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addHeaderViewsetAdapter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getItemgetItemId)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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