我的getView中的convertView好像没有正确实现，你能告诉我为什么吗？

Question

我的 listView 似乎加载正确，但在测试时我认为它有问题。

我正在看这个教程：http://android.amberfog.com/?p=296#more-296

我添加了以下行：

System.out.println("getView " + position + " " + convertView);

按照教程，在 logcat 中，我应该在向下滚动 listView 时看到 convertView 值，例如：

System.out(947): getView 20 android.widget.LinearLayout@437430f8

但在我的 logcat 中，我所有的 convertViews 都是 null。我什至没有滚动 listView，我的 122 行立即膨胀 - 根据 logcat 判断。所有值的形式为：

System.out: getView number is :21convertView is : null

我是不是做错了什么？

这是我的代码：

public class SelectPhoneContactAdapter extends BaseAdapter {

    //define a list made out of SelectPhoneContacts and call it theContactsList
    public List<SelectPhoneContact> theContactsList;
    //define an array list made out of SelectContacts and call it arraylist
    private ArrayList<SelectPhoneContact> arraylist;
    Context _c;

    //define a ViewHolder to hold our name and number info, instead of constantly querying
    // findviewbyid. Makes the ListView run smoother
    // ViewHolder viewHolder;

    public SelectPhoneContactAdapter(final List<SelectPhoneContact> selectPhoneContacts, Context context) {
        theContactsList = selectPhoneContacts;
        _c = context;
        this.arraylist = new ArrayList<SelectPhoneContact>();
        this.arraylist.addAll(theContactsList);

    }


    @Override
    public int getCount() {
        System.out.println("the amount in arraylist :" + theContactsList.size());
        return arraylist.size();
    }

    @Override
    public Object getItem(int i) {
        return theContactsList.get(i);
    }

    @Override
    public long getItemId(int i) {
        return i;
    }

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)

    static class ViewHolder {
        //        In each cell in the listview show the items you want to have
//        Having a ViewHolder caches our ids, instead of having to call and load each one again and again
        TextView title, phone;
        CheckBox check;
    }

    @Override
    public View getView(int i, View convertView, ViewGroup viewGroup) {
        System.out.println("getView number is :" + i + "convertView is : " + convertView);

        ViewHolder viewHolder = null;

        if (convertView == null) {

            //if there is nothing there (if it's null) inflate the view with the layout
            LayoutInflater li = (LayoutInflater) _c.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = li.inflate(R.layout.phone_inflate_listview, null);

            viewHolder = new ViewHolder();

            //      So, for example, title is cast to the name id, in phone_inflate_listview,
//        phone is cast to the id called no etc
            viewHolder.title = (TextView) convertView.findViewById(R.id.name);
            viewHolder.phone = (TextView) convertView.findViewById(R.id.no);

            viewHolder.check = (CheckBox) convertView.findViewById(R.id.checkBoxContact);
            viewHolder.check.setVisibility(View.GONE);

            //remember the state of the checkbox
            viewHolder.check.setOnCheckedChangeListener((NewContact) _c);

            convertView.setTag(viewHolder);

        } else {

            viewHolder = (ViewHolder) convertView.getTag();

        }
//        store the holder with the view
            final SelectPhoneContact data = (SelectPhoneContact) theContactsList.get(i);
            //in the listview for contacts, set the name
            viewHolder.title.setText(data.getName());
            //in the listview for contacts, set the number
            viewHolder.phone.setText(data.getPhone());

            viewHolder.check.setChecked(data.isSelected());
            viewHolder.check.setTag(data);

        return convertView;

    }
}

在我的 activity 中，我使用了一个函数来测量列表视图在加载到屏幕之前的高度，也许这是问题的一部分。不知道能不能解决，如果能解决就好了

来自我的 NewContact.java:

 @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);

            adapter = new SelectPhoneContactAdapter(selectPhoneContacts, NewContact.this);

            adapter.notifyDataSetChanged();
            listView.setAdapter(adapter);

            justifyListViewHeightBasedOnChildren(listView);

        }

justifyListViewHeightBasedOnChildren 函数：

//this is the function we call to measure the height of the listview
//we need this because there are problems with a listview within a scrollview
public static void justifyListViewHeightBasedOnChildren (ListView listView) {

    ListAdapter adapter = listView.getAdapter();

    if (adapter == null) {
        return;
    }
    ViewGroup vg = listView;
    int totalHeight = 0;
    for (int i = 0; i < adapter.getCount(); i++) {
        View listItem = adapter.getView(i, null, vg);
        listItem.measure(0, 0);
        totalHeight += listItem.getMeasuredHeight();
    }

    ViewGroup.LayoutParams par = listView.getLayoutParams();
    par.height = totalHeight + (listView.getDividerHeight() * (adapter.getCount() - 1));
    listView.setLayoutParams(par);
    listView.requestLayout();

    System.out.println("the getcount is " + adapter.getCount());
    System.out.println("the height is " + par.height);
}

Answer 1

当ListView调用getView()方法时，convertView参数是否有non-null值取决于ListView是否为试图 "recycle" 一个视图。当屏幕上之前的视图滚动（足够远） off-screen 并且 ListView 确信它暂时不需要并且可以是 re-used ("recycled") 以显示即将滚动 on-screen.

的 "new" 视图的值

这里的想法是 ListView 的所有 children 具有相同的结构；他们在相同的地方有相同的View。只有那些视图的 contents 发生了变化。因此，与其膨胀另一个视图，不如回收一个不再使用的旧视图。

不管它是如何发生的，如果你的 ListView 足够大，可以一次容纳所有 children，那么回收是不可能的。你基本上创造了一个美化 LinearLayout。这是否是一个问题完全取决于您和您的要求。但是当这种情况发生时，整个ListView（视图回收）的"point"就不会发生了。

所有这些就是说：在对 getView() 的所有 122 次调用中看到 convertView 的所有 122 个值的 null 意味着您使用的 ListView 不同于预期的。如果您的应用程序仍能完美运行，则完全没有必要更改它。但请注意，您并未在 Google 框架的预期范围内工作。

我的getView中的convertView好像没有正确实现，你能告诉我为什么吗？

My convertView in getView does not seem to be implemented properly, can you tell me why?

android

listview

convertview