我正在与MVC作战，我正在制作一个简单的计算器。我有4个班级，主要，模型，视图和控制器。问题是我在尝试将一个Listener与我的Controller类连接时得到NullPointer，它有一个嵌套类。我在互联网上看到了类似的解决方案，但我无法让它发挥作用。无论如何，这是代码：
public class CView {
public JPanel panel;
private JButton b1, b2, b3, b4, b5, b6, b7 , b8, b9, b0, bDel, bDiv, bMul, bAdd, bSub, bRes;
public JTextField t;
private String value;
public int tValue1 = 0;
public int tValue2 = 0;
public JPanel makePanel() {
panel = new JPanel();
panel.setLayout(null);
t = new JTextField();
b1 = new JButton("1");
b2 = new JButton("2");
b3 = new JButton("3");
b4 = new JButton("4");
b5 = new JButton("5");
b6 = new JButton("6");
b7 = new JButton("7");
b8 = new JButton("8");
b9 = new JButton("9");
b0 = new JButton("0");
bDel = new JButton("Del");
bDiv = new JButton("/");
bMul = new JButton("*");
bAdd = new JButton("+");
bSub = new JButton("-");
//bClr = new JButton("CLC");
bRes = new JButton("=");
b1.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
value = ((JButton)e.getSource()).getText();
t.setText(t.getText()+value);
}
});
b2.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
value = ((JButton)e.getSource()).getText();
t.setText(t.getText()+value);
}
});
b3.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
value = ((JButton)e.getSource()).getText();
t.setText(t.getText()+value);
}
});
b4.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
value = ((JButton)e.getSource()).getText();
t.setText(t.getText()+value);
}
});
b5.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
value = ((JButton)e.getSource()).getText();
t.setText(t.getText()+value);
}
});
b6.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
value = ((JButton)e.getSource()).getText();
t.setText(t.getText()+value);
}
});
b7.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
value = ((JButton)e.getSource()).getText();
t.setText(t.getText()+value);
}
});
b8.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
value = ((JButton)e.getSource()).getText();
t.setText(t.getText()+value);
}
});
b9.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
value = ((JButton)e.getSource()).getText();
t.setText(t.getText()+value);
}
});
b0.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
value = ((JButton)e.getSource()).getText();
t.setText(t.getText()+value);
}
});
bDel.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
t.setText(t.getText().substring(0, t.getText().length()-1));
}
});
bDiv.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
getValue1();
}
});
panel.add(b7);
panel.add(b8);
panel.add(b9);
panel.add(b4);
panel.add(b5);
panel.add(b6);
panel.add(b1);
panel.add(b2);
panel.add(b3);
panel.add(b0);
panel.add(bRes);
panel.add(bDel);
panel.add(bDiv);
panel.add(bMul);
panel.add(bAdd);
panel.add(bSub);
panel.add(t);
t.setBounds(30,40,280,30);
b7.setBounds(40,100,50,40);
b8.setBounds(110,100,50,40);
b9.setBounds(180,100,50,40);
bDiv.setBounds(250,100,50,40);
b4.setBounds(40,170,50,40);
b5.setBounds(110,170,50,40);
b6.setBounds(180,170,50,40);
bMul.setBounds(250,170,50,40);
b1.setBounds(40,240,50,40);
b2.setBounds(110,240,50,40);
b3.setBounds(180,240,50,40);
bSub.setBounds(250,240,50,40);
bDel.setBounds(40,310,60,40);
b0.setBounds(110,310,50,40);
bRes.setBounds(180,310,60,40);
bAdd.setBounds(250,310,50,40);
panel.setVisible(true);
return panel;
}
void divCalculateListener(ActionListener l){
bRes.addActionListener(l); //here is the problem
}
public int getValue1() {
tValue1 = Integer.parseInt(t.getText());
t.setText("");
return tValue1;
}
public int getValue2() {
tValue2 = Integer.parseInt(t.getText());
t.setText("");
return tValue2;
}
public void setResult(int res) {
t.setText(Integer.toString(res));
System.out.println("Ispis");
}
}
这是Controller类：
public class Controller {
private Model model;
private CView view;
public Controller(Model model, CView view) {
this.model = model;
this.view = view;
this.view.divCalculateListener(new CalculateListener());
}
class CalculateListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
view.getValue2();
try {
model.divide(view.getValue1(), view.getValue2());
view.setResult(model.getResult());
} catch (NumberFormatException ne) {
}
}
}
}
正如您所看到的here，当他们尝试连接按钮时，它们使用与我完全相同的格式。提前谢谢。