How to draw circle by canvas in Android

Question

I want to draw circle by canvas  Here is my code   MyActivity java   public class MyActivity extends Activity     public void onCreate Bundle savedInstanceState                        setContentView new View this w h                      View java   public class View extends SurfaceView       public View Context context  int w  int h                super context           Canvas grid   new Canvas Bitmap createBitmap h w  Bitmap Config ARGB 8888            grid  drawColor Color WHITE           Paint paint   new Paint            paint setStyle Paint Style FILL           grid drawCircle w 2  h 2   w 2  paint            So I have just black screen without circle  Why it does not work  How to fix it

User · Answer

If you are using your own CustomView extending View class, you need to call canvas.invalidate() method which will internally call onDraw method. You can use default API for canvas to draw a circle. The x, y cordinate define the center of the circle. You can also define color and styling in paint & pass the paint object.

public class CustomView extends View {

    public CustomView(Context context,  AttributeSet attrs) {
        super(context, attrs);
        setupPaint();
    }
}

Define default paint settings and canvas (Initialise paint in constructor so that you can reuse the same object everywhere and change only specific settings wherever required)

private Paint drawPaint;

// Setup paint with color and stroke styles
private void setupPaint() {
    drawPaint = new Paint();
    drawPaint.setColor(Color.BLUE);
    drawPaint.setAntiAlias(true);
    drawPaint.setStrokeWidth(5);
    drawPaint.setStyle(Paint.Style.FILL_AND_STROKE);
    drawPaint.setStrokeJoin(Paint.Join.ROUND);
    drawPaint.setStrokeCap(Paint.Cap.ROUND);
}

And initialise canvas object

private Canvas canvas;

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    this.canvas = canvas;
    canvas.drawCircle(xCordinate, yCordinate, RADIUS, drawPaint);
}

And finally, for every view refresh or new draw on the screen, you need to call invalidate method. Remember your entire view is redrawn, hence this is an expensive call. Make sure you do only the necessary operations in onDraw

canvas.invalidate();

For more details on canvas drawing refer https://medium.com/@mayuri.k18/android-canvas-for-drawing-and-custom-views-e1a3e90d468b

User · Answer

public class CircleView extends View        private static final String COLOR HEX     E74300       private final Paint drawPaint      private       float size       public CircleView final Context context  final AttributeSet attrs            super context  attrs           drawPaint   new Paint            drawPaint setColor Color parseColor COLOR HEX            drawPaint setAntiAlias true           setOnMeasureCallback                Override     protected void onDraw final Canvas canvas            super onDraw canvas           canvas drawCircle size  size  size  drawPaint              private void setOnMeasureCallback             ViewTreeObserver vto   getViewTreeObserver            vto addOnGlobalLayoutListener new ViewTreeObserver OnGlobalLayoutListener                  Override             public void onGlobalLayout                     removeOnGlobalLayoutListener this                   size   getMeasuredWidth     2                                        TargetApi Build VERSION CODES JELLY BEAN      private void removeOnGlobalLayoutListener ViewTreeObserver OnGlobalLayoutListener listener            if  Build VERSION SDK INT  lt  16                getViewTreeObserver   removeGlobalOnLayoutListener listener             else               getViewTreeObserver   removeOnGlobalLayoutListener listener                       Xml example  will produce a circle of 5dp    lt com example CircleView         android layout width  10dp          android layout height  10dp   gt

User · Answer

Try this     The entire code for drawing a circle or download project source code and test it on your android studio  Draw circle on canvas programmatically    import android graphics Bitmap      import android graphics Canvas      import android graphics Color      import android graphics Paint      import android graphics Path      import android graphics Point      import android graphics PorterDuff      import android graphics PorterDuffXfermode      import android graphics Rect      import android graphics RectF      import android widget ImageView            public class Shape                private Bitmap bmp              private ImageView img              public Shape Bitmap bmp  ImageView img                     this bmp bmp                  this img img                  onDraw                               private void onDraw                     Canvas canvas new Canvas                     if  bmp getWidth      0    bmp getHeight      0                         return                                     int w   bmp getWidth    h   bmp getHeight                     Bitmap roundBitmap   getRoundedCroppedBitmap bmp  w                    img setImageBitmap roundBitmap                               public static Bitmap getRoundedCroppedBitmap Bitmap bitmap  int radius                    Bitmap finalBitmap                  if  bitmap getWidth      radius    bitmap getHeight      radius                      finalBitmap   Bitmap createScaledBitmap bitmap  radius  radius                              false                   else                     finalBitmap   bitmap                  Bitmap output   Bitmap createBitmap finalBitmap getWidth                            finalBitmap getHeight    Bitmap Config ARGB 8888                   Canvas canvas   new Canvas output                    final Paint paint   new Paint                    final Rect rect   new Rect 0  0  finalBitmap getWidth                            finalBitmap getHeight                      paint setAntiAlias true                   paint setFilterBitmap true                   paint setDither true                   canvas drawARGB 0  0  0  0                   paint setColor Color parseColor   BAB399                     canvas drawCircle finalBitmap getWidth     2   0 7f  finalBitmap getHeight     2   0 7f  finalBitmap getWidth     2   0 1f  paint                   paint setXfermode new PorterDuffXfermode PorterDuff Mode SRC IN                    canvas drawBitmap finalBitmap  rect  rect  paint                    return output

User · Answer

Override public void onDraw Canvas canvas       canvas drawCircle xPos  yPos radius  paint       Above is the code to render a circle  Tweak the parameters to your suiting

User · Answer

Here is example to draw stroke circle canvas  val paint   Paint   apply       color   Color RED     style   Paint Style STROKE     strokeWidth   10f    override fun onDraw canvas  Canvas         super onDraw canvas      canvas  drawCircle 200f  100f  100f  paint      Result    Example to draw solid circle canvas  val paint   Paint   apply       color   Color RED    override fun onDraw canvas  Canvas         super onDraw canvas      canvas  drawCircle 200f  100f  100f  paint      Result    Hope it help

User · Answer

private Paint green   new Paint         private int greenx   greeny     green setColor Color GREEN            green setAntiAlias false            canvas drawCircle greenx greeny 20 green

User · Answer

You can override the onDraw method of your view and draw the circle   protected void onDraw Canvas canvas     super onDraw canvas     canvas drawCircle x  y  radius  paint        For a better reference on drawing custom views check out the official Android documentation   http   developer android com training custom-views custom-drawing html

User · Answer

import android app Activity  import android content Context  import android graphics Canvas  import android graphics Color  import android graphics Paint  import android os Bundle  import android view View   public class MainActivity extends Activity           Override      public void onCreate Bundle savedInstanceState                  super onCreate savedInstanceState            setContentView new MyView this                 public class MyView extends View                 Paint paint   null           public MyView Context context                            super context                 paint   new Paint                          Override          protected void onDraw Canvas canvas                          super onDraw canvas               int x   getWidth                int y   getHeight                int radius              radius   100              paint setStyle Paint Style FILL               paint setColor Color WHITE               canvas drawPaint paint                  Use Color parseColor to define HTML colors             paint setColor Color parseColor   CD5C5C                 canvas drawCircle x   2  y   2  radius  paint                        Edit if you want to draw circle at centre  You could also translate your entire canvas to center then draw circle at center using   canvas translate getWidth   2f getHeight   2f   canvas drawCircle 0 0  radius  paint     These two link also help  http   www compiletimeerror com 2013 09 introduction-to-2d-drawing-in-android html  VIg A5SSy9o  http   android-coding blogspot com 2012 04 draw-circle-on-canvas-canvasdrawcirclet html

[java] How to draw circle by canvas in Android?

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