定制视图与触摸事件——挑战练习：设备旋转问题

此问题是《Android编程权威指南》的第29章的29.5小节挑战练习：设备旋转问题。

从书本提示中可看出，要解决设备旋转后，绘制的矩形框会消失，需要注意的几点：
1.重写View的以下方法,用来保存数据和恢复数据：

protected Parcelable onSaveInstanceState()protected Parcelable onRestoreInstanceState(Parcelable state)

2.View视图要有ID,只有这样，上面两个方法才会被调用：

<?xml version="1.0" encoding="utf-8"?><com.example.administrator.boxdrawingview.BoxDrawingView    xmlns:android="http://schemas.android.com/apk/res/android"    **android:id="@+id/box_drawing_view"**    android:layout_width="match_parent"    android:layout_height="match_parent"   ></com.example.administrator.boxdrawingview.BoxDrawingView>

3.因为实现Parcelable比较繁琐，用Bundle保存状态数据。

4.需要保存View父视图的状态，在Bundle中保存super.onSaveInstanceState()方法结果，然后调用 super.onRestoreInstanceState(state)把结果发送给超类。

整个实现，BoxDrawingView.java文件为：

public class BoxDrawingView extends View {    private static final String TAG = "BoxDrawingView";    private Box mCurrentBox;    private Paint mBoxPaint;    private Paint mBackgroundPaint;    // 定制视图的List    private List<Box> mBoxen = new ArrayList<>();    // 保存状态数据，用Bundle    private Bundle saveStateBundle;//    1.使用View的以下方法,用来保存数据和恢复数据：//    protected Parcelable onSaveInstanceState()//    protected Parcelable onRestoreInstanceState(Parcelable state)    @Override    protected Parcelable onSaveInstanceState() {        saveStateBundle = new Bundle();        // 在Bundle中保存父视图状态，恢复状态时会将此发送给超类        saveStateBundle.putParcelable("onSaveInstanceState", super.onSaveInstanceState());        // 保存当前的状态数据，bundle保存List<Object>,强转Serializable        saveStateBundle.putSerializable("mBoxen", (Serializable) mBoxen);        return saveStateBundle;    }    @Override    protected void onRestoreInstanceState(Parcelable state) {        Bundle bundle = (Bundle) state;        // 将父视图状态取出，发送给超类        Parcelable restoreState = bundle.getParcelable("onSaveInstanceState");        super.onRestoreInstanceState(restoreState);        // 恢复状态数据        mBoxen = (List<Box>) bundle.getSerializable("mBoxen");    }    public BoxDrawingView(Context context) {        super(context);    }    public BoxDrawingView(Context context, AttributeSet attrs) {        super(context, attrs);        mBoxPaint = new Paint();        mBoxPaint.setColor(0x22ff0000);        mBackgroundPaint = new Paint();        mBackgroundPaint.setColor(0xfff8efe0);    }    @Override    public boolean onTouchEvent(MotionEvent event) {        PointF current = new PointF(event.getX(), event.getY());        String action = "";        switch (event.getAction()) {            case MotionEvent.ACTION_DOWN:                action = "ACTION_DOWN";                mCurrentBox = new Box(current);                mBoxen.add(mCurrentBox);                break;            case MotionEvent.ACTION_MOVE:                action = "ACTION_MOVE";                if (mCurrentBox != null) {                    mCurrentBox.setCurrent(current);                    invalidate();                }                break;            case MotionEvent.ACTION_UP:                action = "ACTION_UP";                mCurrentBox = null;                break;            case MotionEvent.ACTION_CANCEL:                action = "ACTION_CANCEL";                mCurrentBox = null;                break;        }        Log.i(TAG, action + "at x=" + current.x + ", y=" + current.y);        return true;    }    @Override    protected void onDraw(Canvas canvas) {        canvas.drawPaint(mBackgroundPaint);        for (Box box : mBoxen) {            float left = Math.min(box.getOrigin().x, box.getCurrent().x);            float right = Math.max(box.getOrigin().x, box.getCurrent().x);            float top = Math.min(box.getOrigin().y, box.getCurrent().y);            float bottom = Math.max(box.getOrigin().y, box.getCurrent().y);            canvas.drawRect(left, top, right, bottom, mBoxPaint);        }    }}