Android setAdapter addHeaderView 報錯解決方案

原創

2020-02-21 18:24

報錯內容：Cannot add header view to list – setAdapter has already been called

1、在sdk <=16的版本中,ListView的addHeaderView()方法是這樣的:

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

        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();
        }
    }

如果調用此方法之前沒有調用setAdapter()方法,那麼mAdapter就爲null,也就不會報錯,如果調用了setAdapter()方法爲ListView設置了Adapter,那麼就會報錯拋出一個異常.

2、而sdk>16的版本中,addHeaderView()方法是這樣的:

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);

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

也就是說,如果在調用addHeaderView()方法之前就爲ListView設置了Adapter,那麼ListView會根據你設置的Adapter自動構建一個HeaderViewListAdapter,也就不會報錯了.

3、也就是說，如果setAdapter()方法在addHeaderView()方法之前調用了，那麼在sdk<=16版本的手機上運行就會報錯–Cannot add header view to list – setAdapter has already been called,知道了問題產生的原因,那麼要解決也就很簡單了.

方法一、如果沒有特殊的必要，那麼就先爲你的ListView addHeaderView()，然後再setAdapter()吧.

方法二、如果業務一定需要先setAdapter()，那麼就可以爲ListView添加一個高度爲0的HeaderView/FooterView就可以解決這個問題了，代碼如下：

View emptyfooterView = new View(this);
LayoutParams lp = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
emptyfooterView.setLayoutParams(lp);
listView.addFooterView(emptyfooterView, null, false);

添加了一個空的HeaderView/FooterView之後，setAdapter()和addHeaderView()的先後順序就不重要了.