当ListView有Header时，onItemClick里的position不正确

今天在做项目的时候，遇到一个问题，记录下来。

当我们给ListView添加一个HeaderView后（代码如下），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，可是却是1，也就是说，它是从Header开始计数的。

@OverrideprotectedvoidonCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);     setContentView(R.layout.home);     mAdapter = newMyAdapter(this);     mListView = (ListView) findViewById(R.id.list);    mListView.addHeaderView(getLayoutInflater().inflate(R.layout.list_header));    mListView.setAdapter(mAdapter);    mListView.setOnClickListener(this);} @OverridepublicvoidonItemClick(AdapterView<?> parent, View v, intposition, longid) {    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。回答的太简洁了，完全没法理解，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 */publicvoidaddHeaderView(View v, Object data, booleanisSelectable) {    if(mAdapter != null) {        thrownewIllegalStateException(                "Cannot add header view to list -- setAdapter has already been called.");    }     FixedViewInfo info = newFixedViewInfo();    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() */@OverridepublicvoidsetAdapter(ListAdapter adapter) {    if(null!= mAdapter) {        mAdapter.unregisterDataSetObserver(mDataSetObserver);    }     resetList();    mRecycler.clear();     if(mHeaderViewInfos.size() > 0|| mFooterViewInfos.size() > 0) {        mAdapter = newHeaderViewListAdapter(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，如果不是，addHeaderView会抛出一个异常。Android为什么要这样做？因为，在setAdapter的时候，会针对我遇到的这种情况（也就是说，position不正确）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）正确返回。

分析到这里，解决方案就出来了：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，不过为了方便、避免以后出错，还是统一使用decorated adapter比较好。

把onItemClick改成下面这样，就可以了

@OverridepublicvoidonItemClick(AdapterView<?> parent, View v, intposition, longid) {    doSomething(parent.getAdapter().getItem(position));}

android listview headerView