core/java/android/widget/DropDownListView.java

/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.widget;


import com.android.internal.widget.AutoScrollHelper.AbsListViewAutoScroller;

import android.annotation.NonNull;
import android.content.Context;
import android.view.MotionEvent;
import android.view.View;

/**
 * Wrapper class for a ListView. This wrapper can hijack the focus to
 * make sure the list uses the appropriate drawables and states when
 * displayed on screen within a drop down. The focus is never actually
 * passed to the drop down in this mode; the list only looks focused.
 *
 * @hide
 */
public class DropDownListView extends ListView {
    /*
     * WARNING: This is a workaround for a touch mode issue.
     *
     * Touch mode is propagated lazily to windows. This causes problems in
     * the following scenario:
     * - Type something in the AutoCompleteTextView and get some results
     * - Move down with the d-pad to select an item in the list
     * - Move up with the d-pad until the selection disappears
     * - Type more text in the AutoCompleteTextView *using the soft keyboard*
     *   and get new results; you are now in touch mode
     * - The selection comes back on the first item in the list, even though
     *   the list is supposed to be in touch mode
     *
     * Using the soft keyboard triggers the touch mode change but that change
     * is propagated to our window only after the first list layout, therefore
     * after the list attempts to resurrect the selection.
     *
     * The trick to work around this issue is to pretend the list is in touch
     * mode when we know that the selection should not appear, that is when
     * we know the user moved the selection away from the list.
     *
     * This boolean is set to true whenever we explicitly hide the list's
     * selection and reset to false whenever we know the user moved the
     * selection back to the list.
     *
     * When this boolean is true, isInTouchMode() returns true, otherwise it
     * returns super.isInTouchMode().
     */
    private boolean mListSelectionHidden;

    /**
     * True if this wrapper should fake focus.
     */
    private boolean mHijackFocus;

    /** Whether to force drawing of the pressed state selector. */
    private boolean mDrawsInPressedState;

    /** Helper for drag-to-open auto scrolling. */
    private AbsListViewAutoScroller mScrollHelper;

    /**
     * Creates a new list view wrapper.
     *
     * @param context this view's context
     */
    public DropDownListView(@NonNull Context context, boolean hijackFocus) {
        this(context, hijackFocus, com.android.internal.R.attr.dropDownListViewStyle);
    }

    /**
     * Creates a new list view wrapper.
     *
     * @param context this view's context
     */
    public DropDownListView(@NonNull Context context, boolean hijackFocus, int defStyleAttr) {
        super(context, null, defStyleAttr);
        mHijackFocus = hijackFocus;
        // TODO: Add an API to control this
        setCacheColorHint(0); // Transparent, since the background drawable could be anything.
    }

    @Override
    boolean shouldShowSelector() {
        return isHovered() || super.shouldShowSelector();
    }

    @Override
    public boolean onHoverEvent(@NonNull MotionEvent ev) {
        // Allow the super class to handle hover state management first.
        final boolean handled = super.onHoverEvent(ev);

        final int action = ev.getActionMasked();
        if (action == MotionEvent.ACTION_HOVER_ENTER
                || action == MotionEvent.ACTION_HOVER_MOVE) {
            final int position = pointToPosition((int) ev.getX(), (int) ev.getY());
            if (position != INVALID_POSITION && position != mSelectedPosition) {
                final View hoveredItem = getChildAt(position - getFirstVisiblePosition());
                if (hoveredItem.isEnabled()) {
                    // Force a focus so that the proper selector state gets used when we update.
                    requestFocus();

                    positionSelector(position, hoveredItem);
                    setSelectedPositionInt(position);
                    setNextSelectedPositionInt(position);
                }
                updateSelectorState();
            }
        } else {
            // Do not cancel the selected position if the selection is visible by other reasons.
            if (!super.shouldShowSelector()) {
                setSelectedPositionInt(INVALID_POSITION);
                setNextSelectedPositionInt(INVALID_POSITION);
            }
        }

        return handled;
    }

    /**
     * Handles forwarded events.
     *
     * @param activePointerId id of the pointer that activated forwarding
     * @return whether the event was handled
     */
    public boolean onForwardedEvent(@NonNull MotionEvent event, int activePointerId) {
        boolean handledEvent = true;
        boolean clearPressedItem = false;

