GridBagLayout

GridBagLayout的使用：

GridBagLayout是java中最有弹性但也是最复杂的一种版面管理器。它只有一种构造函数，但必须配合GridBagConstraints才能达到设置的效果。 GridBagLayout的类层次结构图：

java.lang.Object     --java.awt.GridBagLayout

构造函数：

GirdBagLayout()建立一个新的GridBagLayout管理器。
GridBagConstraints()建立一个新的GridBagConstraints对象。
GridBagConstraints(int gridx,int gridy,int gridwidth,int gridheight,double weightx,double weighty, int anchor,int fill, Insets insets,int ipadx,int ipady)建立一个新的GridBagConstraints对象 ，并指定其参数的值。

参数说明:

gridx,gridy:设置组件的位置，gridx设置为GridBagConstraints.RELATIVE代表此组件位于之前所加入组件的右边。 若将gridy设置为GridBagConstraints.RELATIVE代表此组件位于以前所加入组件的下面。建议定义出gridx,gridy的位置，以便以后维护程序。表示放在几行几列，gridx=0,gridy=0时放在0行0列。

gridwidth,gridheight:用来设置组件所占的单位长度与高度，默认值皆为1。你可以使用GridBagConstraints.REMAINDER常 量，代表此组件为此行或此列的最后一个组件，而且会占据所有剩余的空间。

weightx,weighty:用来设置窗口变大时，各组件跟着变大的比例，当数字越大，表示组件能得到更多的空间，默认值皆为0。

anchor:当组件空间大于组件本身时，要将组件置于何处，有CENTER(默认值)、NORTH、NORTHEAST、EAST、SOUTHEAST、 WEST、NORTHWEST可供选择。

insets:设置组件之间彼此的间距，它有四个参数，分别是上，左，下，右，默认为(0,0,0,0).

ipadx,ipady:设置组件内的间距，默认值为0。

我们以前提过，GridBagLayout里的各种设置都必须通过GridBagConstraints,因此当我们将GridBagConstraints的参数都设置 好了之后，必须new一个GridBagConstraints的对象出来，以便GridBagLayout使用。

例子： GridBagLayoutDemo.java

import java.awt.*;import java.awt.event.*;import javax.swing.*;public class GridBagLayoutDemo {public GridBagLayoutDemo() {JButton b;GridBagConstraints c;int gridx, gridy, gridwidth, gridheight, anchor, fill, ipadx, ipady;double weightx, weighty;Insets inset;JFrame f = new JFrame();GridBagLayout gridbag = new GridBagLayout();Container contentPane = f.getContentPane();contentPane.setLayout(gridbag);b = new JButton("first");gridx = 0;gridy = 0;gridwidth = 1;gridheight = 1;weightx = 10;weighty = 1;anchor = GridBagConstraints.CENTER;fill = GridBagConstraints.HORIZONTAL;inset = new Insets(0, 0, 0, 0);ipadx = 0;ipady = 0;c = new GridBagConstraints(gridx, gridy, gridwidth, gridheight,weightx, weighty, anchor, fill, inset, ipadx, ipady);gridbag.setConstraints(b, c);contentPane.add(b);b = new JButton("second");gridx = 1;gridy = 0;gridwidth = 2;gridheight = 1;weightx = 1;weighty = 1;anchor = GridBagConstraints.CENTER;fill = GridBagConstraints.HORIZONTAL;inset = new Insets(0, 0, 0, 0);ipadx = 50;ipady = 0;c = new GridBagConstraints(gridx, gridy, gridwidth, gridheight,weightx, weighty, anchor, fill, inset, ipadx, ipady);gridbag.setConstraints(b, c);contentPane.add(b);b = new JButton("third");gridx = 0;gridy = 1;gridwidth = 1;gridheight = 1;weightx = 1;weighty = 1;anchor = GridBagConstraints.CENTER;fill = GridBagConstraints.HORIZONTAL;inset = new Insets(0, 0, 0, 0);ipadx = 0;ipady = 50;c = new GridBagConstraints(gridx, gridy, gridwidth, gridheight,weightx, weighty, anchor, fill, inset, ipadx, ipady);gridbag.setConstraints(b, c);contentPane.add(b);b = new JButton("fourth");gridx = 1;gridy = 1;gridwidth = 1;gridheight = 1;weightx = 1;weighty = 1;anchor = GridBagConstraints.CENTER;fill = GridBagConstraints.HORIZONTAL;inset = new Insets(0, 0, 0, 0);ipadx = 0;ipady = 0;c = new GridBagConstraints(gridx, gridy, gridwidth, gridheight,weightx, weighty, anchor, fill, inset, ipadx, ipady);gridbag.setConstraints(b, c);contentPane.add(b);b = new JButton("This is the last button");gridx = 2;gridy = 1;gridwidth = 1;gridheight = 2;weightx = 1;weighty = 1;anchor = GridBagConstraints.CENTER;fill = GridBagConstraints.HORIZONTAL;inset = new Insets(0, 0, 0, 0);ipadx = 0;ipady = 50;c = new GridBagConstraints(gridx, gridy, gridwidth, gridheight,weightx, weighty, anchor, fill, inset, ipadx, ipady);gridbag.setConstraints(b, c);contentPane.add(b);f.setTitle("GridBagLayout");f.pack();f.setVisible(true);f.addWindowListener(new WindowAdapter() {public void windowClosing(WindowEvent e) {System.exit(0);}});}public static void main(String[] args) {new GridBagLayoutDemo();}} 

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