Android中view的简单应用---随手指移动的小球

public class DrawView extends View{     public  float currentX=40;     public float currentY=50;     public DrawView(Context context){         super(context);     }     //重写ondraw,通过canvas绘画     protected void onDraw(Canvas canvas){         Paint paint=new Paint();         paint.setColor(Color.RED);         canvas.drawCircle(currentX,currentY,25,paint);     }

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     android:orientation="vertical"     android:background="#99FFCC"     android:id="@+id/root"> </LinearLayout>

public class MainActivity extends Activity{     @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         LinearLayout root=(LinearLayout) findViewById(R.id.root);         final DrawView drawView=new DrawView(this);         WindowManager wm = this.getWindowManager();         int width = wm.getDefaultDisplay().getWidth();         int height = wm.getDefaultDisplay().getHeight();         Toast.makeText(this,"width is"+width+"height"+height,Toast.LENGTH_LONG).show();         drawView.setMinimumHeight(300);         drawView.setMinimumHeight(500);         drawView.setOnTouchListener(new View.OnTouchListener(){             @Override             public boolean onTouch(View v, MotionEvent event) {                 drawView.currentX=event.getX();                 drawView.currentY=event.getY();                 drawView.invalidate();                 return  true;             }         });             root.addView(drawView);     } }