当ListView有Header或footer时，onItemClick里的position不正确，可以用getAdapter()

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当ListView有Header或footer时，onItemClick里的position不正确，可以用getAdapter()

2012-07-27 17:10 94人阅读评论(0) 收藏举报

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@Override
protectedvoid 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, 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

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/**
 * 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, booleanisSelectable) {
    if(mAdapter != null) {
        thrownew 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

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@Override
public void onItemClick(AdapterView<?> parent, View v, int position, longid) {
    doSomething(parent.getAdapter().getItem(position));
}