GridLayout and GridData in eclipse

What the relation between th开发者_如何学Goe two? Why do you have to provide both?

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Layouts are there to give your windows a specific look. A layout controls the position and size of children in a Composite. org.eclipse.swt.layout.GridLayout is just an specific instance of org.eclipse.swt.widgets.Layout, which allows you to layout the child components of a composite in a Grid (row-column) manner.

Each widget controlled by a org.eclipse.swt.layout.GridLayout can have its initial width and height specified by setting its org.eclipse.swt.layout.GridData object.

So, the org.eclipse.swt.layout.GridLayout is basically a blue print which describes the layout of controls on a composite.

Whereas the org.eclipse.swt.layout.Griddata is the attribute of the control, describing its span, indentation, margin etc for each gird(cell). Each component should have a unique Griddata.

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In the context of SWT, GridLayout an SWT layout manager (i.e., it controls the layout of the form). GridData is a part of GridLayout and enables you to set layout properties on the SWT components participating in the layout. For instance, you can set the horizontal alignment nature of a List component by setting a GridData via cmpnt.setLayoutData(gd).

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GridLayout is the Layout Manager for the controls.

GridData specifies how the controls in each cell of the layout behave while displaying.

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GridLayout is one of standard layout managers introduced in java 1.0 15 years ago and belongs to package java.awt. GridData is a SWT extension.