android - How to draw a Line on Canvas

activity_main.xml 
 <?xml version="1.0" encoding="utf-8"?> <RelativeLayout     xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:id="@+id/rl"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:padding="16dp"     tools:context=".MainActivity"     android:background="#e8f5e9"     >     <ImageView         android:id="@+id/iv"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         />     <Button         android:id="@+id/btn"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="Draw Line"         android:layout_alignParentRight="true"         android:layout_alignParentEnd="true"         android:layout_alignParentBottom="true"         /> </RelativeLayout>
MainActivity.java 
 package com.cfsuman.me.androidcode;  import android.content.Context; import android.content.res.Resources; import android.graphics.Color; import android.graphics.Paint; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.ImageView; import android.widget.RelativeLayout; import android.widget.TextView; import android.graphics.Canvas; import android.graphics.Bitmap;   public class MainActivity extends AppCompatActivity {     private Context mContext;     private Resources mResources;     private RelativeLayout mRelativeLayout;     private Button mButton;     private ImageView mImageView;      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          // Get the application context         mContext = getApplicationContext();          // Get the Resources         mResources = getResources();          // Get the widgets reference from XML layout         mRelativeLayout = (RelativeLayout) findViewById(R.id.rl);         mButton = (Button) findViewById(R.id.btn);         mImageView = (ImageView) findViewById(R.id.iv);          // Set a click listener for Button widget         mButton.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View view) {                 // Initialize a new Bitmap object                 Bitmap bitmap = Bitmap.createBitmap(                         500, // Width                         300, // 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.RED);                 paint.setStyle(Paint.Style.STROKE);                 // Line width in pixels                 paint.setStrokeWidth(8);                 paint.setAntiAlias(true);                  // Set a pixels value to offset the line from canvas edge                 int offset = 50;                  /*                     public void drawLine (float startX, float startY, float stopX, float stopY, Paint paint)                         Draw a line segment with the specified start and stop x,y coordinates, using                         the specified paint.                          Note that since a line is always "framed", the Style is ignored in the paint.                          Degenerate lines (length is 0) will not be drawn.                      Parameters                         startX : The x-coordinate of the start point of the line                         startY : The y-coordinate of the start point of the line                         paint : The paint used to draw the line                  */                  // Draw a line on canvas at the center position                 canvas.drawLine(                         offset, // startX                         canvas.getHeight() / 2, // startY                         canvas.getWidth() - offset, // stopX                         canvas.getHeight() / 2, // stopY                         paint // Paint                 );                  // Display the newly created bitmap on app interface                 mImageView.setImageBitmap(bitmap);             }         });     } }
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