateLayoutAndWait, animateLayoutFade, animateLayoutFadeAndWait, animateUnlayout, animateUnlayoutAndWait, applyRTL, cancelRepaints, clearClientProperties, constrainHeightWhenScrollable, constrainWidthWhenScrollable, contains, createAnimateHierarchy, createAnimateHierarchyFade, createAnimateLayout, createAnimateLayoutFade, createAnimateLayoutFadeAndWait, createAnimateMotion, createAnimateUnlayout, createReplaceTransition, dragInitiated, drop, encloseIn, encloseIn, findDropTargetAt, findFirstFocusable, fireClicked, flushReplace, forceRevalidate, getBottomGap, getChildrenAsList, getClosestComponentTo, getComponentAt, getComponentAt, getComponentCount, getComponentIndex, getGridPosX, getGridPosY, getLayout, getLayoutHeight, getLayoutWidth, getLeadComponent, getLeadParent, getResponderAt, getSafeAreaRoot, getScrollIncrement, getSideGap, getUIManager, initLaf, invalidate, isEnabled, isSafeArea, isSafeAreaRoot, isScrollableX, isScrollableY, isSelectableInteraction, isSurface, iterator, iterator, keyPressed, keyReleased, layoutContainer, morph, morphAndWait, paint, paintComponentBackground, paintGlass, paramString, pointerPressed, refreshTheme, removeAll, removeComponent, replace, replace, replaceAndWait, replaceAndWait, replaceAndWait, revalidate, revalidateLater, revalidateWithAnimationSafety, scrollComponentToVisible, setCellRenderer, setEnabled, setLayout, setLeadComponent, setSafeArea, setSafeAreaRoot, setScrollable, setScrollableX, setScrollableY, setScrollIncrement, setShouldCalcPreferredSize, setShouldLayout, setUIManager, updateTabIndices`

