Android：getView() 在自定义适配器中调用了两次

Question

我正在将自定义 SimpleCursorAdapter 设置为 ListView。出于某种原因，对于数据库中的每个项目，FriendAdapter 的 getView() 都会被调用两次。经过一番调查（我的contact_list.xml中没有wrap_content），我仍然无法弄清楚原因。

可能是什么原因？有人可以帮忙吗？

谢谢

ContactSelection.java

public class ContactSelection extends ListActivity {

    private WhipemDBAdapter mDbHelper;  

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

        mDbHelper = new WhipemDBAdapter(this);
        mDbHelper.open();     

        setContentView(R.layout.contact_list);        

        Cursor c = mDbHelper.fetchAllFriends();
        startManagingCursor(c);     
        String[] from = new String[] {};
        int[] to = new int[] {};

        setListAdapter(new FriendAdapter(this, R.layout.contact_row, c, from, to));

        getListView().setItemsCanFocus(false);
        getListView().setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);
    }

    @Override
    protected void onResume() {
        super.onResume();
        mDbHelper.open();
    }

    @Override
    protected void onPause() {
        super.onPause();
        mDbHelper.close();
    }
}

FriendAdapter.java

public class FriendAdapter extends SimpleCursorAdapter implements OnClickListener {

    private Context mContext;
    private int mLayout;
    private Cursor mCursor;
    private int mNameIndex;
    private int mIdIndex;
    private LayoutInflater mLayoutInflater; 
    private final ImageDownloader imageDownloader = new ImageDownloader();  

    private final class ViewHolder {
        public TextView name;
        public ImageView image;
        public CheckBox checkBox;
    }

    public FriendAdapter(Context context, int layout, Cursor c, String[] from, int[] to) {
        super(context, layout, c, from, to);

        this.mContext = context;
        this.mLayout = layout;
        this.mCursor = c;
        this.mNameIndex = mCursor.getColumnIndex(WhipemDBAdapter.KEY_NAME);
        this.mIdIndex = mCursor.getColumnIndex(WhipemDBAdapter.KEY_FB_ID);
        this.mLayoutInflater = LayoutInflater.from(context);        
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        if (mCursor.moveToPosition(position)) {
            ViewHolder viewHolder;

            if (convertView == null) {
                convertView = mLayoutInflater.inflate(mLayout, null);

                viewHolder = new ViewHolder();
                viewHolder.name = (TextView) convertView.findViewById(R.id.contact_name);
                viewHolder.image = (ImageView) convertView.findViewById(R.id.contact_pic);
                viewHolder.checkBox = (CheckBox) convertView.findViewById(R.id.checkbox);
                viewHolder.checkBox.setOnClickListener(this);

                convertView.setTag(viewHolder);
            }
            else {
                viewHolder = (ViewHolder) convertView.getTag();
            }

            String name = mCursor.getString(mNameIndex);
            String fb_id = mCursor.getString(mIdIndex);         
            boolean isChecked = ((GlobalVars) mContext.getApplicationContext()).isFriendSelected(fb_id);

            viewHolder.name.setText(name);
            imageDownloader.download("http://graph.facebook.com/"+fb_id+"/picture", viewHolder.image);

            viewHolder.checkBox.setTag(fb_id);
            viewHolder.checkBox.setChecked(isChecked);
        }

        return convertView;
    }

    @Override
    public void onClick(View v) {
        CheckBox cBox = (CheckBox) v;
        String fb_id = (String) cBox.getTag();

        if (cBox.isChecked()) {
            if (!((GlobalVars) mContext.getApplicationContext()).isFriendSelected(fb_id))
                ((GlobalVars) mContext.getApplicationContext()).addSelectedFriend(fb_id);
        } else {
            if (((GlobalVars) mContext.getApplicationContext()).isFriendSelected(fb_id))
                ((GlobalVars) mContext.getApplicationContext()).removeSelectedFriend(fb_id);
        }

    }
}

contact_row.xml

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

    <ImageView
        android:id="@+id/contact_pic"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/contact_name"        
        android:textSize="10sp"
        android:singleLine="true"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <CheckBox
        android:id="@+id/checkbox"
        android:layout_alignParentRight="true"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

contact_list.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="horizontal"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   >
    <ListView
        android:id="@+id/android:list"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />
    <TextView
        android:id="@+id/android:empty"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:text="No items"/>
</LinearLayout>

Answer 1

这是正常的，当您有一个带有height=wrap_content（以及其他）的列表视图时可能会发生：

看最后一个帖子：http://groups.google.com/group/android-developers/browse_thread/thread/4c4aedde22fe4594

Answer 2

我用过这个。 getView 运行两次，但如果你检查convertView 是否为null，里面的代码将运行一次。

public View getView(int position, View convertView, ViewGroup parent) {
    View superView = super.getView(position, convertView, parent);
    if (convertView == null)
    {
         // Customize superView here

    }
    return superView;
}

Answer 3

对我来说，视图似乎是用相同的方法创建了两次。一个在“if(convertView==null)”中，另一个在“else”中。如果我在其中一次 if 语句中什么都不做，那么它只会创建一次。似乎该方法本身只被调用了一次。

Answer 4

为了每行只调用一次getView，您需要调用super.getView，然后更改返回的视图。是这样的

public View getView(int position, View convertView, ViewGroup parent) {
    View superView = super.getView(position, convertView, parent);
    if (mCursor.moveToPosition(position)) {
         // Customize superView here

    }
    return superView;
}