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listview添加footerview不生效

发表于 分类于 阅读次数： Valine： 3.1k 3 分钟

问题

使用listview添加footerview，始终显示不出来。

上网一查，Android-4.4之前添加footerview一定要在setAdapter之前，换句话说，addFooterView之后需要重新setAdapter才能生效
之前的代码是这样的：

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if (mListView.getFooterViewsCount() == 0) {
     mListView.addFooterView(createMoreCityView());
}

改成如下即可

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if (mListView.getFooterViewsCount() == 0) {
    mListView.addFooterView(createMoreCityView());
    if (SystemUtils.isBelowKitkat()) {
        mListView.setAdapter(mCityAdapter);
    }
}

原因

在Android 4.4之前，ListView添加footerview大致代码是这样的(下方是android 4.2.2代码)：

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/**
 * Add a fixed view to appear at the bottom of the list. If addFooterView 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 will also account for header and footer
 * views.
 *
 * @param v The view to add.
 * @param data Data to associate with this view
 * @param isSelectable true if the footer view can be selected
 */
public void addFooterView(View v, Object data, boolean isSelectable) {
    // NOTE: do not enforce the adapter being null here, since unlike in
    // addHeaderView, it was never enforced here, and so existing apps are
    // relying on being able to add a footer and then calling setAdapter to
    // force creation of the HeaderViewListAdapter wrapper
    FixedViewInfo info = new FixedViewInfo();
    info.view = v;
    info.data = data;
    info.isSelectable = isSelectable;
    mFooterViewInfos.add(info);
    // in the case of re-adding a footer view, or adding one later on,
    // we need to notify the observer
    if (mAdapter != null && mDataSetObserver != null) {
        mDataSetObserver.onChanged();
    }
}

Note明确提示需要在setAdater之前添加footerview，在setAdater之后，会重新生成一个HeaderViewListAdapter来展示footerview，否则不会生效。

而在Android 4.4之后，ListView添加footerview代码大致为（下方为android 7.0.0代码）：

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/**
 * Add a fixed view to appear at the bottom of the list. If addFooterView 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 true if the footer view can be selected
 */
public void addFooterView(View v, Object data, boolean isSelectable) {
    final FixedViewInfo info = new FixedViewInfo();
    info.view = v;
    info.data = data;
    info.isSelectable = isSelectable;
    mFooterViewInfos.add(info);
    mAreAllItemsSelectable &= isSelectable;
    // Wrap the adapter if it wasn't already wrapped.
    if (mAdapter != null) {
        if (!(mAdapter instanceof HeaderViewListAdapter)) {
            mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, mAdapter);
        }
        // In the case of re-adding a footer view, or adding one later on,
        // we need to notify the observer.
        if (mDataSetObserver != null) {
            mDataSetObserver.onChanged();
        }
    }
}

就不会有这个问题了。

结论

Android 4.4之前，addFooterView之后需要（重新）设置Adapter才能生效
Android 4.4及以后，addFooterView可以在任意地方调用