今天在做项目的时候,遇到一个问题,记录下来。
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。
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@Override
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protected void onCreate(Bundle savedInstanceState) {
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super.onCreate(savedInstanceState);
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setContentView(R.layout.home);
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mAdapter = new MyAdapter(this);
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mListView = (ListView) findViewById(R.id.list);
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mListView.addHeaderView(getLayoutInflater().inflate(R.layout.list_header));
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mListView.setAdapter(mAdapter);
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mListView.setOnClickListener(this);
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}
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@Override
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public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
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doSomething(mAdapter.getItem(position));
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}
Google了下,发现有个老外issue过一个,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
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/**
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* Add a fixed view to appear at the top of the list. If addHeaderView is
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* called more than once, the views will appear in the order they were
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* added. Views added using this call can take focus if they want.
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*
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* NOTE: Call this before calling setAdapter. This is so ListView can wrap
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* the supplied cursor with one that that will also account for header
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* views.
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*
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* @param v The view to add.
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* @param data Data to associate with this view
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* @param isSelectable whether the item is selectable
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*/
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public void addHeaderView(View v, Object data, boolean isSelectable) {
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if (mAdapter != null) {
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throw new IllegalStateException(
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"Cannot add header view to list -- setAdapter has already been called.");
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}
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FixedViewInfo info = new FixedViewInfo();
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info.view = v;
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info.data = data;
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info.isSelectable = isSelectable;
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mHeaderViewInfos.add(info);
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}
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/**
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* Sets the data behind this ListView.
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*
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* The adapter passed to this method may be wrapped by a {@link WrapperListAdapter},
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* depending on the ListView features currently in use. For instance, adding
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* headers and/or footers will cause the adapter to be wrapped.
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*
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* @param adapter The ListAdapter which is responsible for maintaining the
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* data backing this list and for producing a view to represent an
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* item in that data set.
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*
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* @see #getAdapter()
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*/
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@Override
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public void setAdapter(ListAdapter adapter) {
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if (null != mAdapter) {
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mAdapter.unregisterDataSetObserver(mDataSetObserver);
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}
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resetList();
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mRecycler.clear();
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if (mHeaderViewInfos.size() > 0|| mFooterViewInfos.size() > 0) {
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mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, adapter);
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} else {
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mAdapter = adapter;
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}
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//其它的一些代码这里省略之...
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}
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
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@Override
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public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
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doSomething(parent.getAdapter().getItem(position));
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}
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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