        final int actionMasked = event.getActionMasked();
        switch (actionMasked) {
            case MotionEvent.ACTION_CANCEL:
                handledEvent = false;
                break;
            case MotionEvent.ACTION_UP:
                handledEvent = false;
                // $FALL-THROUGH$
            case MotionEvent.ACTION_MOVE:
                final int activeIndex = event.findPointerIndex(activePointerId);
                if (activeIndex < 0) {
                    handledEvent = false;
                    break;
                }

                final int x = (int) event.getX(activeIndex);
                final int y = (int) event.getY(activeIndex);
                final int position = pointToPosition(x, y);
                if (position == INVALID_POSITION) {
                    clearPressedItem = true;
                    break;
                }

                final View child = getChildAt(position - getFirstVisiblePosition());
                setPressedItem(child, position, x, y);
                handledEvent = true;

                if (actionMasked == MotionEvent.ACTION_UP) {
                    final long id = getItemIdAtPosition(position);
                    performItemClick(child, position, id);
                }
                break;
        }

        // Failure to handle the event cancels forwarding.
        if (!handledEvent || clearPressedItem) {
            clearPressedItem();
        }

        // Manage automatic scrolling.
        if (handledEvent) {
            if (mScrollHelper == null) {
                mScrollHelper = new AbsListViewAutoScroller(this);
            }
            mScrollHelper.setEnabled(true);
            mScrollHelper.onTouch(this, event);
        } else if (mScrollHelper != null) {
            mScrollHelper.setEnabled(false);
        }

        return handledEvent;
    }

    /**
     * Sets whether the list selection is hidden, as part of a workaround for a touch mode issue
     * (see the declaration for mListSelectionHidden).
     * @param listSelectionHidden
     */
    public void setListSelectionHidden(boolean listSelectionHidden) {
        this.mListSelectionHidden = listSelectionHidden;
    }

    private void clearPressedItem() {
        mDrawsInPressedState = false;
        setPressed(false);
        updateSelectorState();

        final View motionView = getChildAt(mMotionPosition - mFirstPosition);
        if (motionView != null) {
            motionView.setPressed(false);
        }
    }

    private void setPressedItem(@NonNull View child, int position, float x, float y) {
        mDrawsInPressedState = true;

        // Ordering is essential. First, update the container's pressed state.
        drawableHotspotChanged(x, y);
        if (!isPressed()) {
            setPressed(true);
        }

        // Next, run layout if we need to stabilize child positions.
        if (mDataChanged) {
            layoutChildren();
        }

        // Manage the pressed view based on motion position. This allows us to
        // play nicely with actual touch and scroll events.
        final View motionView = getChildAt(mMotionPosition - mFirstPosition);
        if (motionView != null && motionView != child && motionView.isPressed()) {
            motionView.setPressed(false);
        }
        mMotionPosition = position;

        // Offset for child coordinates.
        final float childX = x - child.getLeft();
        final float childY = y - child.getTop();
        child.drawableHotspotChanged(childX, childY);
        if (!child.isPressed()) {
            child.setPressed(true);
        }

        // Ensure that keyboard focus starts from the last touched position.
        setSelectedPositionInt(position);
        positionSelectorLikeTouch(position, child, x, y);

        // Refresh the drawable state to reflect the new pressed state,
        // which will also update the selector state.
        refreshDrawableState();
    }

    @Override
    boolean touchModeDrawsInPressedState() {
        return mDrawsInPressedState || super.touchModeDrawsInPressedState();
    }

    /**
     * Avoids jarring scrolling effect by ensuring that list elements
     * made of a text view fit on a single line.
     *
     * @param position the item index in the list to get a view for
     * @return the view for the specified item
     */
    @Override
    View obtainView(int position, boolean[] isScrap) {
        View view = super.obtainView(position, isScrap);

        if (view instanceof TextView) {
            ((TextView) view).setHorizontallyScrolling(true);
        }

        return view;
    }

    @Override
    public boolean isInTouchMode() {
        // WARNING: Please read the comment where mListSelectionHidden is declared
        return (mHijackFocus && mListSelectionHidden) || super.isInTouchMode();
    }

    /**
     * Returns the focus state in the drop down.
     *
     * @return true always if hijacking focus
     */
    @Override
    public boolean hasWindowFocus() {
        return mHijackFocus || super.hasWindowFocus();
    }

    /**
     * Returns the focus state in the drop down.
     *
     * @return true always if hijacking focus
     */
    @Override
    public boolean isFocused() {
        return mHijackFocus || super.isFocused();
    }

    /**
     * Returns the focus state in the drop down.
     *
     * @return true always if hijacking focus
     */
    @Override
    public boolean hasFocus() {
        return mHijackFocus || super.hasFocus();
    }
}