android - How to draw a Rectangle on a 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="#ffffff"     >     <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 Rectangle"         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; import android.graphics.Rect;   public class MainActivity extends AppCompatActivity {     private Context mContext;     private Resources mResources;     private RelativeLayout mRelativeLayout;     private TextView mTextView;     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 to the canvas background                 canvas.drawColor(Color.LTGRAY);                  // Initialize a new Paint instance to draw the Rectangle                 Paint paint = new Paint();                 paint.setStyle(Paint.Style.FILL);                 paint.setColor(Color.YELLOW);                 paint.setAntiAlias(true);                  // Set a pixels value to padding around the rectangle                 int padding = 50;                  /*                     public Rect (int left, int top, int right, int bottom)                         Create a new rectangle with the specified coordinates. Note: no range                         checking is performed, so the caller must ensure that left <= right and                         top <= bottom.                      Parameters                         left : The X coordinate of the left side of the rectangle                         top : The Y coordinate of the top of the rectangle                         right : The X coordinate of the right side of the rectangle                         bottom : The Y coordinate of the bottom of the rectangle                  */                  // Initialize a new Rect object                 Rect rectangle = new Rect(                         padding, // Left                         padding, // Top                         canvas.getWidth() - padding, // Right                         canvas.getHeight() - padding // Bottom                 );                  /*                     public void drawRect (Rect r, Paint paint)                         Draw the specified Rect using the specified Paint. The rectangle will be                         filled or framed based on the Style in the paint.                      Parameters                         r : The rectangle to be drawn.                         paint : The paint used to draw the rectangle                 */                  // Finally, draw the rectangle on the canvas                 canvas.drawRect(rectangle,paint);                  // Display the newly created bitmap on app interface                 mImageView.setImageBitmap(bitmap);             }         });     } }
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