Android源码分析：HeaderViewListAdapter
http://bj007.blog.51cto.com/1701577/643568
对于手机开发，我一直坚持的是“用iPhone的方式开发iPhone应用，用Android的方式开发Android应用”。但如何去把握iPhone 或者Android的方式呢？在iPhone开发时可能需要看大量Apple文档。而Android在看文档的同时还可以看看源码。这源码中有时可以发现 一些内部实现加深理解，有时可以受到某些可以在应用中使用的启发。总之源码是一个需要去发掘的“矿场”，时而不时地都会发现一些“金子”。
在Android开发的时候经常会有一些列表数据分组显示的需求，对于iPhone来说修改下模型数据并设置下风格就可以轻松搞定（如下图）。但对于 Android这种需求就会有些痛苦了。因为系统提供的ListAdapter无法提供这种支持，因此只能自定义Adapter。为了实现该功 能，Adapter通常就开始充斥很多特殊处理以及各种硬编码。如何用Android的方式设计和实现一个自定义Adapter呢？源码中的 HeaderViewListAdapter可能会提供些答案或者启发。
图1：Group分隔的iPhone表格
注释版本的HeaderViewListAdapter.java如下：
/*如果List需要有标题就会使用该ListAdapter。该ListAdapter包装了另一个ListAdapter并保存着
标题视图和相关数据对象。该类是作为基类，在代码中可能不需要直接使用。
*/
// 类名有点不确切，其实是支持Header和Footter的
public class HeaderViewListAdapter implements WrapperListAdapter, Filterable {
private final ListAdapter mAdapter;
// These two ArrayList are assumed to NOT be null.
// They are indeed created when declared in ListView and then shared.
ArrayList<ListView.FixedViewInfo> mHeaderViewInfos;
ArrayList<ListView.FixedViewInfo> mFooterViewInfos;
// Used as a placeholder in case the provided info views are indeed null.
// Currently only used by some CTS tests, which may be removed.
static final ArrayList<ListView.FixedViewInfo> EMPTY_INFO_LIST =
new ArrayList<ListView.FixedViewInfo>();
boolean mAreAllFixedViewsSelectable;
/// 这是个很有趣的概念，之后我们会一起了解
private final boolean mIsFilterable;
public HeaderViewListAdapter(ArrayList<ListView.FixedViewInfo> headerViewInfos,
ArrayList<ListView.FixedViewInfo> footerViewInfos,
ListAdapter adapter) {
mAdapter = adapter;
mIsFilterable = adapter instanceof Filterable;
/// 很好的处理，这里实际是使用了一种Null对象模式
if (headerViewInfos == null) {
mHeaderViewInfos = EMPTY_INFO_LIST;
} else {
mHeaderViewInfos = headerViewInfos;
}
if (footerViewInfos == null) {
mFooterViewInfos = EMPTY_INFO_LIST;
} else {
mFooterViewInfos = footerViewInfos;
}
mAreAllFixedViewsSelectable =
areAllListInfosSelectable(mHeaderViewInfos)
&& areAllListInfosSelectable(mFooterViewInfos);
}
/// 支持多个标题栏哦
public int getHeadersCount() {
return mHeaderViewInfos.size();
}
/// 支持多个尾注栏哦
public int getFootersCount() {
return mFooterViewInfos.size();
}
public boolean isEmpty() {
return mAdapter == null || mAdapter.isEmpty();
}
/// FixedViewInfo名字很贴切，这是相对于包装Adapter中的可变数据命名的
private boolean areAllListInfosSelectable(ArrayList<ListView.FixedViewInfo> infos) {
if (infos != null) {
for (ListView.FixedViewInfo info : infos) {
if (!info.isSelectable) {
return false;
}
}
}
return true;
}
/// 支持标题删减
public boolean removeHeader(View v) {
for (int i = 0; i < mHeaderViewInfos.size(); i++) {
ListView.FixedViewInfo info = mHeaderViewInfos.get(i);
if (info.view == v) {
mHeaderViewInfos.remove(i);
mAreAllFixedViewsSelectable =
areAllListInfosSelectable(mHeaderViewInfos)
&& areAllListInfosSelectable(mFooterViewInfos);
return true;
}
}
return false;
}
/// 支持尾注删减
public boolean removeFooter(View v) {
for (int i = 0; i < mFooterViewInfos.size(); i++) {
ListView.FixedViewInfo info = mFooterViewInfos.get(i);
if (info.view == v) {
mFooterViewInfos.remove(i);
mAreAllFixedViewsSelectable =
areAllListInfosSelectable(mHeaderViewInfos)
&& areAllListInfosSelectable(mFooterViewInfos);
return true;
}
}
return false;
}
/// 标题视图、尾注视图和普通的数据视图，一视同仁
public int getCount() {
if (mAdapter != null) {
return getFootersCount() + getHeadersCount() + mAdapter.getCount();
} else {
return getFootersCount() + getHeadersCount();
}
}
public boolean areAllItemsEnabled() {
