Android中View的滑动冲突——Android开发艺术探索笔记

介绍

相信开发Android的人都会有这种体会：从网上下载的demo运行的好好的，但是只要出现了滑动冲突，Demo就无法正常工作了。但是不用担心，解决滑动冲突有固定的模式，常见的有内部拦截和外部拦截两种，只要按照这个模式来就可以顺利解决。

常见的滑动冲突场景

示例

处理规则

对于场景1，处理规则为：当用户左右滑动时，让外部的View拦截点击事件，当用户上下滑动时，让内部的View拦截点击事件。当产生滑动时，根据滑动的起始点与终点坐标位置，如果垂直方向滑动距离大，就判断为垂直滑动，否则判断为水平滑动。其他两种情况处理方法相似，都是从业务需求上得出相应的规则。

解决方法

外部拦截发

所有的点击事件都先经过父容器拦截处理，如果父容器需要拦截就拦截，不需要就传给内部的View。伪代码如下

  public boolean onInterceptTouchEvent(MotionEvent event) {
        boolean intercepted = false;

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN: {
                intercepted = false;
                break;
            }
            case MotionEvent.ACTION_MOVE: {
                if (满足父容器的拦截要求) {
                    intercepted = true;
                } else {
                    intercepted = false;
                }
                break;
            }
            case MotionEvent.ACTION_UP: {
                intercepted = false;
                break;
            }
            default:
                break;
        }
        mLastXIntercept = x;
        mLastYIntercept = y;
        return intercepted;
    }

注：
ACTION_DOWN这个事件是不能拦截的，因为一旦拦截后续的事件都会由父容器处理了。

内部拦截法

父容器不拦截任何事件，所有事件都传给子元素。如果子元素需要此事件就直接消耗，否则就交给父容器进行处理。完成这个功能需要配合requestDisallowInterceptTouchEvent()方法才可。这个方法表示是否让父容器拦截事件。伪代码如下：

 public boolean dispatchTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();

        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN: {
            parent.requestDisallowInterceptTouchEvent(true);
            break;
        }
        case MotionEvent.ACTION_MOVE: {
            if (满足父容器的拦截要求) {
                parent.requestDisallowInterceptTouchEvent(false);
            }
            break;
        }
        case MotionEvent.ACTION_UP: {
            break;
        }
        default:
            break;
        }
        mLastX = x;
        mLastY = y;
        return super.dispatchTouchEvent(event);
    }

注
父容器默认拦截除了ACTION_DOWN以外的其他事件，这样子当元素调用parent.requestDisallowInterceptTouchEvent(false)时，父元素才能拦截所需的事件。

总结

示例效果的源码

Activity

public class DemoActivity_1 extends Activity {
    private static final String TAG = "DemoActivity_1";

    private HorizontalScrollViewEx mListContainer;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.demo_1);
        Log.d(TAG, "onCreate");
        initView();
    }

    private void initView() {
        LayoutInflater inflater = getLayoutInflater();
        mListContainer = (HorizontalScrollViewEx) findViewById(R.id.container);
        final int screenWidth = MyUtils.getScreenMetrics(this).widthPixels;
        final int screenHeight = MyUtils.getScreenMetrics(this).heightPixels;
        for (int i = 0; i < 3; i++) {
            ViewGroup layout = (ViewGroup) inflater.inflate(
                    R.layout.content_layout, mListContainer, false);
            layout.getLayoutParams().width = screenWidth;
            TextView textView = (TextView) layout.findViewById(R.id.title);
            textView.setText("page " + (i + 1));
            layout.setBackgroundColor(Color.rgb(255 / (i + 1), 255 / (i + 1), 0));
            createList(layout);
            mListContainer.addView(layout);
        }
    }

    private void createList(ViewGroup layout) {
        ListView listView = (ListView) layout.findViewById(R.id.list);
        ArrayList datas = new ArrayList();
        for (int i = 0; i < 50; i++) {
            datas.add("name " + i);
        }

        ArrayAdapter adapter = new ArrayAdapter(this,
                R.layout.content_list_item, R.id.name, datas);
        listView.setAdapter(adapter);
        listView.setOnItemClickListener(new OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView parent, View view,
                    int position, long id) {
                Toast.makeText(DemoActivity_1.this, "click item",
                        Toast.LENGTH_SHORT).show();

            }
        });
    }
}

水平滑动的View

public class HorizontalScrollViewEx extends ViewGroup {
    private static final String TAG = "HorizontalScrollViewEx";

    private int mChildrenSize;
    private int mChildWidth;
    private int mChildIndex;

    // 分别记录上次滑动的坐标
    private int mLastX = 0;
    private int mLastY = 0;
    // 分别记录上次滑动的坐标(onInterceptTouchEvent)
    private int mLastXIntercept = 0;
    private int mLastYIntercept = 0;

    private Scroller mScroller;
    private VelocityTracker mVelocityTracker;

    public HorizontalScrollViewEx(Context context) {
        super(context);
        init();
    }

    public HorizontalScrollViewEx(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public HorizontalScrollViewEx(Context context, AttributeSet attrs,
                                  int defStyle) {
        super(context, attrs, defStyle);
        init();
    }

    private void init() {
        mScroller = new Scroller(getContext());
        mVelocityTracker = VelocityTracker.obtain();
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        boolean intercepted = false;
        int x = (int) event.getX();
        int y = (int) event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN: {
                Log.d(TAG, "onInterceptTouchEvent: ACTION_DOWN");
                intercepted = false;
                if (!mScroller.isFinished()) {
                    mScroller.abortAnimation();
                    intercepted = true;
                }
                break;
            }
            case MotionEvent.ACTION_MOVE: {
                Log.d(TAG, "onInterceptTouchEvent: ACTION_MOVE");
                int deltaX = x - mLastXIntercept;
                int deltaY = y - mLastYIntercept;
                if (Math.abs(deltaX) > Math.abs(deltaY)) {
                    intercepted = true;
                } else {
                    intercepted = false;
                }
                break;
            }
            case MotionEvent.ACTION_UP: {
                intercepted = false;
                break;
            }
            default:
                break;
        }

        Log.d(TAG, "intercepted=" + intercepted);