Android ListView addHeaderView()的调用顺序

从api文档上看,4.4以下版本 addHeaderView()必须在setAdapter()之前调用,4.4以后的版本中,addHeaderView()可以在任何地方调用

/**
* Add a fixed view to appear at the top of the list. If this method 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: When first introduced, this method could only be called before
* setting the adapter with {@link #setAdapter(ListAdapter)}. Starting with
* {@link android.os.Build.VERSION_CODES#KITKAT}, this method may be
* called at any time. If the ListView's adapter does not extend
* {@link HeaderViewListAdapter}, it will be wrapped with a supporting
* instance of {@link WrapperListAdapter}.
*
* @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) {...}

4.4之前addHeader()代码

public void addHeaderView(View v, Object data, boolean isSelectable) {

// 这里的一个判断,如果有Adapter直接抛异常
if (mAdapter != null && ! (mAdapter instanceof HeaderViewListAdapter)) {
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);

// in the case of re-adding a header view, or adding one later on,
// we need to notify the observer
if (mAdapter != null && mDataSetObserver != null) {
mDataSetObserver.onChanged();
}
}

4.4之后的addHeader()

public void addHeaderView(View v, Object data, boolean isSelectable) {
final FixedViewInfo info = new FixedViewInfo();
info.view = v;
info.data = data;
info.isSelectable = isSelectable;
mHeaderViewInfos.add(info);
mAreAllItemsSelectable &= isSelectable;

// Wrap the adapter if it wasn't already wrapped.
if (mAdapter != null) {
if (!(mAdapter instanceof HeaderViewListAdapter)) {
// adapter 都会转换成HeaderViewListAdapter
mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, mAdapter);
}

// In the case of re-adding a header view, or adding one later on,
// we need to notify the observer.
if (mDataSetObserver != null) {
mDataSetObserver.onChanged();
}
}
}