  ### Methods inherited from class Component

  `addDragFinishedListener, addDragOverListener, addDropListener, addFocusListener, addLongPressListener, addPointerDraggedListener, addPointerPressedListener, addPointerReleasedListener, addPullToRefresh, addScrollListener, addStateChangeListener, animate, announceForAccessibility, bindProperty, blocksSideSwipe, calcScrollSize, contains, containsOrOwns, createStyleAnimation, deinitialize, deinitializeCustomStyle, dragEnter, dragExit, dragFinished, draggingOver, drawDraggedImage, focusGained, focusLost, getAbsoluteX, getAbsoluteY, getAccessibilityText, getAllStyles, getAnimationManager, getBaseline, getBaselineResizeBehavior, getBindablePropertyNames, getBindablePropertyTypes, getBorder, getBoundPropertyValue, getBounds, getBounds, getClientProperty, getCloudBoundProperty, getCloudDestinationProperty, getComponentForm, getComponentState, getCursor, getDefaultDragTransparency, getDirtyRegion, getDisabledStyle, getDraggedx, getDraggedy, getDragImage, getDragRegionStatus, getDragSpeed, getDragTransparency, getEditingDelegate, getHeight, getInlineAllStyles, getInlineDisabledStyles, getInlinePressedStyles, getInlineSelectedStyles, getInlineStylesTheme, getInlineUnselectedStyles, getInnerHeight, getInnerPreferredH, getInnerPreferredW, getInnerWidth, getInnerX, getInnerY, getLabelForComponent, getName, getNativeOverlay, getNextFocusDown, getNextFocusLeft, getNextFocusRight, getNextFocusUp, getOuterHeight, getOuterPreferredH, getOuterPreferredW, getOuterWidth, getOuterX, getOuterY, getOwner, getParent, getPreferredH, getPreferredSize, getPreferredSizeStr, getPreferredTabIndex, getPreferredW, getPressedStyle, getSameHeight, getSameWidth, getScrollable, getScrollAnimationSpeed, getScrollDimension, getScrollOpacity, getScrollOpacityChangeSpeed, getScrollX, getScrollY, getSelectCommandText, getSelectedRect, getSelectedStyle, getStyle, getTabIndex, getTensileLength, getTextSelectionSupport, getTooltip, getUIID, getUnselectedStyle, getVisibleBounds, getVisibleBounds, getWidth, getX, getY, growShrink, handlesInput, hasFixedPreferredSize, hasFocus, hideNativeOverlay, initComponent, initCustomStyle, initDisabledStyle, initPressedStyle, initSelectedStyle, initUnselectedStyle, installDefaultPainter, isAlwaysTensile, isBlockLead, isCellRenderer, isChildOf, isDragActivated, isDragAndDropOperation, isDraggable, isDragRegion, isDropTarget, isEditable, isEditing, isFlatten, isFocusable, isGrabsPointerEvents, isHidden, isHidden, isHideInLandscape, isHideInPortrait, isIgnorePointerEvents, isInClippingRegion, isInitialized, isOpaque, isOwnedBy, isPinchBlocksDragAndDrop, isRippleEffect, isRTL, isScrollable, isScrollVisible, isSetCursorSupported, isSmoothScrolling, isSnapToGrid, isStickyDrag, isTactileTouch, isTactileTouch, isTensileDragEnabled, isTraversable, isVisible, keyRepeated, laidOut, longKeyPress, longPointerPress, onScrollX, onScrollY, onSetFocusable, paintBackground, paintBackgrounds, paintBorder, paintBorderBackground, paintComponent, paintComponent, paintIntersectingComponentsAbove, paintLock, paintLockRelease, paintRippleOverlay, paintScrollbars, paintScrollbarX, paintScrollbarY, paintShadows, parsePreferredSize, pinch, pinch, pinchReleased, pointerDragged, pointerDragged, pointerHover, pointerHoverPressed, pointerHoverReleased, pointerPressed, pointerReleased, pointerReleased, putClientProperty, refreshTheme, refreshTheme, remove, removeDragFinishedListener, removeDragOverListener, removeDropListener, removeFocusListener, removeLongPressListener, removePointerDraggedListener, removePointerPressedListener, removePointerReleasedListener, removeScrollListener, removeStateChangeListener, repaint, repaint, requestFocus, resetFocusable, respondsToPointerEvents, scrollRectToVisible, scrollRectToVisible, setAccessibilityText, setAlwaysTensile, setBlockLead, setBoundPropertyValue, setCloudBoundProperty, setCloudDestinationProperty, setComponentState, setCursor, setDefaultDragTransparency, setDirtyRegion, setDisabledStyle, setDraggable, setDragTransparency, setDropTarget, setEditingDelegate, setFlatten, setFocus, setFocusable, setGrabsPointerEvents, setHandlesInput, setHeight, setHidden, setHidden, setHideInLandscape, setHideInPortrait, setIgnorePointerEvents, setInitialized, setInlineAllStyles, setInlineDisabledStyles, setInlinePressedStyles, setInlineSelectedStyles, setInlineStylesTheme, setInlineUnselectedStyles, setIsScrollVisible, setLabelForComponent, setName, setNextFocusDown, setNextFocusLeft, setNextFocusRight, setNextFocusUp, setOpaque, setOwner, setPinchBlocksDragAndDrop, setPreferredH, setPreferredSize, setPreferredSizeStr, setPreferredTabIndex, setPreferredW, setPressedStyle, setRippleEffect, setRTL, setSameHeight, setSameSize, setSameWidth, setScrollAnimationSpeed, setScrollOpacityChangeSpeed, setScrollSize, setScrollVisible, setScrollX, setScrollY, setSelectCommandText, setSelectedStyle, setSize, setSmoothScrolling, setSnapToGrid, setTabIndex, setTactileTouch, setTensileDragEnabled, setTensileLength, setTooltip, setTraversable, setUIID, setUIID, setUIIDFinal, setUnselectedStyle, setVisible, setWidth, setX, setY, shouldBlockSideSwipe, shouldBlockSideSwipeLeft, shouldBlockSideSwipeRight, shouldRenderComponentSelection, showNativeOverlay, startEditingAsync, stopEditing, stripMarginAndPadding, styleChanged, toImage, toString, unbindProperty, updateNativeOverlay, visibleBoundsContains`

  ### Methods inherited from class Object

  `clone, equals, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- ## Constructor Details

  - ### Tree

    public Tree()
    Constructor for usage by GUI builder and automated tools, normally one should use the version that accepts the model

  - ### Tree

    public Tree(TreeModel model)

