How to remove error when declaring an array of a class in Android

Question

Basically, I'm making a reversi app for Android, and I am currently at the point of setting up the game board. The way I am intending to do this is to create a 2D array of the position class. Each position is represented by an imageview that is used as a button which represents a board position. Here is a snippet of the code that contains the error:

setupBoard(board);
....
public void setupBoard(Position board[][]) {
    for (int y = 0; y < 8; y++) {
        for (int x = 0; x < 8; x++) {
            Log.d("Error","Error a");
            board[x][y] = new Position(getApplicationContext());
            Log.d("Error","Error b");
            board[x][y].isPositionEmpty = true;

        }
    }
}

In the position class:

public class Position {

Context myContext;
public Position(Context context) {
    Log.d("Error","Error c");
    myContext = context;
    // TODO Auto-generated constructor stub

}


public boolean isPositionEmpty = true;
public int positionID;


public  ImageView button = new ImageView(myContext);

}

The program gets to error a, but no further. The error in LogCat is: java.lang.NullPointerException

Any help will be much appreciated. Thanks in advance!

Exception: 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): 02-20 16:52:20.820: ERROR/AndroidRuntime(365): FATAL EXCEPTION: main java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{trinity.hazard.reversi/trinity.hazard.reversi.SinglePlayerActivity}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) at android.app.ActivityThread.access$2300(ActivityThread.java:125) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:123) at android.app.ActivityThread.main(ActivityThread.java:4627) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:521) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:100) at trinity.hazard.reversi.SinglePlayerActivity.(SinglePlayerActivity.java:24) at java.lang.Class.newInstanceImpl(Native Method) at java.lang.Class.newInstance(Class.java:1429) at android.app.Instrumentation.newActivity(Instrumentation.java:1021) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577) ... 11 more

m1ntf4n · Accepted Answer · 2012-02-20 15:18:25Z

2

In your Position class, try moving the line where you create the ImageView into the constructor, but AFTER initializing myContext.

answered Feb 20, 2012 at 15:18

m1ntf4n

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11 Comments

dmon Over a year ago

Oh duh, you're right. This is the problem. Good catch! However, I would suggest removing the reference to the Context from Position and just initialize the ImageView with it. The fewer the references to a Context, the better.

hazard1994 Over a year ago

m1ntf4n: It wont let me, the singlePlayerActivity isnt able to see the buttons. thanks for the help anyway

m1ntf4n Over a year ago

Glad I could help. Always be aware that any initialization you do outside the constructor will actually be copied to the beginning of each constructor (but after a super()call, if I'm not mistaken).

hazard1994 Over a year ago

dmon: Ive tried this before, but I couldnt find a valid context to use when creating the imageView

hazard1994 Over a year ago

M1ntf4n: here are the first few lines of code: ' public void onCreate(Bundle savedInstantState){ super.onCreate(savedInstantState); setContentView(R.layout.singleplayer); Player humanPlayer = new Player(); final Position[][] board = new Position[8][8]; Log.d("random Int",String.valueOf(whoPlaysFirst)); playerName=getPlayerName(humanPlayer); Piece piece = new Piece(); if(whoPlaysFirst == 1){ playerTurn = true; } else if(whoPlaysFirst == 0){ playerTurn = false; } setupBoard(board);'

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