com.google.gwt.user.client.ui

## Class LayoutPanel

- java.lang.Object
- - com.google.gwt.user.client.ui.UIObject
  - - com.google.gwt.user.client.ui.Widget
    - - com.google.gwt.user.client.ui.Panel
      - - com.google.gwt.user.client.ui.ComplexPanel
        - - com.google.gwt.user.client.ui.LayoutPanel

All Implemented Interfaces:
  HasAttachHandlers, HasHandlers, EventListener, AnimatedLayout, HasVisibility, HasWidgets, HasWidgets.ForIsWidget, IndexedPanel, IndexedPanel.ForIsWidget, IsWidget, ProvidesResize, RequiresResize, java.lang.Iterable<Widget>

Direct Known Subclasses:
  RootLayoutPanel

    public class LayoutPanel
    extends ComplexPanel
    implements AnimatedLayout, RequiresResize, ProvidesResize

A panel that lays its children out in arbitrary `layers` using the `Layout` class.

This widget will only work in standards mode, which requires that the HTML page in which it is run have an explicit <!DOCTYPE> declaration.

### Example

>     public class LayoutPanelExample implements EntryPoint {

>       public void onModuleLoad() {
>         // Attach two child widgets to a LayoutPanel, laying them out horizontally,
>         // splitting at 50%.
>         Widget childOne = new HTML("left"), childTwo = new HTML("right");
>         LayoutPanel p = new LayoutPanel();
>         p.add(childOne);
>         p.add(childTwo);

>         p.setWidgetLeftWidth(childOne, 0, PCT, 50, PCT);
>         p.setWidgetRightWidth(childTwo, 0, PCT, 50, PCT);

>         // Attach the LayoutPanel to the RootLayoutPanel. The latter will listen for
>         // resize events on the window to ensure that its children are informed of
>         // possible size changes.
>         RootLayoutPanel rp = RootLayoutPanel.get();
>         rp.add(p);
>       }
>     }

### Use in UiBinder Templates

LayoutPanel elements in `UiBinder` templates lay out their children with arbitrary constraints, using <g:layer> elements. Each layer may have any of the following constraint attributes specified as CSS length attributes: `left`, `top`, `right`, `bottom`, `width` , and `height`.

Precisely zero or two constraints are required for each axis (horizontal and vertical). Specifying no constraints implies that the child should fill that axis completely.

The valid sets of horizontal constraints are:

(none)
  Fill the parent's horizontal axis
left, width
  Fixed width, positioned from parent's left edge
right, width
  Fixed width, positioned from parent's right edge
left, right
  Width implied by fixed distance from parent's left and right edges

The valid sets of vertical constraints are:

(none)
  Fill the parent's vertical axis
top, height
  Fixed height, positioned from parent's top edge
bottom, height
  Fixed height, positioned from parent's bottom edge
top, bottom
  Height implied by fixed distance from parent's top and bottom edges

The values of constraint attributes can be any valid CSS length, such as `1px`, `3em`, or `0` (zero lengths require no units).

For example:

     <g:LayoutPanel>
       <!-- No constraints causes the layer to fill the parent -->
       <g:layer>
         <g:Label>Lorem ipsum...</g:Label>
       </g:layer>
       <!-- Position horizontally 25% from each edge;
            Vertically 4px from the top and 10em tall. -->
       <g:layer left='25%' right='25%' top='4px' height='10em'>
         <g:Label>Header</g:Label>
       </g:layer>
     </g:LayoutPanel>

### Nested Class Summary

### Nested classes/interfaces inherited from class com.google.gwt.user.client.ui.UIObject

`UIObject.DebugIdImpl, UIObject.DebugIdImplEnabled`

### Nested classes/interfaces inherited from interface com.google.gwt.user.client.ui.IndexedPanel

`IndexedPanel.ForIsWidget`

### Nested classes/interfaces inherited from interface com.google.gwt.user.client.ui.HasWidgets

`HasWidgets.ForIsWidget`

### Field Summary

### Fields inherited from class com.google.gwt.user.client.ui.Widget

`eventsToSink`

### Fields inherited from class com.google.gwt.user.client.ui.UIObject

`DEBUG_ID_PREFIX, MISSING_ELEMENT_ERROR, SETELEMENT_TWICE_ERROR`

### Constructor Summary

Constructors
Constructor and Description
`LayoutPanel()` Creates an empty layout panel.

