java - JavaFX事件处理程序nullpointerException

我有一个带有几个不同类的Gui，它使用相同的事件处理程序。我似乎无法找到解决方案的问题是，当事件处理程序在寻找正确的方法调用并偶然发现尚未初始化的按钮时，如何避免获得nullpointerexception。
我有几个仅在用户进入createAccountGui阶段时才会初始化的按钮。

public class GuiHandler implements EventHandler<ActionEvent> {
    // this class take care off the EventHandler (buttons, all the buttons method).
    private UserGui uG;
    private AdvSearch aS;
    private LogIn logI;
    private CreateAccGui cAG;
    private OrganizerGui oG;
    private AdminGui aG;
    private PersonRegister pR;

    public GuiHandler() {
        uG = new UserGui(this);
    }

除非CreateAccGui已初始化，否则每当涉及到cAG.getRegistrate（）时，我都会得到一个nullpointerexception。有没有人有聪明的方式来处理此类问题，而不必将其拆分为几个不同的处理程序。

@Override
    public void handle(ActionEvent e) {
        try {
            //where all the button goes 2 when clicked on and perform the method they are supposed 2 do
            // UserGui class buttons
            if(e.getSource() == uG.getLogInB()) {
                logI = new LogIn(this);
            } else if (e.getSource() == uG.getAdvSearch()) {
                aS = new AdvSearch(this);
            } else if (e.getSource() == uG.getSearch()) {

            }
            // the buttons in LogIn class
            else if(e.getSource() == logI.getSignIn()) {
                signIn();
            } else if(e.getSource() == logI.getCreateAcc()) {
                logI.logInStage.close();
                cAG = new CreateAccGui(this);
            }
            //the buttons in CreateAccGui class
            else if(e.getSource() == cAG.getRegistrate()) {
                System.out.println("it stop here on registrate");
                createAccount();
            } else if(e.getSource() == cAG.getCancelReg()) {
                cAG.getCreateStage().close();
                logI = new LogIn(this);
            }
            //the buttons in AdminGui for setting text from the admin field 2 the userGui
            else if(e.getSource() == aG.getAdmLogout()) {
                aG.stage.close();
            } else if(e.getSource() == aG.getHomeAreaButton()) {
                uG.getHomeNews().setText(aG.getHomeArea().getText());
            } else if(e.getSource() == aG.getAboutButton()) {
                uG.getAboutArea().setText(aG.getAboutArea().getText());
            } else if(e.getSource() == aG.getRentButton()) {
                uG.getRentArea().setText(aG.getRentArea().getText());
            }
        } catch(NumberFormatException nfe) {
            JOptionPane.showMessageDialog(null, "Feil format på noen felter, gjerne endre på dem", "Nummer Format", JOptionPane.ERROR_MESSAGE);
        }
    } // End of Handler method
}// End of GuiHandler class

最佳答案

将空检查添加到使用cAG的代码中

     /* right here */
else if(  cAG != null  && e.getSource() == cAG.getRegistrate()) {

System.out.println("it stop here on registrate");
    createAccount();
}

&&符号short circuits如果为false，并且如果cAG.getRegistrate()为null则永远不会到达cAG

BTW JOptionPane是摆动的一部分，并且Java 8 update 40带有新的JavaFX对话框API