Package 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, 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>

  • Constructor Details

    • LayoutPanel

      public LayoutPanel()
      Creates an empty layout panel.

  • Method Details

    • 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:

    • 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:

    • 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:
      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:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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