android - How to draw a Line on 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.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(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 on the canvas as background
canvas.drawColor(Color.LTGRAY);

// Initialize a new Paint instance to draw the line
Paint paint = new Paint();
// Line color
paint.setColor(Color.parseColor("#676767"));
paint.setStyle(Paint.Style.STROKE);
// Line width in pixels
paint.setStrokeWidth(12);
paint.setAntiAlias(true);

// Set a pixels value to offset the line from canvas edge
int offset = 50;

// Draw a line on canvas at the center position
canvas.drawLine(
offset, // startX
(float) canvas.getHeight() / 2, // startY
canvas.getWidth() - offset, // stopX
(float) canvas.getHeight() / 2, // stopY
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 Line"
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>