Tuesday, November 17, 2015

android - How to draw a circle on a Canvas

MainActivity.java

package com.cfsuman.androidtutorials;

import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;


public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Get the widgets reference from XML layout
        Button button = findViewById(R.id.button);
        ImageView imageView = findViewById(R.id.imageView);


        // Set a click listener for Button widget
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // Initialize a new Bitmap object
                Bitmap bitmap = Bitmap.createBitmap(
                        1200, // Width
                        600, // Height
                        Bitmap.Config.ARGB_8888 // Config
                );

                // Initialize a new Canvas instance
                Canvas canvas = new Canvas(bitmap);

                // Draw a solid color to the canvas background
                canvas.drawColor(Color.LTGRAY);

                // Initialize a new Paint instance to draw the Circle
                Paint paint = new Paint();
                paint.setStyle(Paint.Style.FILL);
                paint.setColor(Color.RED);
                paint.setAntiAlias(true);

                // Calculate the available radius of canvas
                int radius = Math.min(
                        canvas.getWidth(),canvas.getHeight()/2);

                // Set a pixels value to padding around the circle
                int padding = 5;

                // Finally, draw the circle on the canvas
                canvas.drawCircle(
                        (float)canvas.getWidth() / 2, // cx
                        (float)canvas.getHeight() / 2, // cy
                        radius - padding, // Radius
                        paint // Paint
                );

                // Display the newly created bitmap on app interface
                imageView.setImageBitmap(bitmap);
            }
        });
    }
}
activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#DCDCDC"
    android:padding="24dp">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Draw Circle"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button" />

</androidx.constraintlayout.widget.ConstraintLayout>