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/*
* Copyright (C) 2011 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.dialer;
import android.view.View;
import android.widget.AbsListView;
import android.widget.ListView;
/**
* Handles scrolling back of a list tied to a header.
* <p>
* This is used to implement a header that scrolls up with the content of a list to be partially
* obscured.
*/
public class BackScrollManager {
/** Defines the header to be scrolled. */
public interface ScrollableHeader {
/** Sets the offset by which to scroll. */
public void setOffset(int offset);
/** Gets the maximum offset that should be applied to the header. */
public int getMaximumScrollableHeaderOffset();
}
private final ScrollableHeader mHeader;
private final ListView mListView;
private final AbsListView.OnScrollListener mScrollListener =
new AbsListView.OnScrollListener() {
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount,
int totalItemCount) {
if (firstVisibleItem != 0) {
// The first item is not shown, the header should be pinned at the top.
mHeader.setOffset(mHeader.getMaximumScrollableHeaderOffset());
return;
}
View firstVisibleItemView = view.getChildAt(firstVisibleItem);
if (firstVisibleItemView == null) {
return;
}
// We scroll the header up, but at most pin it to the top of the screen.
int offset = Math.min(
(int) -view.getChildAt(firstVisibleItem).getY(),
mHeader.getMaximumScrollableHeaderOffset());
mHeader.setOffset(offset);
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// Nothing to do here.
}
};
/**
* Creates a new instance of a {@link BackScrollManager} that connected the header and the list
* view.
*/
public static void bind(ScrollableHeader header, ListView listView) {
BackScrollManager backScrollManager = new BackScrollManager(header, listView);
backScrollManager.bind();
}
private BackScrollManager(ScrollableHeader header, ListView listView) {
mHeader = header;
mListView = listView;
}
private void bind() {
mListView.setOnScrollListener(mScrollListener);
// We disable the scroll bar because it would otherwise be incorrect because of the hidden
// header.
mListView.setVerticalScrollBarEnabled(false);
}
}
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