最近在讀Android開發藝術探索,本文作為自己對view的滑動衝突的理解和實踐記錄

而滑動衝突,需要了解Android的事件分發機制,如果這個還有些疑惑的地方,請參考這篇文章,以及其中的參考文章

還需要View的Measure和Layout的相關知識View的Measure流程總結

自定義view注意

1.如果直接繼承view,此時wrap_content和使用match_parent效果一樣.需要在onMeasure()中處理AT_MOST條件,處理wrap_content.

2.margin要在onLayout中設定,padding需要在 onDraw中設定

3.重新整理回撥,停止縣城或者動畫 在view.onDetachedFromWindow

4.在dispatchTouchEvent和TouchEvent中處理好滑動事件.

滑動衝突的種類

場景一：外部和內部倆層滑動方向不一致

場景二：外部和內部倆層滑動方向一致

場景三：主要是針對場景一和二的巢狀

滑動處理千篇一律, 只要你找到什麼時候父控制元件滑動,什麼時候子空間滑動.然後再父佈局中,選擇 是否自己處理onInterceptTouchEvent(),就好了.

Android開發藝術探索中有兩種方式,分別為外部攔截髮,和內部攔截法.我上面說的是外部攔截法(感覺這個好用些).
具體的內容,大家可以看 Android開發藝術探索第三章第五節相關內容.

情形1的處理

先上效果圖

下面是自定義的view,解決了上述情景1的問題.

/**
    自定義滑動viewPager
 * Created by chenchangjun on 17/7/14.
 */

public class HorizontalScrollView extends ViewGroup {


    private static final String TAG = HorizontalScrollView.class.getSimpleName();


    private int mChildWidth = 1;
    private int mChildIndex = 1
 
;

    private int mLastX;
    private int mLastY;

    private int mLastXIntercept = 0;
    private int mLastYIntercept = 0;
    /**
     * Scroller只是個計算器,處理滑動效果的,例如ViewPager,listview等的內部類
     */
    private Scroller mScroller;
    /**
     * 速度獲取器
     */
    private VelocityTracker mVelocityTracker;
    private int mChildrenCount;


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

    }


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


        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                intercept = false;
                if (!mScroller.isFinished()) {
                    mScroller.abortAnimation();
                }
                break;
            case MotionEvent.ACTION_MOVE:
                int deltaX = x - mLastXIntercept;
                int deltaY = y - mLastYIntercept;
                if (Math.abs(deltaX) > Math.abs(deltaY)) {
                    intercept = true;
                } else {
                    intercept = false;
                }
                break;

            case MotionEvent.ACTION_UP:
                intercept = false;
                break;
            default:
                break;

        }
        Log.d(TAG, "intercept=" + intercept);

        mLastX = x;
        mLastY = y;
        mLastXIntercept = x;
        mLastYIntercept = y;

        return intercept;

    }


    @Override
    public boolean onTouchEvent(MotionEvent event) {
        mVelocityTracker.addMovement(event);
        int x = (int) event.getX();
        int y = (int) event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                if (!mScroller.isFinished()) {
                    mScroller.abortAnimation();

                }

                break;

            case MotionEvent.ACTION_MOVE:
                int deltaX = x - mLastX;
                scrollBy(-deltaX, 0);//視覺上向右滑動,相對的,view橫向向左移動.
                break;

            case MotionEvent.ACTION_UP:

                int scrollX = getScrollX();
//                int srcollToChildIndex=scrollX/mChildWidth;
                mVelocityTracker.computeCurrentVelocity(1000);
                float xVelocity = mVelocityTracker.getXVelocity();
                if (Math.abs(xVelocity) >= 30) { //當一秒滑動畫素大於30畫素的時候,
                    mChildIndex = xVelocity > 0 ? mChildIndex - 1 : mChildIndex + 1;//計算pager下標mChildIndex.如果手指從右向左,則xVelocity為負,mChildIndex+1;反之,易然.
                } else {
                    mChildIndex = (scrollX + mChildWidth / 2) / mChildWidth;

                }
                int dex=0;

               /* if (mChildIndex >= getChildCount()) {
                    mChildIndex = 0;
                } else if (mChildIndex < 0) {
                    mChildIndex = getChildCount() - 1;
                } else {
                    dex = mChildIndex * mChildWidth - scrollX;

                }*/
                mChildIndex=Math.max(0,Math.min(mChildIndex,mChildrenCount-1));
                dex = mChildIndex * mChildWidth - scrollX;

                smoothScrollBy(dex, 0);
                mVelocityTracker.clear();


                break;
            default:
                break;

        }


        mLastX = x;
        mLastY = y;
        return true;

    }

    private void smoothScrollBy(int dx, int dy) {
        mScroller.startScroll(getScrollX(), 0, dx, 0, 500);

        invalidate();
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int childLeft = 0;
        final int childCount = getChildCount();
        mChildrenCount = childCount;

        for (int i = 0; i < childCount; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() != GONE) {
                mChildWidth = child.getMeasuredWidth();
                child.layout(childLeft, 0, childLeft + child.getMeasuredWidth(), child.getMeasuredHeight());
                childLeft += mChildWidth;
            }
        }

    }


    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int measuredWidth = 0;
        int measuredHeight = 0;
        final int childCount = getChildCount();
        measureChildren(widthMeasureSpec, heightMeasureSpec);

        int widthSpaceSize = MeasureSpec.getSize(widthMeasureSpec);
        int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightSpaceSize = MeasureSpec.getSize(heightMeasureSpec);
        int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);

        if (childCount == 0) {
            setMeasuredDimension(0, 0);
        } else if (heightSpecMode == MeasureSpec.AT_MOST && widthSpecMode == MeasureSpec.AT_MOST) {
            final View childView = getChildAt(0);//因為這裡的child都是同類,所以偷懶~取第一個測量尺寸就夠啦
            measuredWidth = childView.getMeasuredWidth() * childCount;
            measuredHeight = childView.getMeasuredHeight() * childCount;
            setMeasuredDimension(measuredWidth, measuredHeight);
        } else if (heightSpecMode == MeasureSpec.AT_MOST) {
            final View childView = getChildAt(0);//因為這裡的child都是同類,所以偷懶~取第一個測量尺寸就夠啦
            measuredHeight = childView.getMeasuredHeight() * childCount;
            setMeasuredDimension(widthSpaceSize, measuredHeight);
        } else if (widthSpecMode == MeasureSpec.AT_MOST) {
            final View childView = getChildAt(0);//因為這裡的child都是同類,所以偷懶~取第一個測量尺寸就夠啦
            measuredWidth = childView.getMeasuredWidth() * childCount;
            setMeasuredDimension(measuredWidth, heightSpaceSize);
        } else {
            setMeasuredDimension(widthSpaceSize, heightSpaceSize);

        }

    }

    @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) {
            scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
            postInvalidate();
        }
    }

    @Override
    protected void onDetachedFromWindow() {
        mVelocityTracker.recycle();
        super.onDetachedFromWindow();
    }

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

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

    }

    public HorizontalScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();

    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    public HorizontalScrollView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init();

    }

}

總結

對於第一種,思路是在ACTION_MOVE的時候,判斷x偏移量是否大於y的偏移量.如果大於,就page++,.

對於第二種,需要判斷子view是否滑動到了頂部,或者底部,如果是,讓父控制元件滑動即可.

對於第三種,需要結合第一種,和第二種進行判斷.

在判斷滑動衝突的過程中,重點放在 InterceptTouchEvent()中,還有TouchEvent種進行處理.