Android列表视图(List View)

Android列表视图(ListView)

 

ListView是一个显示滚动项列表的示视图组(viewgroup)，通过使用适配器(Adapter)把这些列表项自动插入到列表中。适配器比如从一个数组或是数据库查询获取到数据，然后转换每一项成为可放入到列表的视图。

 

列表的显示需要三个元素：

(1)    ListView：用来展示列表的view。

(2)    适配器：用来把数据映射到ListView上。

(3)    数据：具体的将被映射的字符串、图片或是基本组件。

 

 图1

对于我们如何使用适配器来动态插入view，参考链接：

http://developer.android.com/guide/topics/ui/declaring-layout.html#AdapterViews

 

1.      使用加载器(Using a Loader)

为了实现异步加载数据，且为了避免在查询时阻塞APP主线程，从Android3.0开始引入CursorLoader，这是一种查询Cursor的标准方式。当CursorLoader接收到Cursor结果(查询结束)，LoaderCallbacks接收到对onLoadFinished()方法的回调，此方法使用新的Cursor来更新适配器，然后列表视图显示这个结果。

 

虽然CursorLoader的API是从Android3.0(API 11)开始引入的，但可以通过使用支持的库来使用：http://developer.android.com/tools/extras/support-library.html，但要求Android系统版本在1.6及之后的版本。

 

public class ListViewLoader extends ListActivity
        implements LoaderManager.LoaderCallbacks<Cursor> {

    // This is the Adapter being used to display the list's data
    SimpleCursorAdapter mAdapter;

    // These are the Contacts rows that we will retrieve
    static final String[] PROJECTION = new String[] {ContactsContract.Data._ID,
            ContactsContract.Data.DISPLAY_NAME};

    // This is the select criteria
    static final String SELECTION = "((" +
            ContactsContract.Data.DISPLAY_NAME + " NOTNULL)AND (" +
            ContactsContract.Data.DISPLAY_NAME + " != ''))";

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

        // Create a progress bar to display whilethe list loads
        ProgressBar progressBar = new ProgressBar(this);
        progressBar.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT,
                LayoutParams.WRAP_CONTENT, Gravity.CENTER));
        progressBar.setIndeterminate(true);
        getListView().setEmptyView(progressBar);

        // Must add the progress bar to the root ofthe layout
        ViewGroup root = (ViewGroup) findViewById(android.R.id.content);
        root.addView(progressBar);

        // For the cursor adapter, specify whichcolumns go into which views
        String[] fromColumns = {ContactsContract.Data.DISPLAY_NAME};
        int[] toViews = {android.R.id.text1}; // The TextViewin simple_list_item_1

        // Create an empty adapter we will use todisplay the loaded data.
        // We pass null for the cursor, then updateit in onLoadFinished()
        mAdapter = new SimpleCursorAdapter(this,
                android.R.layout.simple_list_item_1, null,
                fromColumns, toViews, 0);
        setListAdapter(mAdapter);

        // Prepare the loader.  Eitherre-connect with an existing one,
        // or start a new one.
        getLoaderManager().initLoader(0, null, this);
    }

    // Called when a new Loader needs to be created
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {
        // Now create and return a CursorLoaderthat will take care of
        // creating a Cursor for the data beingdisplayed.
        return new CursorLoader(this, ContactsContract.Data.CONTENT_URI,
                PROJECTION, SELECTION, null, null);
    }

    // Called when a previously created loader has finished loading
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
        // Swap the new cursor in.  (Theframework will take care of closing the
        // old cursor once we return.)
        mAdapter.swapCursor(data);
    }

    // Called when a previously created loader is reset, making the dataunavailable
    public void onLoaderReset(Loader<Cursor> loader) {
        // This is called when the last Cursorprovided to onLoadFinished()
        // above is about to be closed.  We needto make sure we are no
        // longer using it.
        mAdapter.swapCursor(null);
    }

    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        // Do something when a list item is clicked
    }
}

 

链接:

Android开发者：

http://developer.android.com/guide/topics/ui/layout/listview.html

 

Android之ListView原理学习与优化总结

http://mzh3344258.blog.51cto.com/1823534/889879

 

androidListView详解

http://www.cnblogs.com/allin/archive/2010/05/11/1732200.html

Android的CursorLoader用法小结

http://www.linuxidc.com/Linux/2013-05/84572.htm