drawing a circle where the user has touched on canvas

问题

Starting to learn Canvas and have two classes so far (main one to call the view and the view) The View class onDraw creates a target (ie number of cicles and each one coloured differently)

I have a ontouch listenerer set up to record the x and y where the user clicks

my trouble then is drawing a new circle / point where the user touches

UPDATED with classes

Main Class

public class StartScreen extends Activity {

    DrawView drawView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        drawView = new DrawView(this);
        drawView.setBackgroundColor(Color.WHITE);
        setContentView(drawView);
}

Draw Class

public class DrawView extends View implements View.OnTouchListener {

    private Paint paint[];

    private Context context;
    private Canvas canvas;

    //definging some variables

    public DrawView(Context pContext) {
        super(pContext);  
        this.context = pContext;

        WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        Display display = wm.getDefaultDisplay();

        paint = new Paint[5];
        setupColours();

    // setting varibale like raduis etc



    }

    private void setupColours() {

        // Creating Arrray of Paint Colours

    }

    @Override
    public void onDraw(Canvas pCanvas) {

        canvas = pCanvas;

        newRadius = radius;

        for (int i = 0; i < rings; i++) {


            if (i == 3) {
                canvas.drawCircle(centreWidth, centreHeight, newRadius, paint[0]);
            } else {
                canvas.drawCircle(centreWidth, centreHeight, newRadius, paint[1]);
            }


            canvas.drawCircle(centreWidth, centreHeight, newRadius - targetBoundary, paint[i / 2]);

            newRadius = newRadius - ringOffset;

        }

        this.setOnTouchListener(this);

    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        Log.d("TAG2", "x: " + event.getX() + " y: " + event.getY());
        drawHit(event.getX(), event.getY());
        return true;
    }

    public void drawHit(float hitX, float hitY) {
        Log.d("HIT", "Hit being drawn");

        Paint paint2 = new Paint();
        paint2.setColor(Color.BLACK);

        canvas.drawCircle(hitX, hitY, 100, paint2);

    }

The method is called but the circle is not being drawn. what am I doing wrong. Thanks

回答1:

You have provided very little information in your question. A little elaboration wouldn't have hurt. Are the targets(the circles) being created as you would want them to be? If yes, then get a hold of the FrameLayout and use the 'addView' method to overlay your ball onto the main view.

A slightly old but nevertheless a tutorial which may be useful to you: http://www.kellbot.com/2009/06/android-hello-circle/

Good Luck

回答2:

https://github.com/swapgo20/Android-Hand-Drawing
https://github.com/codepath/android_guides/wiki/Basic-Painting-with-Views
https://github.com/Korilakkuma/CanvasView

I hope above link are very useful to draw shapes on canvas.

来源：https://stackoverflow.com/questions/11328848/drawing-a-circle-where-the-user-has-touched-on-canvas

标签

android

canvas