Question

While trying to calculate the function between a touch point (dx, dy), i am receiving an error when calling the calculation function.

Here is my move function:

public class Mice {

public Movement getRatio;
public static float MX;
public static float MY;

public Mice(float x, float y){
    MX = x;
    MY = y;
}

public void move(float dx, float dy){
    float[] ratio = new float[2];
    //below this comment is my error:
    ratio = getRatio.getPath(dx, dy, MX, MY);
    MX++;
    MY = MY + ratio[1];
    GameActivity.mpx = MX;
    GameActivity.mpy = MY;
}

}

(MX, MY) is another point where an object is right now on the screen.

Here is my calculation function:

public class Movement {

public float[] getPath(float dx, float dy, float mX, float mY){
    float[] ratio = new float[2];
    ratio[0] = 1;
    float a;
    float Ry1;
    float Ry2;
    float Rx1 = 1;
    float Rx2 = 2;
    a = (dy-mY)/(dx-mX);
    Ry1=a*(Rx1-dx)+dy;
    Ry2=a*(Rx2-dx)+dy;
    ratio[1] = Math.abs(Ry1-Ry2);

    return ratio;
}

}

My onTouchEvent

@Override
public boolean onTouchEvent(MotionEvent event){

dx = event.getX();
dy = event.getY();


if(event.getAction()==1){
thread = new MiceThread(mice, mview, dx, dy);
thread.start();
}

return true;
}

And here is my thread:

public class MiceThread extends Thread {

private Mice gameMice;
private MiceView gameView;
private float x;
private float y;

public MiceThread(Mice theMice, MiceView theView, float x, float y){
    this.gameMice = theMice;
    this.gameView = theView;
    this.x = x;
    this.y = y;
}

public void run(){
    while(1<2){
        this.gameMice.move(x, y);
        this.gameView.postInvalidate();

        try
        {
            MiceThread.sleep(5);

        }
        catch (InterruptedException e)
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

}

I am getting the error where specified in the first block of code.

Thanks!

Answer 1

if you get a Null Pointer , I see you never initialized your Movement getRatio

add it to your Constructor:

public Mice(float x, float y){
MX = x;
MY = y;
getRatio = new Movement();
}

and Fill in any parameter you need for your Movement…

You Can also make a static Method inside your Movement like this:

public class Movement {

    public static float[] getPath(float dx, float dy, float mX, float mY){
       ...
    }
}

and use it like this:

public void move(float dx, float dy){
    float[] ratio = Movement.getPath(dx, dy, MX, MY);
    MX++;
    MY = MY + ratio[1];
    GameActivity.mpx = MX;
    GameActivity.mpy = MY;
}

your getPath(...) function has nothing to do with it.

EDIT:

Cannot Really help, because the lack of info. Only a few Notes…

AVOID

if(event.getAction()==1){
  thread = new MiceThread(mice, mview, dx, dy);
  thread.start();
}

Try it like

if(event.getAction()==1){
    if (thread =! null){
        //kill Thread First. instead of while(1<2) add a boolean inside MiceThread.run 
        // and set it to false at this point.... 
        // if you don't this Thread may live as long as GC doesn't kill it.
    }
    thread = new MiceThread(mice, mview, dx, dy);
    thread.start();
}

Then

public void run(){
while(someBool){
    this.gameMice.move(x, y);
    //does your Mice View has a reference to this.gameMice???
    //if not update your Mice inside this.gameView....
    // I Cannot tell you how, because I don't know what MiceView is doing...
    //postInvalidate() works ONLY, if Something inside the VIEW had changed...
    this.gameView.postInvalidate();

    try
    {
        MiceThread.sleep(5);

    }
    catch (InterruptedException e)
    {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}
}