Changing object in Activity from a Class

Question

I have an Activity that has two objects of different classes.

I have a CanvasLayout class that needs to change the activity's objects upon certain conditions.

How do I do this?

CurrentlyCountingActivity

public class CurrentlyCountingActivity extends AppCompatActivity {

    CanvasLayout canvasLayout;

    //I want to call one of the carCommands and 
    //pathCoordinates functions from canvasLayout
    CarCommands carCommands;
    PathCoordinates pathCoordinates;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        canvasLayout = new CanvasLayout(this);
        setContentView(canvasLayout);
        carCommands = new CarCommands();

        //because I don't want the car to be moving initially
        carCommands.setAbsoluteSpeed(0, 0);
    }

    //Other functions dealing with Path coordinates
}

CanvasLayout class

public class CanvasLayout extends SurfaceView implements Runnable {

    ... initializations here

    @Override
    public void run() {

        prepBrush();

        while(canDraw) {
            ..other irrelevant code

            motionPoint();

            ...more code


            if((pointX == INITIAL_X) && (pointY == INITIAL_Y)) {
                canDraw = false;
                //I would like to have something like 
                //carCommands.setAbsoluteSpeed(0, 0); here
            }
        }
    }


   private void motionPoint() {
       //I want to call pathCoordinates of Activity in CanvasLayout
       pathCoordinates.trackPathCoordinates();
       pointX = pathCoordinates.getX();
       pointY = pathCoordinates.getY();

   }

}

Answer 1

Use Interface .

SurfaceView

private OnCanvasListener onCanvasListener;
public class CanvasLayout extends SurfaceView implements Runnable {

  public interface OnCanvasListener{

    public void doSomething();
   }

   public CanvasLayout(Context this){
onCanvasListener = (OnCanvasListener)this;
   }


 @Override
    public void run() {

        prepBrush();

        while(canDraw) {
            ..other irrelevant code

            motionPoint();

            ...more code


            if((pointX == INITIAL_X) && (pointY == INITIAL_Y)) {
                canDraw = false;
                //I would like to have something like 
                //carCommands.setAbsoluteSpeed(0, 0); here
                 onCanvasListener.doSomething(); // invoke interface method

            }
        }
    }

}

Implement interface in activity

public class CurrentlyCountingActivity extends AppCompatActivity implements OnCanvasListener  {

    CanvasLayout canvasLayout;

    //I want to call one of the carCommands and 
    //pathCoordinates functions from canvasLayout
    CarCommands carCommands;
    PathCoordinates pathCoordinates;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        canvasLayout = new CanvasLayout(this);
        setContentView(canvasLayout);
        carCommands = new CarCommands();

        //because I don't want the car to be moving initially
        carCommands.setAbsoluteSpeed(0, 0);
    }

    //Other functions dealing with Path coordinates

  @Override
public void doSomething(){

// implement your logic here.
}

}

Sorry for any typo . hope this will help.

Answer 2

There are several ways to provide access to the CarCommands object:

1. Create a constructor in CanvasLayout which takes a CarCommands object.

2. Create a setter method in CanvasLayout which takes a CarCommands object.

3. Create the CarCommands object in CanvasLayout.

4. Add methods to the activity class which allow access to the CarCommands object and add a constructor to CanvasLayout that accepts a CurrentlyCountingActivity.

I am sure there are other options as well. Which one you choose depends heavily on other factors in the design of your code. I learn towards #3. Does the activity really need the CarCommands?

I suggest that you continue to learn about object oriented principles. Only experience will help you judge the tradeoffs for design decisions such as this.