### Method Summary

All Methods Instance Methods Concrete Methods
`void` `add(Widget widget)` Adds a widget to this panel.
`void` `animate(int duration)` Layout children, animating over the specified period of time.
`void` `animate(int duration, Layout.AnimationCallback callback)` Layout children, animating over the specified period of time.
`void` `forceLayout()` Layout children immediately.
`(package private) Layout` `getLayout()` Gets the `Layout` instance associated with this widget.
`Element` `getWidgetContainerElement(Widget child)` Gets the container element wrapping the given child widget.
`void` `insert(Widget widget, int beforeIndex)` Inserts a widget before the specified index.
`protected void` `onAttach()` This method is called when a widget is attached to the browser's document.
`protected void` `onDetach()` This method is called when a widget is detached from the browser's document.
`void` `onResize()` This method must be called whenever the implementor's size has been modified.
`boolean` `remove(Widget w)` Removes a child widget.
`void` `setWidgetBottomHeight(IsWidget child, double bottom, Style.Unit bottomUnit, double height, Style.Unit heightUnit)` Overloaded version for IsWidget.
`void` `setWidgetBottomHeight(Widget child, double bottom, Style.Unit bottomUnit, double height, Style.Unit heightUnit)` Sets the child widget's bottom and height values.
`void` `setWidgetHorizontalPosition(Widget child, Layout.Alignment position)` Sets the child widget's horizontal position within its layer.
`void` `setWidgetLeftRight(IsWidget child, double left, Style.Unit leftUnit, double right, Style.Unit rightUnit)` Overloaded version for IsWidget.
`void` `setWidgetLeftRight(Widget child, double left, Style.Unit leftUnit, double right, Style.Unit rightUnit)` Sets the child widget's left and right values.
`void` `setWidgetLeftWidth(IsWidget child, double left, Style.Unit leftUnit, double width, Style.Unit widthUnit)` Overloaded version for IsWidget.
`void` `setWidgetLeftWidth(Widget child, double left, Style.Unit leftUnit, double width, Style.Unit widthUnit)` Sets the child widget's left and width values.
`void` `setWidgetRightWidth(IsWidget child, double right, Style.Unit rightUnit, double width, Style.Unit widthUnit)` Overloaded version for IsWidget.
`void` `setWidgetRightWidth(Widget child, double right, Style.Unit rightUnit, double width, Style.Unit widthUnit)` Sets the child widget's right and width values.
`void` `setWidgetTopBottom(IsWidget child, double top, Style.Unit topUnit, double bottom, Style.Unit bottomUnit)` Overloaded version for IsWidget.
`void` `setWidgetTopBottom(Widget child, double top, Style.Unit topUnit, double bottom, Style.Unit bottomUnit)` Sets the child widget's top and bottom values.
`void` `setWidgetTopHeight(IsWidget child, double top, Style.Unit topUnit, double height, Style.Unit heightUnit)` Overloaded version for IsWidget.
`void` `setWidgetTopHeight(Widget child, double top, Style.Unit topUnit, double height, Style.Unit heightUnit)` Sets the child widget's top and height values.
`void` `setWidgetVerticalPosition(Widget child, Layout.Alignment position)` Sets the child widget's vertical position within its layer.
`void` `setWidgetVisible(Widget child, boolean visible)` Shows or hides the given widget and its layer.

