如何区分CustomView与ScrollView的触摸事件并解决事件冲突？

Hey there! Dealing with touch event conflicts between a ScrollView and its child CustomView is super common in Android development, but we can fix this cleanly using the platform's built-in touch dispatch system. Let's break down the two scenarios you mentioned and how to handle each:

1. Prevent ScrollView from triggering events when interacting with your CustomView #

The key here is to tell the ScrollView to stop intercepting touch events once the user starts interacting with your CustomView. We can do this using requestDisallowInterceptTouchEvent() in the CustomView's touch handling:

public class YourCustomView extends View {
    // Add your constructors here...

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getActionMasked()) {
            case MotionEvent.ACTION_DOWN:
                // Notify the parent ScrollView not to intercept any touch events from this point on
                getParent().requestDisallowInterceptTouchEvent(true);
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                // Re-enable the ScrollView's intercept capability once the interaction ends
                getParent().requestDisallowInterceptTouchEvent(false);
                break;
        }

        // Add your CustomView's touch logic here (e.g., clicks, custom gestures)
        // ...

        return true; // Return true to indicate we've handled the event
    }
}

When the user first touches the CustomView (ACTION_DOWN), we lock the ScrollView out of the touch event chain. Once the interaction finishes (lift finger or event gets canceled), we unlock it so the ScrollView can handle scrolling again.

2. Prevent CustomView from receiving touch events when scrolling the ScrollView #

To stop the CustomView from getting touch events during a scroll, we need the ScrollView to intercept the event early if it detects a scrolling gesture. The best way is to create a custom ScrollView subclass and override onInterceptTouchEvent():

public class CustomScrollView extends ScrollView {
    private YourCustomView mCustomView;
    private float mInitialTouchY;
    private final int SCROLL_THRESHOLD = dpToPx(10); // Adjust this threshold as needed

    // Add your constructors here...

    // Call this to set a reference to your CustomView
    public void targetCustomView(YourCustomView customView) {
        mCustomView = customView;
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        if (mCustomView != null) {
            Rect viewBounds = new Rect();
            mCustomView.getHitRect(viewBounds);

            // Check if the touch is happening within the CustomView's bounds
            if (viewBounds.contains((int) event.getX(), (int) event.getY())) {
                switch (event.getActionMasked()) {
                    case MotionEvent.ACTION_DOWN:
                        mInitialTouchY = event.getY();
                        return false; // Let the CustomView handle the initial touch
                    case MotionEvent.ACTION_MOVE:
                        float touchDeltaY = Math.abs(event.getY() - mInitialTouchY);
                        // If the user is scrolling past our threshold, intercept the event
                        if (touchDeltaY > SCROLL_THRESHOLD) {
                            return true; // Take over the event to scroll the ScrollView
                        }
                        break;
                }
                // Default: let the CustomView keep handling the event
                return false;
            }
        }
        // For touches outside the CustomView, use the default ScrollView behavior
        return super.onInterceptTouchEvent(event);
    }

    private int dpToPx(int dp) {
        return (int) TypedValue.applyDimension(
                TypedValue.COMPLEX_UNIT_DIP,
                dp,
                getResources().getDisplayMetrics()
        );
    }
}

How this works: #

• When the user touches inside the CustomView, we first let the CustomView get the ACTION_DOWN event.
• If the user starts scrolling (movement exceeds our threshold), the ScrollView intercepts the event and takes over, so the CustomView won't receive any subsequent touch events.
• For touches outside the CustomView, the ScrollView behaves normally.

Don't forget to link your custom ScrollView and CustomView in code:

CustomScrollView scrollView = findViewById(R.id.your_scroll_view);
YourCustomView customView = findViewById(R.id.your_custom_view);
scrollView.targetCustomView(customView);

Quick Notes #

• Adjust the SCROLL_THRESHOLD value to match your app's needs (smaller values mean the ScrollView takes over faster).
• If your CustomView has child views, make sure their touch handling doesn't interfere with this logic (you might need to propagate the requestDisallowInterceptTouchEvent call if needed).
• For horizontal ScrollViews, adjust the logic to use X-axis values instead of Y.

内容的提问来源于stack exchange，提问作者suresh