自定义View （不应写布局）

• Pview.java

public class Pview extends View {

    private int cirx = 20, ciry = 20; // 圆心点
    private int radius = 20; // 半径
    private int rectx = 100, recty = 400;
    private int dirx, diry; // 方向0正方向 ， 1反方向
    private Timer mTimer = new Timer(); // 定时器
    private int width, height;
    private Paint mPaint;

    //布局发生变化时的回调函数，间接回去调用onMeasure, onLayout函数重新布局 
    @Override
    protected void onSizeChanged(int w, int h, int oldl, int oldt) {
        super.onSizeChanged(w, h, oldl, oldt);
        width = w;
        height = h;
    }

    public Pview(Context context) {
        super(context);
        // 设置聚焦
        setFocusable(true);
        // 图形的绘制，运动方向
        // 自由任务交给定时任务去做
        TimerTask mTask = new TimerTask() {

            @Override
            public void run() {
                // 绘制圆的运动方向（自由匀速）
                if (dirx == 0) {
                    cirx += 5;
                }
                if (dirx == 1) {
                    cirx -= 5;
                }
                if (diry == 0) {
                    ciry += 5;
                }
                if (diry == 1) {
                    ciry -= 5;
                }
                // 修改运动方向
                // 最右边
                if (cirx + radius > width) {
                    dirx = 1;
                }
                // 最左边
                if (cirx - radius < 0) {
                    dirx = 0;
                }
                // 最下边
                if (ciry + radius > height) {
                    diry = 1;
                }
                // 最上边
                if (ciry - radius < 0) {
                    diry = 0;
                }
                // 球碰到矩形也要更改方向
                if (cirx > rectx && cirx < rectx + 300) {
                    if (ciry + radius > recty) {
                        diry = 1;// 往上走
                    }
//                  if (ciry - radius < recty) {
//                      diry = 0;// 往下走
//                  }
                }
                postInvalidate();// 进行实时刷新
            }
        };
        // 把任务加到计时器里面去
        mTimer.schedule(mTask, 1, 20);
    }

        // 绘制图形
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        mPaint = new Paint();
        mPaint.setColor(Color.RED);
        canvas.drawCircle(cirx, ciry, radius, mPaint);// 画圆

        mPaint.setColor(Color.BLACK);
        canvas.drawRect(rectx, recty, rectx + 300, recty + 2, mPaint);// 画矩形
    }

    //控制板上下移动
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {

        switch (keyCode) {
        case KeyEvent.KEYCODE_DPAD_DOWN:
            recty+=15;
            break;
        case KeyEvent.KEYCODE_DPAD_UP:
            recty-=15;
            break;
        case KeyEvent.KEYCODE_DPAD_LEFT:
            rectx-=15;
            break;
        case KeyEvent.KEYCODE_DPAD_RIGHT:
            rectx+=15;
            break;

        default:
            break;
        }
        return true;
    }
}

• MainActivity.java(引用View)

public class MainActivity extends Activity {

    private Pview mPview = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        mPview = new Pview(this);
        super.onCreate(savedInstanceState);
        // setContentView(R.layout.activity_main);
        setContentView(mPview);
        mPview.requestFocus();
    }
}

• 演示

action.gif