    Construct a tree with the given tree model

    ###### Parameters

    - `model`: represents the contents of the tree

- ## Method Details

  - ### setFolderIcon

    public static void setFolderIcon(Image folderIcon)

    Sets the icon for a tree folder

    ###### Parameters

    - `folderIcon`: the icon for a folder within the tree

  - ### setFolderOpenIcon

    public static void setFolderOpenIcon(Image folderIcon)

    Sets the icon for a tree folder in its expanded state

    ###### Parameters

    - `folderIcon`: the icon for a folder within the tree

  - ### setNodeIcon

    public static void setNodeIcon(Image nodeIcon)

    Sets the icon for a tree node

    ###### Parameters

    - `nodeIcon`: the icon for a node within the tree

  - ### getTreeState

    public Tree.TreeState getTreeState()

    Gets the state of the tree in a format that can be restored later by either the same tree or a different tree whose model includes the same nodes.

    ###### Returns

    A TreeState object that can be passed to `#setTreeState(com.codename1.ui.tree.Tree.TreeState)`

  - ### setTreeState

    public void setTreeState(Tree.TreeState state)

    Sets the tree state.

    ###### Parameters

    - `state`: The state, which was returned from the `#getTreeState()` method.

  - ### isMultilineMode

    public boolean isMultilineMode()

    Toggles a mode where rows in the tree can be broken since span buttons will be used instead of plain buttons.

    ###### Returns

    the multilineMode

  - ### setMultilineMode

    public void setMultilineMode(boolean multilineMode)

    Toggles a mode where rows in the tree can be broken since span buttons will be used instead of plain buttons.

    ###### Parameters

    - `multilineMode`: the multilineMode to set

  - ### getPropertyNames

    public String[] getPropertyNames()

    A component may expose mutable property names for a UI designer to manipulate, this API is designed for usage internally by the GUI builder code

    ###### Returns

    the property names allowing mutation

    Overrides:
      `getPropertyNames` in class `Component`

  - ### getPropertyTypes

    public Class[] getPropertyTypes()

    Matches the property names method (see that method for further details).

    ###### Returns

    the types of the properties

    Overrides:
      `getPropertyTypes` in class `Component`

  - ### getPropertyTypeNames

    public String[] getPropertyTypeNames()

    This method is here to workaround an XMLVM array type bug where property types aren't identified properly, it returns the names of the types using the following type names: String,int,double,long,byte,short,char,String[],String[][],byte[],Image,Image[],Object[],ListModel,ListCellRenderer

    ###### Returns

    Array of type names

    Overrides:
      `getPropertyTypeNames` in class `Component`

  - ### getPropertyValue

    public Object getPropertyValue(String name)

    Returns the current value of the property name, this method is used by the GUI builder

    ###### Parameters

    - `name`: the name of the property

    ###### Returns

    the value of said property

    Overrides:
      `getPropertyValue` in class `Component`

  - ### setPropertyValue

    public String setPropertyValue(String name, Object value)

    Sets a new value to the given property, returns an error message if failed and null if successful. Notice that some builtin properties such as "$designMode" might be sent to components to indicate application state.

    ###### Parameters

    - `name`: the name of the property

    - `value`: new value for the property

    ###### Returns

    error message or null

    Overrides:
      `setPropertyValue` in class `Component`

  - ### getModel

    public TreeModel getModel()

    Returns the tree model instance

    ###### Returns

    the tree model

  - ### setModel

    public void setModel(TreeModel model)

    Sets the tree model to a new value

    ###### Parameters

    - `model`: the model of the tree

  - ### isExpanded

    protected boolean isExpanded(Component node)

    This method returns true if the given node is expanded.

    ###### Parameters

    - `node`: a Component that represents a tree node.

    ###### Returns

    true if this tree node is expanded

  - ### findNodeComponent

    public Component findNodeComponent(Object node)

    Finds the component for a model node.

    ###### Parameters

    - `node`: The node from the model.

    ###### Returns

    The corresponding component in the UI or null if not found.

    ###### Since

    7.0

  - ### findNodeComponent

    public Component findNodeComponent(Object node, Component root)

    Finds the component for a model node.

    ###### Parameters

    - `node`: Model node whose view we seek.

    - `root`: A root component - we check root and its descendents.

