问题
I am new to Java and especially new to GUI and it's super confusing to me right now.
I'm making a program for class that is supposed to have a menu (JComboBox I'm assuming) that opens a new window when an option is selected. I am just working on the first option where you click "The Matrix" and a new window pops up with two buttons called "Red Pill" & "Blue Pill" and thats where I've hit a wall.
I got to the point where I am able to create a new window (not sure if this is even the right route to take for opening the new window) but, When I try to add Buttons to the new pop up window nothing shows up....
Thanks for any help or pointers in the right direction!
public class MultiForm extends JFrame{
private JComboBox menu;
private JButton bluePill;
private JButton redPill;
private static String[] fileName = {"", "The Matrix", "Another Option"};
public MultiForm() {
super("Multi Form Program");
setLayout(new FlowLayout());
menu = new JComboBox(fileName);
add(menu);
TheHandler handler = new TheHandler();
menu.addActionListener(handler);
}
private class TheHandler implements ActionListener{
public void actionPerformed(ActionEvent event) {
********************************************************************
//Create a new window when "The Matrix" is clicked in the JCB
JFrame newFrame = new JFrame();
JPanel panel = new JPanel();
newFrame.setLayout(new FlowLayout());
newFrame.setSize(500, 300);
newFrame.setDefaultCloseOperation(newFrame.EXIT_ON_CLOSE);
Icon bp = new ImageIcon(getClass().getResource("Blue Pill.png"));
bluePill = new JButton("Blue Pill", bp);
newFrame.add(bluePill);
Icon rp = new ImageIcon(getClass().getResource("Red Pill.png"));
redPill = new JButton("Red Pill", rp);
newFrame.add(redPill);
add(panel);
newFrame.setVisible(true);
}
}
public static void main(String[] args) {
MultiForm go = new MultiForm();
go.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
go.setSize(400, 200);
go.setVisible(true);
}
}
回答1:
I tried doing newFrame.add(BluePill) and it created a button that was the size of the entire window and it would not allow me to add both buttons that way
That's because the frame uses a BorderLayout by default. Unless you specify otherwise, the component's will be added to the CENTER position, BUT, BorderLayout will only allow a single component to be managed at each of the it's five available positions, so you are only seeing the last component you added.
See How to Use BorderLayout for more details
so I figured that wasn't the correct way
It's the right approach, you just need to use a layout manager which can accommodate more components or change the position which you are adding the buttons
In this little example, I've just use a FlowLayout, but you can use what ever is going to give you the effect you desire
JFrame newFrame = new JFrame();
newFrame.setLayout(new FlowLayout());
newFrame.setDefaultCloseOperation(newFrame.EXIT_ON_CLOSE);
bluePill = new JButton("Blue Pill");
newFrame.add(bluePill);
redPill = new JButton("Red Pill");
newFrame.add(redPill);
newFrame.pack();
newFrame.setVisible(true);
As a general rule of thumb, I don't like adding components like this directly to a top level container, I prefer to use a intermediate container, like a JPanel, this gives me more possibilities for re-use, but that's me.
You should also only make the frame visible when it's actually ready, otherwise you may find that some times, the components won't show up
See Laying Out Components Within a Container for more details
回答2:
You are not using the getContentPane() method from the new JFrame.
You have to actually use getContentPane() first because you're not adding any component to the JFrame itself but to an intermediate "panel".
JFrame newFrame = new JFrame();
JPanel panel = new JPanel();
newFrame.setSize(300, 200);
newFrame.setDefaultCloseOperation(newFrame.EXIT_ON_CLOSE);
bluePill = new JButton("Blue Pill");
panel.add(bluePill);
redPill = new JButton("Red Pill");
panel.add(redPill);
newFrame.getContentPane().add(panel);
newFrame.setVisible(true);
You'll have to add a Layout to the JPanel or/and the JFrame and play with the sizes of the component but with this you're on the right path.
I always put the setVisible method a the end, after adding all the components to the frame.
回答3:
You made some mistakes.
add(bluePill);
will not do what you want, even if it would, it would still be wrong. (sounds weird, but I'll explain it)
First the "right" way to do it:
//Create a new window when "The Matrix" is clicked in the JCB
JFrame newFrame = new JFrame();
newFrame.setSize(300, 200);
newFrame.setDefaultCloseOperation(newFrame.EXIT_ON_CLOSE);
bluePill = new JButton("Blue Pill");
newFrame.getContentPane().add(bluePill);
redPill = new JButton("Red Pill");
newFrame.getContentPane().add(redPill);
newFrame.setVisible(true);
Notice I added "newFrame", because you were calling the method of MultiForm. That's because "add()" is the same as "this.add()" and "this" points to MultiForm. Check it with this line if you want:
System.out.println(this.toString());
The "getContentPane()" is best explained with this image:
You were adding it directly to the JFrame (I don't even know what exactly happens then).
It is also good practice to set the frame visible when it is ready to be visible. Your frame did not contain anything when you made it visible.
Now to the JPanel. A JPanel can hold some elements like JButton,etc. and it can also have a layout. Since you didn't use the JPanel at all, i removed the line from your code. You can still add the JPanel to your ContentPane and add a Layout to the JPanel. (You can also add JPanels to JPanels to create complex layouts)
I hope this was clear for you.
来源：https://stackoverflow.com/questions/32750611/gui-jcombobox-and-opening-a-new-window