为什么在Java awt GridBagLayout中，gridwidth或gridheight跨度比指定的少一行或少一列？

Question

我正在用GridBagLayout编写一个简单的awt程序，其中有四个使用gridx，gridy对角排列的按钮。当我将gridwidth设置为3时，它仅跨2列，并且忽略了自己的列。这与gridheight相同（跨度少1行）。

import java.applet.Applet;
import java.awt.Button;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;

public class Second extends Applet{
@Override
public void init()
{
    GridBagLayout bl = new GridBagLayout();
    this.setLayout(bl);
    GridBagConstraints gc = new GridBagConstraints();
    gc.gridx = 0;
    gc.gridy= 0;

    gc.gridwidth = 4;
    gc.fill = GridBagConstraints.HORIZONTAL;

    Button btemp = new Button("Button1");
    add(btemp, gc);

    gc.gridx = 1;
    gc.gridy= 1;
    gc.gridwidth = 1;
    add(new Button("Button2"), gc);

    gc.gridx = 2;
    gc.gridy= 2;
    add(new Button("Button3"), gc);

    gc.gridx = 3;
    gc.gridy= 3;
    add(new Button("Button4"), gc);
    setVisible(true);
}
}

Answer 1

问题中的原始代码如下所示：

您想要它像这样渲染，对吧？

好吧...我通过在add(new Button("Button4"), gc);行之后添加这些行来制作该图像。 （您添加Components的顺序似乎不会影响结果。）

    //First, let us tell AWT to figure out the sizes of components
    //  it has so far.  If we do not do this, calls to getWidth()
    //  will return 0 sometimes!  It appears to be a race condition,
    //  but that's why this layoutContainer method exists.
    bl.layoutContainer(this);

    //Now, let us target the missing grid cell.
    gc.gridx = 0;
    gc.gridy = 1;

    //Let us put something in there, so the whole column has a
    //  non-zero width.  Using the width of an existing button
    //  is better than just picking some number of pixels.
    add(Box.createHorizontalStrut(this.getComponent(2).getWidth()),gc);

    //Let us adjust the applet window size (optional)
    this.setSize(this.getComponent(2).getWidth() * 4, 200);

您是否愿意在网格中的那个位置粘贴不可见的组件，还是需要以其他方式解决？