CODEWITHSUNDEEP
javaandroidanimationbitmapandroid-canvas
David
David

Reputation: 521

Move object in a circle from random location

This is about the third time I've asked a question like this. I've already read all the similar questions and the previous help was useful but this time I want to add a new feature to this app. I have an app that makes a ball move in a circle.

Now I want to place the ball at a random location on the screen and then move in a circle. I think I've got the logic mostly correct but the ball jumps around erratically - no matter how much I play with the math. Code is below.

Does anyone know what I'm doing wrong?

public class DrawingTheBall extends View {

Bitmap bball; 

int randX, randY;
double theta;


public DrawingTheBall(Context context) {
    super(context);
    // TODO Auto-generated constructor stub
    bball = BitmapFactory.decodeResource(getResources(), R.drawable.blueball);

    randX = 1 + (int)(Math.random()*500); 
    randY = 1 + (int)(Math.random()*500);
    theta = 45;
}

  public void onDraw(Canvas canvas){
    super.onDraw(canvas);

    Rect ourRect = new Rect();
    ourRect.set(0, 0, canvas.getWidth(), canvas.getHeight()/2);
    float a = 50;
    float b = 50;
    float r = 50;

    int x = 0;
    int y = 0;

    theta = theta + Math.toRadians(2);


    Paint blue = new Paint();
    blue.setColor(Color.BLUE);
    blue.setStyle(Paint.Style.FILL);

    canvas.drawRect(ourRect, blue);

    if(x < canvas.getWidth()){

        x = randX + (int) (a +r*Math.cos(theta));
    }else{
        x = 0;
    }
    if(y < canvas.getHeight()){

        y = randY + (int) (b +r*Math.sin(theta));
    }else{
        y = 0;
    }
    Paint p = new Paint();
    canvas.drawBitmap(bball, x, y, p);
    invalidate();
}

}

Upvotes: 0

Views: 563

Answers (1)

DevOfZot
DevOfZot

Reputation: 1392

Do you really mean to generate new random values for randX and randY on every pass trough onDraw()? If I understand you right, this bit should be moved in to the constructor:

int randX = 1 + (int)(Math.random()*500); 
int randY = 1 + (int)(Math.random()*500);

edit: Also, remove the "int"s as so:

randX = 1 + (int)(Math.random()*500); 
randY = 1 + (int)(Math.random()*500);

This way will assign values to your class-level variables instead of creating local variables (which never get read). If that doesn't make sense, here's a clearer explanation:

class foo {
    int x = 1;      // this is a class-level variable
    public foo() {
        bar1();
        System.out.println(x);  // result: 1
        bar2();
        System.out.println(x);  // result: 2
    }
    public void bar1() {
        int x = 2;  // This instantiated a new 
                    // local variable "x", it did not 
                    // affect the global variable "x"
    }
    public void bar2() {
        x = 2;      // This changed the class var
    }
}

Upvotes: 2

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