如何使用ActionListener在画布中绘制形状？

Question

我有一个程序，该程序具有4个文本字段和一个绘制矩形的按钮，用于输入数字（x，y，x1，y1）和添加它们的按钮的文本字段（addO），我需要知道如何使用动作侦听器在画布内使用paint（）方法进行绘制 ？

Answer 1

The question is open and vague and the answer depends greatly on missing implementation details...

Essentially, getting a value from a JTextField is as simple as calling getText on an instance of the field...

private JTextField field;
//...
field = new JTextField(10);
add(field);
//...
String text = field.getText();

Converting the value to int would require you to use Integer.parseInt(text) . This will throw a NumberFormatException error if the value is not a integer value. Equally, you could just use a JSpinner instead.

Using an ActionListener is a simply as attaching an instance of ActionListener to a JButton ...

JButton doStuff = new JButton("Do Stuff");
doStuff.addActionListene(new ActionListener() {
    public void actionPerformed(ActionEvent evt) {
        // See previous comments about extract the field values...
    }
});

Painting in Swing is normally achieved by overriding paintComponent of a component that extends from JComponent , normally something like JPanel for example.

In this method you would paint whatever it is you need to...

protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawRect(x1, y1, x2, y2);
}

For example.

See:

• How to Write an Action Listener
• How to Use Buttons, Check Boxes, and Radio Buttons
• Performing Custom Painting
• 2D Graphics

For more details