    ###### Returns

    The corresponding UI component for node, or null if not found.

    ###### Since

    7.0

  - ### expandPath

    public void expandPath(Object... path)

    Expands the tree path

    ###### Parameters

    - `path`: the path to expand

  - ### expandPath

    public void expandPath(boolean animate, Object... path)

    Expands the tree path

    ###### Parameters

    - `path`: the path to expand

    - `animate`: whether to animate expansion

  - ### collapsePath

    public void collapsePath(Object... path)

    Collapses the last element in the path

    ###### Parameters

    - `path`: the path to the element that should be collapsed

  - ### getSelectedItem

    public Object getSelectedItem()

    Returns the currently selected item in the tree

    ###### Returns

    the object selected within the tree

  - ### getParentNode

    public Object getParentNode(Component nodeComponent)

    Gets the parent model node for a component.

    ###### Parameters

    - `nodeComponent`: The UI for a node.

    ###### Returns

    The model node's parent, or null if not found.

  - ### getParentComponent

    public Component getParentComponent(Component nodeComponent)

    Gets the UI component corresponding to the parent model mode of the node corresponding with the given UI component.

    ###### Parameters

    - `nodeComponent`: UI component, whose node we seek the parent.

    ###### Returns

    UI component for the given node's parent.

    ###### Since

    7.0

  - ### refreshNode

    public void refreshNode(Component nodeComponent)

    Refreshes a node of the tree.

    ###### Parameters

    - `nodeComponent`: The node component.

    ###### Since

    7.0

  - ### createNodeComponent

    protected Button createNodeComponent(Object node, int depth)

    Creates a node within the tree, this method is protected allowing tree to be subclassed to replace the rendering logic of individual tree buttons.

    ###### Parameters

    - `node`: the node object from the model to display on the button

    - `depth`: the depth within the tree (normally represented by indenting the entry)

    ###### Returns

    a button representing the node within the tree

    ###### Deprecated

    replaced with createNode, bindNodeListener and setNodeIcon

  - ### bindNodeListener

    protected void bindNodeListener(ActionListener l, Component node)

    Since a node may be any component type developers should override this method to add support for binding the click listener to the given component.

    ###### Parameters

    - `l`: listener interface

    - `node`: node component returned by createNode

  - ### setNodeIcon

    protected void setNodeIcon(Image icon, Component node)

    Sets the icon for the given node similar in scope to bindNodeListener

    ###### Parameters

    - `icon`: the icon for the node

    - `node`: the node instance

  - ### setNodeMaterialIcon

    protected void setNodeMaterialIcon(char c, Component node, float size)

    Sets material icon for the node.

    ###### Parameters

    - `c`: Material icon code. See `FontImage`

    - `node`: The node to set the icon for.

    - `size`: The size in millimetres for the icon.

    ###### Since

    7.0

  - ### createNode

    protected Component createNode(Object node, int depth)

    Creates a node within the tree, this method is protected allowing tree to be subclassed to replace the rendering logic of individual tree buttons.

    ###### Parameters

    - `node`: the node object from the model to display on the button

    - `depth`: the depth within the tree (normally represented by indenting the entry)

    ###### Returns

    a button representing the node within the tree

  - ### childToDisplayLabel

    protected String childToDisplayLabel(Object child)

    Converts a tree child to a label, this method can be overriden for simple rendering effects

    ###### Returns

    a string representing the given tree node

  - ### addLeafListener

    public void addLeafListener(ActionListener l)

    A listener that fires when a leaf is clicked

    ###### Parameters

    - `l`: listener to fire when the leaf is clicked

  - ### removeLeafListener

    public void removeLeafListener(ActionListener l)

    Removes the listener that fires when a leaf is clicked

    ###### Parameters

    - `l`: listener to remove

  - ### getModel

    protected Object getModel(Component node)

    Gets the model for a component in the tree.

    ###### Parameters

    - `node`: The component whose model we want to obtain.

    ###### Returns

    The model.

    ###### Since

    7.0

  - ### calcPreferredSize

    protected Dimension calcPreferredSize()

    Calculates the preferred size based on component content. This method is invoked lazily by getPreferred size.

    ###### Returns

    the calculated preferred size based on component content

    Overrides:
      `calcPreferredSize` in class `Container`