View parent's onTouch method is only called when the child that's being touched is not clickable

Question

I needed to intercept the touch events for a DialogFragment , so I overrode it's view's parent's onInterceptTouchEvent like so:

@Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        ViewGroup viewGroup = new FrameLayout(GlobalState.getContext()){
            @Override
            public boolean onInterceptTouchEvent(MotionEvent ev) {
                mDecorView.onTouchEvent(ev);
                return super.onInterceptTouchEvent(ev);
            }
        };
        View view = inflater.inflate(R.layout.enter_number_dialog_layout,container);
        viewGroup.addView(view);
        return viewGroup;
    }

As you can see, I call mDecorView.onTouchEvent whenever the fragment is touched. However, the problem is, even though I know interceptOnTouchEvent is always called when the fragment's layout is touched -- placed a breakpoint on the mDecorView.onTouchEvent line -- mDecorView 's OnTouchListener.onTouch is only executed when the TextView is touched, but not when anything inside the GridLayout is; which are the only two direct children. I know this because I placed a breakpoint on the first line of code in my implementation of onTouch , and it's always called when the TextView is touched, but not when the GridLayout is.

Here is my fragment's layout:

    <TextView
        android:id="@+id/number_text_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:hint="$"
        android:singleLine="true"
        android:textSize="40sp"/>

    <GridLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:columnCount="3"
        android:orientation="horizontal">

        <Button
            android:id="@+id/the_1_button"
            android:background="@android:color/white"
            android:text="1"/>

        <Button
            android:id="@+id/the_2_button"
            android:background="@android:color/white"
            android:text="2"/>

        <Button
            android:id="@+id/the_3_button"
            android:background="@android:color/white"
            android:text="3"/>

        <Button
            android:id="@+id/the_4_button"
            android:background="@android:color/white"
            android:text="4"/>

        <Button
            android:id="@+id/the_5_button"
            android:background="@android:color/white"
            android:text="5"/>

        <Button
            android:id="@+id/the_6_button"
            android:background="@android:color/white"
            android:text="6"/>

        <Button
            android:id="@+id/the_7_button"
            android:background="@android:color/white"
            android:text="7"/>

        <Button
            android:id="@+id/the_8_button"
            android:background="@android:color/white"
            android:text="8"/>

        <Button
            android:id="@+id/the_9_button"
            android:background="@android:color/white"
            android:text="9"/>

        <ImageButton
            android:id="@+id/the_backspace_button"
            style="@style/Widget.AppCompat.Button"
            android:background="@android:color/white"
            android:src="@drawable/ic_backspace"/>

        <Button
            android:id="@+id/the_0_button"
            android:background="@android:color/white"
            android:text="0"/>

        <Button
            android:id="@+id/the_done_button"
            android:background="@android:color/white"
            android:text="done"/>
    </GridLayout>

</LinearLayout>

Any idea why mDecorView 's OnTouchListener.onTouch is not being called when the GridLayout is touched?

Update:

Here is the body of mDecorView 's OnTouchListener 's onTouch() :

@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
    // offset because the view is translated during swipe
    motionEvent.offsetLocation(mTranslationX, 0);

    if (mViewWidth < 2) {
        mViewWidth = mView.getWidth();
    }

    switch (motionEvent.getActionMasked()) {
        case MotionEvent.ACTION_DOWN: {
            // TODO: ensure this is a finger, and set a flag
            mDownX = motionEvent.getRawX();
            mDownY = motionEvent.getRawY();
            if (mCallbacks.canDismiss(mToken)) {
                mVelocityTracker = VelocityTracker.obtain();
                mVelocityTracker.addMovement(motionEvent);
            }
            break;
        }

        case MotionEvent.ACTION_UP: {
            if (mVelocityTracker == null) {
                break;
            }

            float deltaX = motionEvent.getRawX() - mDownX;
            mVelocityTracker.addMovement(motionEvent);
            mVelocityTracker.computeCurrentVelocity(1000);
            float velocityX = mVelocityTracker.getXVelocity();
            float absVelocityX = Math.abs(velocityX);
            float absVelocityY = Math.abs(mVelocityTracker.getYVelocity());
            boolean dismiss = false;
            boolean dismissRight = false;
            if (Math.abs(deltaX) > mViewWidth / 2 && mSwiping) {
                dismiss = true;
                dismissRight = deltaX > 0;
            } else if (mMinFlingVelocity <= absVelocityX && absVelocityX <= mMaxFlingVelocity
                    && absVelocityY < absVelocityX
                    && absVelocityY < absVelocityX && mSwiping) {
                // dismiss only if flinging in the same direction as dragging
                dismiss = (velocityX < 0) == (deltaX < 0);
                dismissRight = mVelocityTracker.getXVelocity() > 0;
            }
            if (dismiss) {
                // dismiss
                mView.animate()
                        .translationX(dismissRight ? mViewWidth : -mViewWidth)
                        .alpha(0)
                        .setDuration(mAnimationTime)
                        .setListener(new AnimatorListenerAdapter() {
                            @Override
                            public void onAnimationEnd(Animator animation) {
                                performDismiss();
                            }
                        });
                return true;
            } else if (mSwiping) {
                // cancel
                mView.animate()
                        .translationX(0)
                        .alpha(1)
                        .setDuration(mAnimationTime)
                        .setListener(null);
            }
            mVelocityTracker.recycle();
            mVelocityTracker = null;
            mTranslationX = 0;
            mDownX = 0;
            mDownY = 0;
            mSwiping = false;
            break;
        }

        case MotionEvent.ACTION_CANCEL: {
            if (mVelocityTracker == null) {
                break;
            }

            mView.animate()
                    .translationX(0)
                    .alpha(1)
                    .setDuration(mAnimationTime)
                    .setListener(null);
            mVelocityTracker.recycle();
            mVelocityTracker = null;
            mTranslationX = 0;
            mDownX = 0;
            mDownY = 0;
            mSwiping = false;
            break;
        }

        case MotionEvent.ACTION_MOVE: {
            if (mVelocityTracker == null) {
                break;
            }

            mVelocityTracker.addMovement(motionEvent);
            float deltaX = motionEvent.getRawX() - mDownX;
            float deltaY = motionEvent.getRawY() - mDownY;
            if (Math.abs(deltaX) > mSlop && Math.abs(deltaY) < Math.abs(deltaX) / 2) {
                mSwiping = true;
                mSwipingSlop = (deltaX > 0 ? mSlop : -mSlop);
                mView.getParent().requestDisallowInterceptTouchEvent(true);

                // Cancel listview's touch
                MotionEvent cancelEvent = MotionEvent.obtain(motionEvent);
                cancelEvent.setAction(MotionEvent.ACTION_CANCEL |
                        (motionEvent.getActionIndex() <<
                                MotionEvent.ACTION_POINTER_INDEX_SHIFT));
                mView.onTouchEvent(cancelEvent);
                cancelEvent.recycle();
            }

            if (mSwiping) {
                mTranslationX = deltaX;
                mView.setTranslationX(deltaX - mSwipingSlop);
                // TODO: use an ease-out interpolator or such
                mView.setAlpha(Math.max(0f, Math.min(1f,
                        1f - 2f * Math.abs(deltaX) / mViewWidth)));
                return true;
            }
            break;
        }
    }
    return false;
}

Answer 1

Callback methods are designed to be called by the event handling system, not by your own code. When events share functionality, it is best to put the common code in a method which can be called by any callback method. This is preferable to calling a callback directly yourself because you have more control. You know exactly when the method will execute and you can accept only parameters which are meaningful to the task at hand.