android-java.lang.RuntimeException

Question

为什么我得到java.lang.runtimeexception：无法实例化activityComponentInfo {com.example.carprofile / com.example.carprofile.CarRegistraion}：java.lang.NullPointerExceprion

这是我的代码：

public class CarRegistration extends Activity{

//ParseXML parseClass;
Button saveCar;
EditText carMake = (EditText) findViewById(R.id.etCarMake);
EditText carModel = (EditText) findViewById(R.id.etCarModel);
String newCar;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.car_registration);

    saveCar = (Button) findViewById(R.id.bSaveCar);
    saveCar.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            newCar = carMake.getText() +" "+ carModel.getText();
            //parseClass = new ParseXML(newCar);
            //parseClass.editXML();
        }
    });
}

如果我从saveCar =（Button）...中清除onCreate方法，则一切正常。

有人可以告诉我我在做什么错吗？

Answer 1

尝试这个，

public class CarRegistration extends Activity{

     Button saveCar;
     String newCar;

@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
  super.onCreate(savedInstanceState);
  setContentView(R.layout.car_registration);

  EditText carMake = (EditText) findViewById(R.id.etCarMake); //these lines should be     after setContentView()
  EditText carModel = (EditText) findViewById(R.id.etCarModel);
  saveCar = (Button) findViewById(R.id.bSaveCar);
  saveCar.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View v) {
        newCar = carMake.getText() +" "+ carModel.getText();
        //parseClass = new ParseXML(newCar);
        //parseClass.editXML();
    }
});

}