listview有header时position不对
Posted csdn用户R
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当给ListView加了一个HeaderView后(代码如下),我们发现,onItemClick方法里的position
参数的值不是我们所期望的,比如点击ListView的第一行,我们期望的position
是0,可是实际上却是1,也就是说,它是从Header而不是从第一行开始计数的。
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.home);
mAdapter = new MyAdapter(this);
mListView = (ListView) findViewById(R.id.list);
mListView.addHeaderView(getLayoutInflater().inflate(R.layout.list_header));
mListView.setAdapter(mAdapter);
mListView.setOnClickListener(this);
@Override
public void onItemClick(AdapterView<?> parent, View v, int position, long id)
doSomething(mAdapter.getItem(position));
Google了下,发现有个老外issue过一个bug,和我遇到的问题一样,不过这个bug被RomainGuy reject掉了,理由是,你用错了,请用getAdapter。这回答的太简洁了,完全没法理解,所以只好又去仔细研究ListView的代码,终于领会他的意思了。把其中addHeaderView和setAdapter方法贴下来
/**
* Add a fixed view to appear at the top of the list. If addHeaderView is
* called more than once, the views will appear in the order they were
* added. Views added using this call can take focus if they want.
* <p>
* NOTE: Call this before calling setAdapter. This is so ListView can wrap
* the supplied cursor with one that that will also account for header
* views.
*
* @param v The view to add.
* @param data Data to associate with this view
* @param isSelectable whether the item is selectable
*/
public void addHeaderView(View v, Object data, boolean isSelectable)
if (mAdapter != null)
throw new IllegalStateException(
"Cannot add header view to list -- setAdapter has already been called.");
FixedViewInfo info = new FixedViewInfo();
info.view = v;
info.data = data;
info.isSelectable = isSelectable;
mHeaderViewInfos.add(info);
/**
* Sets the data behind this ListView.
*
* The adapter passed to this method may be wrapped by a @link WrapperListAdapter,
* depending on the ListView features currently in use. For instance, adding
* headers and/or footers will cause the adapter to be wrapped.
*
* @param adapter The ListAdapter which is responsible for maintaining the
* data backing this list and for producing a view to represent an
* item in that data set.
*
* @see #getAdapter()
*/
@Override
public void setAdapter(ListAdapter adapter)
if (null != mAdapter)
mAdapter.unregisterDataSetObserver(mDataSetObserver);
resetList();
mRecycler.clear();
if (mHeaderViewInfos.size() > 0|| mFooterViewInfos.size() > 0)
mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, adapter);
else
mAdapter = adapter;
//其它的一些代码这里省略之...
从代码和注释里都可以很清楚的得知,addHeaderView
一定要在setAdapter
之前调用,如果不这样做,addHeaderView
会抛出一个异常。android为什么要这样?这是因为,在setAdapter
的时候,会针对我遇到的这种情况(也就是添加Header后position
不正确的这种情况)做些特殊的处理。setAdapter
在内部判断了当前ListView是否有Header或者Footer,如果没有,就直接使用参数传进来的adapter;如果有,则用一个decorated的HeaderViewListAdapter
来替换参数。这个HeaderViewListAdapter
的使命,就是排除Header和Footer,让position
(当然也包括getItem, getItemId)等方法的position
参数)正确返回。
分析到这里,解决方案就出来了:在onItemClick
不要直接使用我们声明的adapter,而是用ListView里的那个decorated adapter。获取它的方法就是调用parent.getAdapter()
。当然,如果ListView没有Header和Footer,直接使用声明的adapter也没有问题,不过为了避免出错,还是统一使用decorated adapter比较好。
把onItemClick改成下面这样,就可以了
@Override
public void onItemClick(AdapterView<?> parent, View v, int position, long id)
doSomething(parent.getAdapter().getItem(position));
本文由Roy最初发表于:http://blog.chengbo.net/2012/03/09/onitemclick-return-wrong-position-when-listview-has-headerview.html,你可以在保持文章完整和保留本声明的情况下转帖、分发和印刷等。
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