### Methods inherited from class com.google.gwt.user.client.ui.ComplexPanel

`add, add, adjustIndex, checkIndexBoundsForAccess, checkIndexBoundsForInsertion, doLogicalClear, getChildren, getWidget, getWidgetCount, getWidgetIndex, getWidgetIndex, insert, insert, iterator, remove`

### Methods inherited from class com.google.gwt.user.client.ui.Panel

`add, adopt, clear, doAttachChildren, doDetachChildren, orphan, remove`

### Methods inherited from class com.google.gwt.user.client.ui.Widget

`addAttachHandler, addBitlessDomHandler, addDomHandler, addHandler, asWidget, asWidgetOrNull, createHandlerManager, delegateEvent, ensureHandlers, fireEvent, getHandlerCount, getHandlerManager, getLayoutData, getParent, isAttached, isOrWasAttached, onBrowserEvent, onLoad, onUnload, removeFromParent, replaceElement, setLayoutData, setParent, sinkEvents, unsinkEvents`

### Methods inherited from class com.google.gwt.user.client.ui.UIObject

`addStyleDependentName, addStyleName, ensureDebugId, ensureDebugId, ensureDebugId, getAbsoluteLeft, getAbsoluteTop, getElement, getOffsetHeight, getOffsetWidth, getStyleElement, getStyleName, getStyleName, getStylePrimaryName, getStylePrimaryName, getTitle, isVisible, isVisible, onEnsureDebugId, removeStyleDependentName, removeStyleName, resolvePotentialElement, setElement, setElement, setHeight, setPixelSize, setSize, setStyleDependentName, setStyleName, setStyleName, setStyleName, setStyleName, setStylePrimaryName, setStylePrimaryName, setTitle, setVisible, setVisible, setWidth, sinkBitlessEvent, toString`

### Methods inherited from class java.lang.Object

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

### Methods inherited from interface java.lang.Iterable

`forEach, spliterator`

### Constructor Detail

#### LayoutPanel

    public LayoutPanel()

Creates an empty layout panel.

### Method Detail

#### add

    public void add(Widget widget)

Adds a widget to this panel.

By default, each child will fill the panel. To build more interesting layouts, set child widgets' layout constraints using `setWidgetLeftRight(Widget, double, Style.Unit, double, Style.Unit)` and related methods.

Specified by:
  `add` in interface `HasWidgets`
Overrides:
  `add` in class `Panel`
Parameters:
  `widget` - the widget to be added
See Also:
  `HasWidgets.add(Widget)`

#### animate

    public void animate(int duration)

Description copied from interface: `AnimatedLayout`
Layout children, animating over the specified period of time.

Specified by:
  `animate` in interface `AnimatedLayout`
Parameters:
  `duration` - the animation duration, in milliseconds

#### animate

    public void animate(int duration,
                        Layout.AnimationCallback callback)

Description copied from interface: `AnimatedLayout`
Layout children, animating over the specified period of time.

This method provides a callback that will be informed of animation updates. This can be used to create more complex animation effects.

Specified by:
  `animate` in interface `AnimatedLayout`
Parameters:
  `duration` - the animation duration, in milliseconds
  `callback` - the animation callback

#### forceLayout

    public void forceLayout()

Description copied from interface: `AnimatedLayout`
Layout children immediately.

This is not normally necessary, unless you want to update child widgets' positions explicitly to create a starting point for a subsequent call to `AnimatedLayout.animate(int)`.

Specified by:
  `forceLayout` in interface `AnimatedLayout`
See Also:
  `AnimatedLayout.animate(int)`, `AnimatedLayout.animate(int, Layout.AnimationCallback)`

#### getWidgetContainerElement

    public Element getWidgetContainerElement(Widget child)

Gets the container element wrapping the given child widget.

Parameters:
  `child` -
Returns:
  the widget's container element

#### insert

    public void insert(Widget widget,
                       int beforeIndex)

Inserts a widget before the specified index.

By default, each child will fill the panel. To build more interesting layouts, set child widgets' layout constraints using `setWidgetLeftRight(Widget, double, Style.Unit, double, Style.Unit)` and related methods.

Inserting a widget in this way has no effect on the DOM structure, but can be useful for other panels that wrap LayoutPanel to maintain insertion order.

