ListActivity 和 Activity 的奇怪行为

Question

I'm implementing an application for android and I run into memory issues while populating a list view with data from the internet. A strange error that occurs seems to be caused by the lack of recycling of the rows as it should normally happen as it is stated at Google I/O 2009 .

When I run the code at http://android.amberfog.com/?p=296 , everything is running smoothly, the row views are recycled and the listView is optimally used.

I now want to use the listView within another activity that will have much more things inside, therefore a class that extends just ListActivity, is not enough. So, I have an Activity that has the following code:

public class MultipleItemsList extends Activity {
    private Context mContext;
    private MyCustomAdapter mAdapter;
    private ListView listView;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mContext = this;

        listView = (ListView) findViewById(R.id.listView);

        mAdapter = new MyCustomAdapter(mContext);

        for (int i = 1; i < 50; i++) {
            mAdapter.addItem("item " + i);
        }

        listView.setAdapter(mAdapter);
    }  
}

The main.xml is nothing fancy also:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <TextView  
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        android:text="@string/hello"/>

    <ListView
        android:id="@+id/listView"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

The ListActivity that the previous link proposes is the following:

public class MultipleItemsList extends ListActivity {
    private Context mContext;
    private MyCustomAdapter mAdapter;
    private ListView listView;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mContext = this;

        mAdapter = new MyCustomAdapter(mContext);

        for (int i = 1; i < 50; i++) {
            mAdapter.addItem("item " + i);
        }
        setListAdapter(mAdapter);
    }
}

The adapter is the following in both cases:

public class MyCustomAdapter extends BaseAdapter {
    private static final int TYPE_ITEM = 0;
    private static final int TYPE_SEPARATOR = 1;
    private static final int TYPE_MAX_COUNT = TYPE_SEPARATOR + 1;

    private ArrayList<String> mData = new ArrayList<String>();
    private LayoutInflater mInflater;

    private TreeSet<Integer> mSeparatorsSet = new TreeSet<Integer>();

    public static class ViewHolder {
        public TextView textView;
    }

    public MyCustomAdapter(Context context) {
        mInflater = LayoutInflater.from(context);
    }

    public void addItem(final String item) {
        mData.add(item);
        notifyDataSetChanged();
    }

    public void addSeparatorItem(final String item) {
        mData.add(item);
        // save separator position
        mSeparatorsSet.add(mData.size() - 1);
        notifyDataSetChanged();
    }

    @Override
    public int getItemViewType(int position) {
        return mSeparatorsSet.contains(position) ? TYPE_SEPARATOR : TYPE_ITEM;
    }

    @Override
    public int getViewTypeCount() {
        return TYPE_MAX_COUNT;
    }

    @Override
    public int getCount() {
        return mData.size();
    }

    @Override
    public String getItem(int position) {
        return mData.get(position);
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder = null;
        int type = getItemViewType(position);
        Log.d("myCA", "getView " + position + " " + convertView + " type = " + type);
        if (convertView == null) {
            holder = new ViewHolder();
            switch (type) {
                case TYPE_ITEM:
                    convertView = mInflater.inflate(R.layout.item1, null);
                    holder.textView = (TextView)convertView.findViewById(R.id.text);
                    break;
                case TYPE_SEPARATOR:
                    convertView = mInflater.inflate(R.layout.item2, null);
                    holder.textView = (TextView)convertView.findViewById(R.id.textSeparator);
                    break;
            }
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder)convertView.getTag();
        }
        holder.textView.setText(mData.get(position));
        return convertView;
    }
}

So, my question is why in the second case of the ListActivity the view recycling takes place without problems, while at the implementation of the Activity, recycling gets screwed up?

The Log shows that when the ListActivity is used, everything is recycled correctly:

    07-13 10:14:25.277: DEBUG/myCA(2336): getView 0 null type = 0
    07-13 10:14:25.277: DEBUG/myCA(2336): getView 1 null type = 0
    07-13 10:14:25.277: DEBUG/myCA(2336): getView 2 null type = 0
    07-13 10:14:25.277: DEBUG/myCA(2336): getView 3 null type = 0
    07-13 10:14:25.287: DEBUG/myCA(2336): getView 4 null type = 0
    07-13 10:14:25.287: DEBUG/myCA(2336): getView 5 null type = 0
    07-13 10:14:27.887: DEBUG/myCA(2336): getView 6 null type = 0
    07-13 10:14:28.047: DEBUG/myCA(2336): getView 7 android.widget.LinearLayout@40522c30 type = 0
    07-13 10:14:28.267: DEBUG/myCA(2336): getView 8 android.widget.LinearLayout@405236b8 type = 0
...
...
...

At my implementation of Activity, I see the following:

07-13 10:11:47.517: DEBUG/myCA(2296): getView 0 null type = 0
07-13 10:11:47.517: DEBUG/myCA(2296): getView 1 android.widget.LinearLayout@405221e8 type = 0
07-13 10:11:47.517: DEBUG/myCA(2296): getView 2 android.widget.LinearLayout@405221e8 type = 0
07-13 10:11:47.517: DEBUG/myCA(2296): getView 3 android.widget.LinearLayout@405221e8 type = 0
07-13 10:11:47.527: DEBUG/myCA(2296): getView 4 android.widget.LinearLayout@405221e8 type = 0
07-13 10:11:47.527: DEBUG/myCA(2296): getView 5 android.widget.LinearLayout@405221e8 type = 0
07-13 10:11:47.547: DEBUG/myCA(2296): getView 0 android.widget.LinearLayout@405221e8 type = 0
07-13 10:11:47.547: DEBUG/myCA(2296): getView 1 null type = 0
07-13 10:11:47.547: DEBUG/myCA(2296): getView 2 null type = 0
07-13 10:11:47.557: DEBUG/myCA(2296): getView 3 null type = 0
...
...
...

where there is clearly problem with the recycling.

Am I missing something that would make the listView behave properly when the parent activity is just a simple activity and not a ListActivity? Has anyone come across something like that in the past?

Thanks for your time.

Answer 1

Both Activity and ListActivity should be fine. I believe you're leaking the entire activity through the mContext reference. Remove it and see what happens!