how to draw a circle on Canvas using java for android

Question

I want to draw a circle on a canvas in my android app. I searched a lot and realized if I need a dynamic form of painting which can be updated time by time I need to use canvas instead of imageView.

any help is appreciated

this is the code that I wrote so far but it will not draw anything on the android device screen:

    private void createBitMap() {
    Bitmap bitMap = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);  //creates bmp
    bitMap = bitMap.copy(bitMap.getConfig(), true);     //lets bmp to be mutable
    Canvas canvas = new Canvas(bitMap);                 //draw a canvas in defined bmp

    Paint paint = new Paint();                          //define paint and paint color
    paint.setColor(Color.RED);
    paint.setStyle(Style.FILL_AND_STROKE);
    //paint.setAntiAlias(true);

    canvas.drawCircle(50, 50, 10, paint);
}

possible dup: http://stackoverflow.com/questions/17954596/how-to-draw-circle-by-canvas-in-android — John, Dec 19 '13 at 03:38
simply use: protected void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.drawCircle(x, y, radius, paint); } — Shailendra Madda, Dec 19 '13 at 04:49

score 10 · Accepted Answer · answered Dec 19 '13 at 04:17

Update your createBitMap method like this

private void createBitMap() {
        // Create a mutable bitmap
        Bitmap bitMap = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);

        bitMap = bitMap.copy(bitMap.getConfig(), true);
        // Construct a canvas with the specified bitmap to draw into
        Canvas canvas = new Canvas(bitMap);
        // Create a new paint with default settings.
        Paint paint = new Paint();
        // smooths out the edges of what is being drawn
        paint.setAntiAlias(true);
        // set color
        paint.setColor(Color.BLACK);
        // set style
        paint.setStyle(Paint.Style.STROKE);
        // set stroke
        paint.setStrokeWidth(4.5f);
        // draw circle with radius 30
        canvas.drawCircle(50, 50, 30, paint);
        // set on ImageView or any other view 
        imageView.setImageBitmap(bitMap);

    }

Thanks a lot. It works. You showed me that I have to use ImageView and set the image in it. Thanks in advance — Hossein Dolatabadi, Dec 19 '13 at 05:01

score 2 · Answer 2 · edited Apr 24 '18 at 14:53

try this

create ImageView and use image.setImageBitmap(bitMap); to make a bitmap to visible.

public class MainActivity extends Activity { ImageView image;

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        image=(ImageView)findViewById(R.id.imageView1);
        createBitMap();
    }

    private void createBitMap() {
        Bitmap bitMap = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);  //creates bmp
        bitMap = bitMap.copy(bitMap.getConfig(), true);     //lets bmp to be mutable
        Canvas canvas = new Canvas(bitMap);                 //draw a canvas in defined bmp

        Paint paint = new Paint();
        // smooths
       paint.setAntiAlias(true);
        paint.setColor(Color.RED);
       paint.setStyle(Paint.Style.STROKE); 
        paint.setStrokeWidth(4.5f);
        // opacity
        //p.setAlpha(0x80); //
        canvas.drawCircle(50, 50, 30, paint);
        image.setImageBitmap(bitMap);
    }

thanks for your reply. I just want to change my own code so that I can draw the circle. Changing the whole means read every thing from the beginning :) — Hossein Dolatabadi, Dec 19 '13 at 03:51

how to draw a circle on Canvas using java for android

2 Answers2