Parameters:
  `widget` - the widget to be inserted
  `beforeIndex` - the index before which it will be inserted
Throws:
  `java.lang.IndexOutOfBoundsException` - if `beforeIndex` is out of range

#### onResize

    public void onResize()

Description copied from interface: `RequiresResize`
This method must be called whenever the implementor's size has been modified.

Specified by:
  `onResize` in interface `RequiresResize`

#### remove

    public boolean remove(Widget w)

Description copied from class: `Panel`
Removes a child widget.

How to Override this Method

There are several important things that must take place in the correct order to properly remove a Widget from a Panel. Not all of these steps will be relevant to every Panel, but all of the steps must be considered.

1. Validate: Make sure this Panel is actually the parent of the child Widget; return `false` if it is not.
2. Orphan: Call `Panel.orphan(Widget)` first while the child Widget is still attached.
3. Physical Detach: Adjust the DOM to account for the removal of the child Widget. The Widget's Element must be physically removed from the DOM.
4. Logical Detach: Update the Panel's state variables to reflect the removal of the child Widget. Example: the Widget is removed from the Panel's `WidgetCollection`.

Specified by:
  `remove` in interface `HasWidgets`
Overrides:
  `remove` in class `ComplexPanel`
Parameters:
  `w` - the widget to be removed
Returns:
  `true` if the child was present

#### setWidgetBottomHeight

    public void setWidgetBottomHeight(Widget child,
                                      double bottom,
                                      Style.Unit bottomUnit,
                                      double height,
                                      Style.Unit heightUnit)

Sets the child widget's bottom and height values.

Parameters:
  `child` -
  `bottom` -
  `bottomUnit` -
  `height` -
  `heightUnit` -

#### setWidgetBottomHeight

    public void setWidgetBottomHeight(IsWidget child,
                                      double bottom,
                                      Style.Unit bottomUnit,
                                      double height,
                                      Style.Unit heightUnit)

Overloaded version for IsWidget.

See Also:
  `setWidgetBottomHeight(Widget,double, Style.Unit, double, Style.Unit)`

#### setWidgetHorizontalPosition

    public void setWidgetHorizontalPosition(Widget child,
                                            Layout.Alignment position)

Sets the child widget's horizontal position within its layer.

Parameters:
  `child` -
  `position` -

#### setWidgetLeftRight

    public void setWidgetLeftRight(Widget child,
                                   double left,
                                   Style.Unit leftUnit,
                                   double right,
                                   Style.Unit rightUnit)

Sets the child widget's left and right values.

Parameters:
  `child` -
  `left` -
  `leftUnit` -
  `right` -
  `rightUnit` -

#### setWidgetLeftRight

    public void setWidgetLeftRight(IsWidget child,
                                   double left,
                                   Style.Unit leftUnit,
                                   double right,
                                   Style.Unit rightUnit)

Overloaded version for IsWidget.

See Also:
  `setWidgetLeftRight(Widget,double, Style.Unit, double, Style.Unit)`

#### setWidgetLeftWidth

    public void setWidgetLeftWidth(Widget child,
                                   double left,
                                   Style.Unit leftUnit,
                                   double width,
                                   Style.Unit widthUnit)

Sets the child widget's left and width values.

Parameters:
  `child` -
  `left` -
  `leftUnit` -
  `width` -
  `widthUnit` -

#### setWidgetLeftWidth

    public void setWidgetLeftWidth(IsWidget child,
                                   double left,
                                   Style.Unit leftUnit,
                                   double width,
                                   Style.Unit widthUnit)

Overloaded version for IsWidget.

See Also:
  `setWidgetLeftWidth(Widget,double, Style.Unit, double, Style.Unit)`

#### setWidgetRightWidth

    public void setWidgetRightWidth(Widget child,
                                    double right,
                                    Style.Unit rightUnit,
                                    double width,
                                    Style.Unit widthUnit)

Sets the child widget's right and width values.

