Examples of basic usage of drawing canvas for Android programming

package ;
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public class MainActivity extends Activity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    (savedInstanceState);
    //Instantiate GraphicsView    GraphicsView gv = new GraphicsView(this);
    /* In the past we displayed the layout file through setContentView(.activity_main)
      * In this example, use the GraphicsView object gv instead of the previous layout file
      */
    setContentView(gv);
  }
}

package ;
import ;
import ;
import ;
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public class GraphicsView extends View{
  //Declare the brush  Paint paint=null;
  public GraphicsView(Context context) {
    super(context);
    /*----------------------------------------------
      * In some books, Paint paint=new Paint(); is placed in the onDraw method. It is recommended that
      * Try not to put the initialization brush in the onDraw method, this is because onDraw often runs
      * If you arrive, don't use new objects in it, the fewer the better, otherwise it will waste memory
      *---------------------------------------------*/
    //Get the brush and initialize the brush    paint=new Paint();
  }
  @Override
  protected void onDraw(Canvas canvas){
    //Set the canvas background to white    ();
    //Set the brush to red    ();
    // Use the current brush to draw a rectangle with the upper left coordinates of 80,20 and the lower right coordinates of 360,180    (80,20,360,180, paint);
    //Set the brush to green    ();
    // Use the current brush to draw a circle with a center coordinate of 220,100 and a radius of 60    (220,100, 60, paint);
  }
}