UI组件之AdapterView及其子类（五）ListView组件和ListActivity

ListView组件是一个显示组件，继承AdapterView基类，前面已经介绍了分别使用ArrayAdapter，SimpleAdapter，扩展BaseAdapter来为LisView提供列表项http://blog.csdn.net/tuke_tuke/article/details/50527018。在当中都要在xml文件里定义ListView组件，然后再Activity.java文件里通过findViewById获取组件设置定义好的adapter就可以。

可是ListActivity是直接继承Activity的，在ListActivity的源代码中已经定义了一个ListView组件属性。ListActivity的子类无需调用setContentView()来显示某个界面，ListActivity的效果就是整个Activity就是一个列表，没有其它的组件。在使用ListActivity时，仅仅须要继承ListActivity，直接传入一个内容Adapter。

ListActivity就是一个列表.

MainActivity.java

<span style="font-size:24px;">public class MainActivity extends ListActivity {//继承ListActivity

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
       
        //无需使用布局文件，-相当于它的布局文件里仅仅有一个ListView
        String[] s={"孙悟空","猪八戒","唐僧"};
        //创建ArrayAdapter对象,这里使用的是android提供的布局文件
        //ArrayAdapter<String>  ad=new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,s);
       //以下是使用自己定义的一个列表项布局
        ArrayAdapter<String>  ad=new ArrayAdapter<String>(this,R.layout.array_item,s);
        
        //设置适配器
        setListAdapter(ad);
    }</span>

1，继承ListActivity

2。定义适当的Adapter

3。调用setListAdapter方法设置Adapter

ListActivity的部分源代码:

public class ListActivity extends Activity {
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected ListAdapter mAdapter;
    /**
     * This field should be made private, so it is hidden from the SDK.
     * {@hide}
     */
    protected ListView mList;

    private Handler mHandler = new Handler();
    private boolean mFinishedStart = false;

    private Runnable mRequestFocus = new Runnable() {
        public void run() {
            mList.focusableViewAvailable(mList);
        }
    };

    /**
     * This method will be called when an item in the list is selected.
     * Subclasses should override. Subclasses can call
     * getListView().getItemAtPosition(position) if they need to access the
     * data associated with the selected item.
     *
     * @param l The ListView where the click happened
     * @param v The view that was clicked within the ListView
     * @param position The position of the view in the list
     * @param id The row id of the item that was clicked
     */
    protected void onListItemClick(ListView l, View v, int position, long id) {
    }

    /**
     * Ensures the list view has been created before Activity restores all
     * of the view states.
     *
     *@see Activity#onRestoreInstanceState(Bundle)
     */
    @Override
    protected void onRestoreInstanceState(Bundle state) {
        ensureList();
        super.onRestoreInstanceState(state);
    }

    /**
     * @see Activity#onDestroy()
     */
    @Override
    protected void onDestroy() {
        mHandler.removeCallbacks(mRequestFocus);
        super.onDestroy();
    }

    /**
     * Updates the screen state (current list and other views) when the
     * content changes.
     *
     * @see Activity#onContentChanged()
     */
    @Override
    public void onContentChanged() {
        super.onContentChanged();
        View emptyView = findViewById(com.android.internal.R.id.empty);
        mList = (ListView)findViewById(com.android.internal.R.id.list);
        if (mList == null) {
            throw new RuntimeException(
                    "Your content must have a ListView whose id attribute is " +
                    "‘android.R.id.list‘");
        }
        if (emptyView != null) {
            mList.setEmptyView(emptyView);
        }
        mList.setOnItemClickListener(mOnClickListener);
        if (mFinishedStart) {
            setListAdapter(mAdapter);
        }
        mHandler.post(mRequestFocus);
        mFinishedStart = true;
    }

    /**
     * Provide the cursor for the list view.
     */
    public void setListAdapter(ListAdapter adapter) {
        synchronized (this) {
            ensureList();
            mAdapter = adapter;
            mList.setAdapter(adapter);
        }
    }

    /**
     * Set the currently selected list item to the specified
     * position with the adapter‘s data
     *
     * @param position
     */
    public void setSelection(int position) {
        mList.setSelection(position);
    }

    /**
     * Get the position of the currently selected list item.
     */
    public int getSelectedItemPosition() {
        return mList.getSelectedItemPosition();
    }

    /**
     * Get the cursor row ID of the currently selected list item.
     */
    public long getSelectedItemId() {
        return mList.getSelectedItemId();
    }

    /**
     * Get the activity‘s list view widget.
     */
    public ListView getListView() {
        ensureList();
        return mList;
    }

    /**
     * Get the ListAdapter associated with this activity‘s ListView.
     */
    public ListAdapter getListAdapter() {
        return mAdapter;
    }

    private void ensureList() {
        if (mList != null) {
            return;
        }
        setContentView(com.android.internal.R.layout.list_content_simple);

    }

    private AdapterView.OnItemClickListener mOnClickListener = new AdapterView.OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View v, int position, long id)
        {
            onListItemClick((ListView)parent, v, position, id);
        }
    };
}