Parameters:
  `child` -
  `right` -
  `rightUnit` -
  `width` -
  `widthUnit` -

#### setWidgetRightWidth

    public void setWidgetRightWidth(IsWidget child,
                                    double right,
                                    Style.Unit rightUnit,
                                    double width,
                                    Style.Unit widthUnit)

Overloaded version for IsWidget.

See Also:
  `setWidgetRightWidth(Widget,double, Style.Unit, double, Style.Unit)`

#### setWidgetTopBottom

    public void setWidgetTopBottom(Widget child,
                                   double top,
                                   Style.Unit topUnit,
                                   double bottom,
                                   Style.Unit bottomUnit)

Sets the child widget's top and bottom values.

Parameters:
  `child` -
  `top` -
  `topUnit` -
  `bottom` -
  `bottomUnit` -

#### setWidgetTopBottom

    public void setWidgetTopBottom(IsWidget child,
                                   double top,
                                   Style.Unit topUnit,
                                   double bottom,
                                   Style.Unit bottomUnit)

Overloaded version for IsWidget.

See Also:
  `setWidgetTopBottom(Widget,double, Style.Unit, double, Style.Unit)`

#### setWidgetTopHeight

    public void setWidgetTopHeight(Widget child,
                                   double top,
                                   Style.Unit topUnit,
                                   double height,
                                   Style.Unit heightUnit)

Sets the child widget's top and height values.

Parameters:
  `child` -
  `top` -
  `topUnit` -
  `height` -
  `heightUnit` -

#### setWidgetTopHeight

    public void setWidgetTopHeight(IsWidget child,
                                   double top,
                                   Style.Unit topUnit,
                                   double height,
                                   Style.Unit heightUnit)

Overloaded version for IsWidget.

See Also:
  `setWidgetTopHeight(Widget,double, Style.Unit, double, Style.Unit)`

#### setWidgetVerticalPosition

    public void setWidgetVerticalPosition(Widget child,
                                          Layout.Alignment position)

Sets the child widget's vertical position within its layer.

Parameters:
  `child` -
  `position` -

#### setWidgetVisible

    public void setWidgetVisible(Widget child,
                                 boolean visible)

Shows or hides the given widget and its layer. This method explicitly calls `UIObject.setVisible(boolean)` on the child widget and ensures that its associated layer is shown/hidden.

Parameters:
  `child` -
  `visible` -

#### onAttach

    protected void onAttach()

Description copied from class: `Widget`

This method is called when a widget is attached to the browser's document. To receive notification after a Widget has been added to the document, override the `Widget.onLoad()` method or use `Widget.addAttachHandler(com.google.gwt.event.logical.shared.AttachEvent.Handler)`.

It is strongly recommended that you override `Widget.onLoad()` or `Widget.doAttachChildren()` instead of this method to avoid inconsistencies between logical and physical attachment states.

Subclasses that override this method must call `super.onAttach()` to ensure that the Widget has been attached to its underlying Element.

Overrides:
  `onAttach` in class `Widget`
See Also:
  `Widget.onLoad()`, `Widget.doAttachChildren()`

#### onDetach

    protected void onDetach()

Description copied from class: `Widget`

This method is called when a widget is detached from the browser's document. To receive notification before a Widget is removed from the document, override the `Widget.onUnload()` method or use `Widget.addAttachHandler(com.google.gwt.event.logical.shared.AttachEvent.Handler)`.

It is strongly recommended that you override `Widget.onUnload()` or `Widget.doDetachChildren()` instead of this method to avoid inconsistencies between logical and physical attachment states.

Subclasses that override this method must call `super.onDetach()` to ensure that the Widget has been detached from the underlying Element. Failure to do so will result in application memory leaks due to circular references between DOM Elements and JavaScript objects.

Overrides:
  `onDetach` in class `Widget`
See Also:
  `Widget.onUnload()`, `Widget.doDetachChildren()`

#### getLayout

    Layout getLayout()

Gets the `Layout` instance associated with this widget. This is made package-protected for use by `RootLayoutPanel`.

Returns:
  this widget's layout instance