if (mAdapter != null) {
return mAreAllFixedViewsSelectable && mAdapter.areAllItemsEnabled();
} else {
return true;
}
}
public boolean isEnabled(int position) {
// Header (negative positions will throw an ArrayIndexOutOfBoundsException)
int numHeaders = getHeadersCount();
if (position < numHeaders) {
return mHeaderViewInfos.get(position).isSelectable;
}
// Adapter
final int adjPosition = position - numHeaders;
int adapterCount = 0;
if (mAdapter != null) {
adapterCount = mAdapter.getCount();
if (adjPosition < adapterCount) {
return mAdapter.isEnabled(adjPosition);
}
}
// Footer (off-limits positions will throw an ArrayIndexOutOfBoundsException)
return mFooterViewInfos.get(adjPosition - adapterCount).isSelectable;
}
/// 需要分段处理
public Object getItem(int position) {
// Header (negative positions will throw an ArrayIndexOutOfBoundsException)
int numHeaders = getHeadersCount();
if (position < numHeaders) {
return mHeaderViewInfos.get(position).data;
}
// Adapter
final int adjPosition = position - numHeaders;
int adapterCount = 0;
if (mAdapter != null) {
adapterCount = mAdapter.getCount();
if (adjPosition < adapterCount) {
return mAdapter.getItem(adjPosition);
}
}
// Footer (off-limits positions will throw an ArrayIndexOutOfBoundsException)
return mFooterViewInfos.get(adjPosition - adapterCount).data;
}
/// 这可不包括Header和Footer
public long getItemId(int position) {
int numHeaders = getHeadersCount();
if (mAdapter != null && position >= numHeaders) {
int adjPosition = position - numHeaders;
int adapterCount = mAdapter.getCount();
if (adjPosition < adapterCount) {
return mAdapter.getItemId(adjPosition);
}
}
return -1;
}
public boolean hasStableIds() {
if (mAdapter != null) {
return mAdapter.hasStableIds();
}
return false;
}
/// 需要分段处理，其中Header和Footer视图已经事先存储在ListView.FixedViewInfo对象中了
public View getView(int position, View convertView, ViewGroup parent) {
// Header (negative positions will throw an ArrayIndexOutOfBoundsException)
int numHeaders = getHeadersCount();
if (position < numHeaders) {
return mHeaderViewInfos.get(position).view;
}
// Adapter
final int adjPosition = position - numHeaders;
int adapterCount = 0;
if (mAdapter != null) {
adapterCount = mAdapter.getCount();
if (adjPosition < adapterCount) {
return mAdapter.getView(adjPosition, convertView, parent);
}
}
// Footer (off-limits positions will throw an ArrayIndexOutOfBoundsException)
return mFooterViewInfos.get(adjPosition - adapterCount).view;
}
/// 支持同一个List中不同类型的视图
public int getItemViewType(int position) {
int numHeaders = getHeadersCount();
if (mAdapter != null && position >= numHeaders) {
int adjPosition = position - numHeaders;
int adapterCount = mAdapter.getCount();
if (adjPosition < adapterCount) {
return mAdapter.getItemViewType(adjPosition);
}
}
return AdapterView.ITEM_VIEW_TYPE_HEADER_OR_FOOTER;
}
public int getViewTypeCount() {
if (mAdapter != null) {
return mAdapter.getViewTypeCount();
}
return 1;
}
public void registerDataSetObserver(DataSetObserver observer) {
if (mAdapter != null) {
mAdapter.registerDataSetObserver(observer);
}
}
public void unregisterDataSetObserver(DataSetObserver observer) {
if (mAdapter != null) {
mAdapter.unregisterDataSetObserver(observer);
}
}
/// 这有点意思，有待发掘
public Filter getFilter() {
if (mIsFilterable) {
return ((Filterable) mAdapter).getFilter();
}
return null;
}
public ListAdapter getWrappedAdapter() {
return mAdapter;
}
}
本文出自 “林家男孩” 博客，请务必保留此出处http://bj007.blog.51cto.com/1701577/643568
