A flag that indicates whether the LayoutManager allows screen updates between phases. If true, measurement and layout are done in phases, one phase per screen update. All components have their validateProperties() and commitProperties() methods called until all their properties are validated. The screen will then be updated.

Then all components will have their validateSize() and measure() methods called until all components have been measured, then the screen will be updated again.

Finally, all components will have their validateDisplayList() and updateDisplayList() methods called until all components have been validated, and the screen will be updated again. If in the validation of one phase, an earlier phase gets invalidated, the LayoutManager starts over. This is more efficient when large numbers of components are being created an initialized. The framework is responsible for setting this property.

If false, all three phases are completed before the screen is updated.

Constructor.

Returns the sole instance of this singleton class, creating it if it does not already exist.

Called when a component changes in some way that its layout and/or visuals need to be changed. In that case, it is necessary to run the component's layout algorithm, even if the component's size hasn't changed. For example, when a new child component is added, or a style property changes or the component has been given a new size by its parent.

Parameters

Adds an object to the list of components that want their validateProperties() method called. A component should call this method when a property changes. Typically, a property setter method stores a the new value in a temporary variable and calls the invalidateProperties() method so that its validateProperties() and commitProperties() methods are called later, when the new value will actually be applied to the component and/or its children. The advantage of this strategy is that often, more than one property is changed at a time and the properties may interact with each other, or repeat some code as they are applied, or need to be applied in a specific order. This strategy allows the most efficient method of applying new property values.

Parameters

Adds an object to the list of components that want their validateSize() method called. Called when an object's size changes.

An object's size can change for two reasons:

1. The content of the object changes. For example, the size of a button changes when its label is changed.
2. A script explicitly changes one of the following properties: minWidth, minHeight, explicitWidth, explicitHeight, maxWidth, or maxHeight.

When the first condition occurs, it's necessary to recalculate the measurements for the object. When the second occurs, it's not necessary to recalculate the measurements because the new size of the object is known. However, it's necessary to remeasure and relayout the object's parent.

Parameters

Returns true if there are components that need validating; false if all components have been validated.

When properties are changed, components generally do not apply those changes immediately. Instead the components usually call one of the LayoutManager's invalidate methods and apply the properties at a later time. The actual property you set can be read back immediately, but if the property affects other properties in the component or its children or parents, those other properties may not be immediately updated.

To guarantee that the values are updated, you can call the validateClient() method. It updates all properties in all components whose nest level is greater than or equal to the target component before returning. Call this method only when necessary as it is a computationally intensive call.

Parameters

When properties are changed, components generally do not apply those changes immediately. Instead the components usually call one of the LayoutManager's invalidate methods and apply the properties at a later time. The actual property you set can be read back immediately, but if the property affects other properties in the component or its children or parents, those other properties may not be immediately updated. To guarantee that the values are updated, you can call the validateNow() method. It updates all properties in all components before returning. Call this method only when necessary as it is a computationally intensive call.