学步园

          ListView是Android中最常用的控件之一. ListView中一个重要的概念就是适配器(Adapter),它是控件与数据源之间的桥梁.

常见的数据源有数组/集合(Array/List),游标(Cursor).

        1,  从数组中获取数据:

         运行结果:

        2,  从Cursor中获取数据:

        // Get a cursor with all people
        Cursor c = getContentResolver().query(People.CONTENT_URI, null, null, null, null);
        
        startManagingCursor(c);//使用的cursor的生命周期随Activity生命周期变化而变化.

        ListAdapter adapter = new SimpleCursorAdapter(this, 
                // Use a template that displays a text view
                android.R.layout.simple_list_item_1, 
                // Give the cursor to the list adatper
                c, 
                // Map the NAME column in the people database to...
                new String[] {People.NAME} ,
                // The "text1" view defined in the XML template
                new int[] {android.R.id.text1}); 
        setListAdapter(adapter);

运行结果:

            3, 使用自定义Adapter

private class SpeechListAdapter extends BaseAdapter {
        public SpeechListAdapter(Context context) {
            mContext = context;
        }

        public int getCount() {
            return mTitles.length;
        }

        public Object getItem(int position) {//每个条目对应的对象
            return position;
        }

        public long getItemId(int position) {//每个条目的id
            return position;
        }

        public View getView(int position, View convertView, ViewGroup parent) {//ListView每个item对应的view
            SpeechView sv;
            if (convertView == null) {
                sv = new SpeechView(mContext, mTitles[position],
                        mDialogue[position]);
            } else {
                sv = (SpeechView) convertView;
                sv.setTitle(mTitles[position]);
                sv.setDialogue(mDialogue[position]);
            }

            return sv;
        }
}

       结果:

一些ListView效果

                       
1,  带有分隔符的ListView.

效果所下图所示(红框表示的是分隔条):

    private class MyListAdapter extends BaseAdapter {
        public MyListAdapter(Context context) {
            mContext = context;
        }

        public int getCount() {
            return mStrings.length;
        }

        @Override
        public boolean areAllItemsEnabled() {//是否所有的item都可点击和选中
            return false;
        }

        @Override
        public boolean isEnabled(int position) {//如果字符串是以"-"开头,那么对应的item为分隔item
            return !mStrings[position].startsWith("-");
        }
        
        

        public Object getItem(int position) {
            return position;
        }

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

        public View getView(int position, View convertView, ViewGroup parent) {
            TextView tv;
            if (convertView == null) {
                tv = (TextView) LayoutInflater.from(mContext).inflate(
                        android.R.layout.simple_expandable_list_item_1, parent, false);
            } else {
                tv = (TextView) convertView;
            }
            tv.setText(mStrings[position]);
            return tv;
        }

        private Context mContext;
    }

                          2, 带收缩和展开效果的ListView

效果如下图所示:

                3 ,类似带悬浮字母效果的ListView(类似通讯录导航的效果 )         

如下图所示

下面来演示notifyDataSetChanged()方法的作用:

每次添加图片的时候都notifyDataSetChanged(),也就是数据源改变了执行notifyDataSetChanged(),可以刷新界面.

                  ListView效率问题.

我们知道一个item的显示都会调用getView()方法,并且在不停的滑动时候也会不停的调用.

下面来看一下延迟加载的效果:在不停滑动的时候用"Loading"作为显示文本,当停止滑动显示真实的文本.

            优化Adapter,提高ListView执行效率.

public View getView(int position, View convertView, ViewGroup parent) {
            // A ViewHolder keeps references to children views to avoid unneccessary calls
            // to findViewById() on each row.
            ViewHolder holder;

            // When convertView is not null, we can reuse it directly, there is no need
            // to reinflate it. We only inflate a new View when the convertView supplied
            // by ListView is null.
            if (convertView == null) {//当有老的item view的时候借用老的view,这样避免每次都去解析xml
                convertView = mInflater.inflate(R.layout.list_item_icon_text, null);

                // Creates a ViewHolder and store references to the two children views
                // we want to bind data to.
                holder = new ViewHolder();
                holder.text = (TextView) convertView.findViewById(R.id.text);
                holder.icon = (ImageView) convertView.findViewById(R.id.icon);

                convertView.setTag(holder);
            } else {
                // Get the ViewHolder back to get fast access to the TextView
                // and the ImageView.
                holder = (ViewHolder) convertView.getTag();
            }

            // Bind the data efficiently with the holder.
            holder.text.setText(DATA[position]);
            holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);

            return convertView;
        }

        static class ViewHolder {
            TextView text;
            ImageView icon;
        }
 

这样做的好处有:

            1>重用了 convertView,避免当不需要解析xml文件的时候去解析xml,填充视图.

            2>使用ViewHolder避免当不需要的时候调用findViewById()方法.

  欢迎转载,http://blog.csdn.net/johnny901114/article/details/7867934