[英]JLabel wont change color twice
I have the following code: 我有以下代码:
public class Test extends JFrame implements ActionListener{
private static final Color TRANSP_WHITE = new Color(new Float(1), new Float(1), new Float(1), new Float(0.5));
private static final Color TRANSP_RED = new Color(new Float(1), new Float(0), new Float(0), new Float(0.1));
private static final Color[] COLORS = new Color[]{ TRANSP_RED, TRANSP_WHITE};
private int index = 0;
private JLabel label;
private JButton button;
public Test(){
super();
setLayout(new BoxLayout(getContentPane(), BoxLayout.Y_AXIS));
label = new JLabel("hello world");
label.setOpaque(true);
label.setBackground(TRANSP_WHITE);
getContentPane().add(label);
button = new JButton("Click Me");
button.addActionListener(this);
getContentPane().add(button);
pack();
setVisible(true);
}
@Override
public void actionPerformed(ActionEvent e) {
if(e.getSource().equals(button)){
label.setBackground(COLORS[index % (COLORS.length - 1)]);
index++;
}
}
public static void main(String[] args) {
new Test();
}
}
When I run it I get the label with the TRANSP_WHITE
background and then when I click the button this color changes to TRANSP_RED
but when I click it again I see no change in color. 当我运行它时,我得到带有TRANSP_WHITE
背景的标签,然后当我单击按钮时,该颜色变为TRANSP_RED
但是当我再次单击它时,我看到颜色没有变化。 Does anyone know why? 有人知道为什么吗?
Thanks 谢谢
Well, what were you expecting to happen? 好吧,您期望发生什么?
label.setBackground(COLORS[index % (COLORS.length - 1)]);
The index variable is hard coded to 0. and COLORS.length -1 is essentially a constant. index变量被硬编码为0。COLORS.length-1本质上是一个常数。 So every time you click your setting the background to COLORS[0]; 因此,每次单击将背景设置为COLORS [0]时;
If you change your action method to the following you'll get the results you are looking for: 如果将操作方法更改为以下内容,则会得到所需的结果:
@Override
public void actionPerformed(ActionEvent e) {
if(e.getSource().equals(button)){
label.setBackground(COLORS[index % COLORS.length]);
index++;
}
}
First: The modulo operator will always return a value between 0 and one less than the value passed to it. 第一:模运算符将始终返回一个比传递给它的值小0到一个之间的值。 So 所以
index % COLORS.length
Will always return a value between 0 and COLORS.length -1. 将始终返回介于0和COLORS.length -1之间的值。
Second: You were forgetting to increment index after every call. 第二:您忘记了在每次调用后增加索引。
Hey! 嘿! You forgot to increment index. 您忘记增加索引。 In this expression: 在此表达式中:
label.setBackground(COLORS[index % (COLORS.length - 1)]);
index % (COLORS.length - 1)
is always 0. index % (COLORS.length - 1)
始终为0。
BTW. 顺便说一句。 you don't have to use new Float(1)
when creating Color
. 创建Color
时不必使用new Float(1)
。 1F
should work too. 1F
应该工作。
这是您必须使用的代码
label.setBackground(COLORS[index % (COLORS.length)]);
index++;
You are doing it wrong. 你做错了。 It should be done like that 应该那样做
label = new JLabel("hello world"){
public void paintComponent(Graphics g)
{
//draw background
Color old=g.getColor();
g.setColor(getBackground());
g.fillRect(0,0,getWidth(),getHeight());
g.setColor(old);
super.paintComponent(g);
}
};
label.setOpaque(false); // your component is not opaque!
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