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Diffstat (limited to 'src/com/android/launcher3/list/AutoScrollListView.java')
-rw-r--r-- | src/com/android/launcher3/list/AutoScrollListView.java | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/src/com/android/launcher3/list/AutoScrollListView.java b/src/com/android/launcher3/list/AutoScrollListView.java new file mode 100644 index 000000000..733a753c1 --- /dev/null +++ b/src/com/android/launcher3/list/AutoScrollListView.java @@ -0,0 +1,117 @@ +/* + * Copyright (C) 2010 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 com.android.launcher3.list; + +import android.content.Context; +import android.util.AttributeSet; +import android.widget.ListView; + +/** + * A ListView that can be asked to scroll (smoothly or otherwise) to a specific + * position. This class takes advantage of similar functionality that exists + * in {@link ListView} and enhances it. + */ +public class AutoScrollListView extends ListView { + + /** + * Position the element at about 1/3 of the list height + */ + private static final float PREFERRED_SELECTION_OFFSET_FROM_TOP = 0.33f; + + private int mRequestedScrollPosition = -1; + private boolean mSmoothScrollRequested; + + public AutoScrollListView(Context context) { + super(context); + } + + public AutoScrollListView(Context context, AttributeSet attrs) { + super(context, attrs); + } + + public AutoScrollListView(Context context, AttributeSet attrs, int defStyle) { + super(context, attrs, defStyle); + } + + /** + * Brings the specified position to view by optionally performing a jump-scroll maneuver: + * first it jumps to some position near the one requested and then does a smooth + * scroll to the requested position. This creates an impression of full smooth + * scrolling without actually traversing the entire list. If smooth scrolling is + * not requested, instantly positions the requested item at a preferred offset. + */ + public void requestPositionToScreen(int position, boolean smoothScroll) { + mRequestedScrollPosition = position; + mSmoothScrollRequested = smoothScroll; + requestLayout(); + } + + @Override + protected void layoutChildren() { + super.layoutChildren(); + if (mRequestedScrollPosition == -1) { + return; + } + + final int position = mRequestedScrollPosition; + mRequestedScrollPosition = -1; + + int firstPosition = getFirstVisiblePosition() + 1; + int lastPosition = getLastVisiblePosition(); + if (position >= firstPosition && position <= lastPosition) { + return; // Already on screen + } + + final int offset = (int) (getHeight() * PREFERRED_SELECTION_OFFSET_FROM_TOP); + if (!mSmoothScrollRequested) { + setSelectionFromTop(position, offset); + + // Since we have changed the scrolling position, we need to redo child layout + // Calling "requestLayout" in the middle of a layout pass has no effect, + // so we call layoutChildren explicitly + super.layoutChildren(); + + } else { + // We will first position the list a couple of screens before or after + // the new selection and then scroll smoothly to it. + int twoScreens = (lastPosition - firstPosition) * 2; + int preliminaryPosition; + if (position < firstPosition) { + preliminaryPosition = position + twoScreens; + if (preliminaryPosition >= getCount()) { + preliminaryPosition = getCount() - 1; + } + if (preliminaryPosition < firstPosition) { + setSelection(preliminaryPosition); + super.layoutChildren(); + } + } else { + preliminaryPosition = position - twoScreens; + if (preliminaryPosition < 0) { + preliminaryPosition = 0; + } + if (preliminaryPosition > lastPosition) { + setSelection(preliminaryPosition); + super.layoutChildren(); + } + } + + + smoothScrollToPositionFromTop(position, offset); + } + } +}
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