Question

我想在HorizontalScrollView中实现Snapping effect，即当用户水平滚动时，最明显的项目（项目可见＆gt; 50％）到达中心。

我尝试使用

执行此操作

 hsv.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
            @Override
            public void onScrollChanged() {
                int scrollX = hsv.getScrollX(); // For HorizontalScrollView
                Log.e("scrollX",String.valueOf(scrollX));
                // DO SOMETHING WITH THE SCROLL COORDINATES
            }
        });

但即使我们不触摸屏幕，该值也不会保持不变。

以下是logcat的一部分：

    03-28 11:11:22.116 26639-26639/package_name E/scrollX: 0
03-28 11:11:22.133 26639-26639/package_name E/scrollX: 792
03-28 11:11:22.133 26639-26639/package_name E/scrollX: 0
03-28 11:11:22.151 26639-26639/package_name E/scrollX: 795
03-28 11:11:22.151 26639-26639/package_name E/scrollX: 0
03-28 11:11:22.166 26639-26639/package_name E/scrollX: 799
03-28 11:11:22.166 26639-26639/package_name E/scrollX: 0
03-28 11:11:22.183 26639-26639/package_name E/scrollX: 801
03-28 11:11:22.183 26639-26639/package_name E/scrollX: 0
03-28 11:11:22.199 26639-26639/package_name E/scrollX: 803
03-28 11:11:22.199 26639-26639/package_name E/scrollX: 0
03-28 11:11:22.216 26639-26639/package_name E/scrollX: 804
03-28 11:11:22.216 26639-26639/package_name E/scrollX: 0
03-28 11:11:22.233 26639-26639/package_name E/scrollX: 805
03-28 11:11:22.233 26639-26639/package_name E/scrollX: 0
03-28 11:11:22.249 26639-26639/package_name E/scrollX: 806
03-28 11:11:22.249 26639-26639/package_name E/scrollX: 0

现在我已经尝试过这些解决方案，I am not getting the point或I don't know to do it。请帮忙。

HorizontalScrollView within ScrollView Touch Handling
HorizontalScrollView with snapping effect
Creating Custom Horizontal Scroll View With Snap or paging
Creating a “Snapping” Horizontal Scroll View

我的用例：我有一个HorizontalScrollView附加到Recyclerview（垂直）的适配器，所以snapHelper可以垂直完成，但我不知道如何使它成为水平。

Answer 1

Here是自定义水平滚动视图的完整代码，用于捕捉项目。

    public class HomeFeatureLayout extends HorizontalScrollView {
    private static final int SWIPE_MIN_DISTANCE = 5;
    private static final int SWIPE_THRESHOLD_VELOCITY = 300;

    private ArrayList mItems = null;
    private GestureDetector mGestureDetector;
    private int mActiveFeature = 0;

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

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

    public HomeFeatureLayout(Context context) {
        super(context);
    }

    public void setFeatureItems(ArrayList items){
        LinearLayout internalWrapper = new LinearLayout(getContext());
        internalWrapper.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));
        internalWrapper.setOrientation(LinearLayout.HORIZONTAL);
        addView(internalWrapper);
        this.mItems = items;
        for(int i = 0; i< items.size();i++){
            LinearLayout featureLayout = (LinearLayout) View.inflate(this.getContext(),R.layout.homefeature,null);
            //...
          //Create the view for each screen in the scroll view
            //...
            internalWrapper.addView(featureLayout);
        }
        setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                //If the user swipes
                if (mGestureDetector.onTouchEvent(event)) {
                    return true;
                }
                else if(event.getAction() == MotionEvent.ACTION_UP || event.getAction() == MotionEvent.ACTION_CANCEL ){
                    int scrollX = getScrollX();
                    int featureWidth = v.getMeasuredWidth();
                    mActiveFeature = ((scrollX + (featureWidth/2))/featureWidth);
                    int scrollTo = mActiveFeature*featureWidth;
                    smoothScrollTo(scrollTo, 0);
                    return true;
                }
                else{
                    return false;
                }
            }
        });
        mGestureDetector = new GestureDetector(new MyGestureDetector());
    }
        class MyGestureDetector extends SimpleOnGestureListener {
        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            try {
                //right to left
                if(e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
                    int featureWidth = getMeasuredWidth();
                    mActiveFeature = (mActiveFeature < (mItems.size() - 1))? mActiveFeature + 1:mItems.size() -1;
                    smoothScrollTo(mActiveFeature*featureWidth, 0);
                    return true;
                }
                //left to right
                else if (e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
                    int featureWidth = getMeasuredWidth();
                    mActiveFeature = (mActiveFeature > 0)? mActiveFeature - 1:0;
                    smoothScrollTo(mActiveFeature*featureWidth, 0);
                    return true;
                }
            } catch (Exception e) {
                    Log.e("Fling", "There was an error processing the Fling event:" + e.getMessage());
            }
            return false;
        }
    }
}

此示例以编程方式添加视图并将其称为Features。但您可以简单地更改该行为并使用getChildrenCount()代替mItems.size()等等。

重要的部分是GestureDetector和TouchListener。在TouchListener中，您可以收听用户手指被移除时的ACTION_UP（如滚动后），并根据滚动量及其值计算哪个视图为active位置。你也可以添加一个GestureDetector来捕捉fling操作并在那里做同样的事情。

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