Error when call method from another class in android

Question

i have 2 class. One is MainBaby.java and it contains:

public class MainBaby extends SurfaceView implements SurfaceHolder.Callback {

public MainBaby(Context context){
    super(context);
    init();
}

public MainBaby(Context context, AttributeSet attrs) {
      super(context, attrs);
      // TODO Auto-generated constructor stub
      init();
}

public MainBaby(Context context, AttributeSet attrs, int defStyle) {
      super(context, attrs, defStyle);
      // TODO Auto-generated constructor stub
      init();
}

public void init(){
    // adding the callback (this) to the surface holder to intercept events

    getHolder().addCallback(this);

    // create the game loop thread
    thread = new ThreadBaby(getHolder(), this);

    mPath = new Path();
    mBitmapPaint = new Paint(Paint.DITHER_FLAG);
    p = new Paint();
    p.setAntiAlias(true);
    p.setDither(true);
    p.setColor(Color.BLACK);
    p.setStyle(Paint.Style.STROKE);
    p.setStrokeJoin(Paint.Join.ROUND);
    p.setStrokeCap(Paint.Cap.ROUND);
    p.setStrokeWidth(50);

    setFocusable(true);

}

public void callMe(){

    Log.v("tag", "the button successfully pressed");
}   
}

this class in inflated in main.xml

<AbsoluteLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
  <coba.gesture.Main
    android:id="@+id/LayoDalam"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" />
</AbsoluteLayout>

and i want to call method callMe() at cobaGesture.java like this:

public class CobaGesture extends Activity { MainBaby mb;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);  
    ImageButton resetBut = (ImageButton) findViewById(R.id.reset);
    resetBut.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            mb.callMe();
        }
    });      
}

but when i click the button, the application was force closed and here's the logcat:

05-30 10:55:58.433: ERROR/AndroidRuntime(704): FATAL EXCEPTION: main
05-30 10:55:58.433: ERROR/AndroidRuntime(704): java.lang.NullPointerException
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at coba.gesture.CobaGesture$1.onClick(CobaGesture.java:41)
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at android.view.View.performClick(View.java:2485)
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at android.view.View$PerformClick.run(View.java:9080)
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at android.os.Handler.handleCallback(Handler.java:587)
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at android.os.Handler.dispatchMessage(Handler.java:92)
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at android.os.Looper.loop(Looper.java:123)
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at android.app.ActivityThread.main(ActivityThread.java:3647)
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at java.lang.reflect.Method.invokeNative(Native Method)
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at java.lang.reflect.Method.invoke(Method.java:507)
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
05-30 10:55:58.433: ERROR/AndroidRuntime(704):     at dalvik.system.NativeStart.main(Native Method)

what does it means? and how to solve it?

thank you in advance.

UPDATE! here's the edited code and the error: enter image description here

score 2 · Accepted Answer · edited May 23 '17 at 12:19

2

You should initial object with the correct context (in this case, it is your activity). So it is:

  mb = new MainBaby(CobaGesture.this);
OR:
  mb = new MainBaby(getApplicationContext());

Put this code into onClick event or onCreate, so you can use mb.callMe();

All about the context is here and from Android document

edited May 23 '17 at 12:19

Community

1
1

answered May 30 '12 at 04:50

ductran

10,043
19
82
165

score 0 · Answer 2 · answered May 30 '12 at 04:05

0

mb.callMe();

Is not institiated thats the reason of the error. In other words, you are using a variable that points to nothing or Null. If you want to use other classes in your code your should declare it first.

public void onClick(View v) {
 MainBaby mb = new MainBaby(); //This initiates the variable correctly.
 mb.callMe();
}

answered May 30 '12 at 04:05

Shiin Zu

166
9

when i used the code above, it display error. it says "add argument to match MainBaby(context)", "add argument to match MainBaby(context, attrs)", "add argument to match MainBaby(context, attrs, defStyle)" – abuybuy May 30 '12 at 04:21
I didn't pay attention that the MainBaby class had parameters in the constructor, my bad. – Shiin Zu May 30 '12 at 17:36

Ponmalar · Answer 3 · 2012-05-30T04:56:20.190

0

Initialize the object mb as mb=new MainBaby(CobaGesture.this); inside the oncreate method

edited May 30 '12 at 04:56

answered May 30 '12 at 04:07

Ponmalar

6,871
10
50
80

i've used the code above, it display error. it says "add argument to match MainBaby(context)", "add argument to match MainBaby(context, attrs)", "add argument to match MainBaby(context, attrs, defStyle)" – – abuybuy May 30 '12 at 04:22
i've posted the image. please check it out. – abuybuy May 30 '12 at 04:41
see the edited code, Mainbaby has the contructor with paramater, so while creating the object we have to pass context of this CabaGesture class. – Ponmalar May 30 '12 at 04:56

score -2 · Answer 4 · answered Feb 18 '14 at 11:46

callme() is a method of android which is called when in view when we pressed any button . just put this below method in activity which contain atleast one button and run your project .

 public void callMe(View view){

            Log.e("tag", "the button successfully pressed");
        }

Error when call method from another class in android

4 Answers4

Linked