Widgets高级篇(二)

本文翻译整理自： http://developer.android.com/guide/topics/appwidgets/index.html#implementing_collections

3.3、AppWidgetProvider class for app widgets with collections

 app widgets with collections像一般的app widget一样，你主要代码应该在AppWidgetProvider的onUpdate()方法中。

主要区别在于，在 app widgets with collections中，你必须对RemoteViews调用setRemoteAdapter方法。这个函数能告诉collection view能在哪里取得它的数据.。RemoteViewsService必须能返回一个RemoteViewsFactory对象。 当你调用setRemoteAdapter()方法的时候, 你必须传递一个用于启动你的RemoteViewsService的intent和一个App Widget ID用于说明对哪个app widget进行更新.

For example, here's how the StackView Widget sample implements the onUpdate() callback method to set the RemoteViewsService as the remote adapter for the app widget collection:

示例4

public void onUpdate(Context context, AppWidgetManager appWidgetManager,
int[] appWidgetIds) {
    // update each of the app widgets with the remote adapter
    for (int i = 0; i < appWidgetIds.length; ++i) {
        
        // Set up the intent that starts the StackViewService, which will
        // provide the views for this collection.
        Intent intent = new Intent(context, StackWidgetService.class);
        // Add the app widget ID to the intent extras.
        intent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetIds[i]);
        intent.setData(Uri.parse(intent.toUri(Intent.URI_INTENT_SCHEME)));
        // Instantiate the RemoteViews object for the App Widget layout.
        RemoteViews rv = new RemoteViews(context.getPackageName(), R.layout.widget_layout);
        // Set up the RemoteViews object to use a RemoteViews adapter. 
        // This adapter connects
        // to a RemoteViewsService  through the specified intent.
        // This is how you populate the data.
        rv.setRemoteAdapter(appWidgetIds[i], R.id.stack_view, intent);
        
        // The empty view is displayed when the collection has no items. 
        // It should be in the same layout used to instantiate the RemoteViews
        // object above.
        rv.setEmptyView(R.id.stack_view, R.id.empty_view);

        //
        // Do additional processing specific to this app widget...
        //
        
        appWidgetManager.updateAppWidget(appWidgetIds[i], rv);   
    }
    super.onUpdate(context, appWidgetManager, appWidgetIds);
}

3.4、RemoteViewsService class

如上面描述那样, 你的RemoteViewsService应该编写一个RemoteViewsFactory，以提供数据项的remote collection view.

具体来说，您需要执行这些步骤：

第一、新建一个RemoteViewsService的子类. RemoteViewsService是个service，通过它remote adapter可以请求并获得RemoteViews.

第二，在你RemoteViewsService的子类中, 添加一个实现了RemoteViewsFactory接口的方法.  RemoteViewsFactory 为collection view (such as ListView, GridView, and so on)和collection view的数据提供了适配接口。 在RemoteViewsFactory中，你要负责为数据集的每个数据项提供一个RemoteViews对象. RemoteViewsFactory相等于Adapter的一个精简版本。

编写RemoteViewsService的主要工作集中在RemoteViewsFactory,关于次将在下文进行介绍

3.5、RemoteViewsFactory interface

你的RemoteViewsFactory需要为app widget提供数据集的每个数据项其对应的RemoteViews对象

为此, 你需要用app widget数据项的View布局文件和数据集的数据项来合成RemoteViews对象。数据源可以为任何形式，可以是一个简单的数组，也来自于数据库。在StackView Widget示例程序中, 数据源是个WidgetItems数组. RemoteViewsFactory的主要功能就是把数据变成 RemoteViews.

在RemoteViewsFactory中，你主要需要实现onCreate() 和getViewAt()这两个方法 。

当RemoteViewsFactory首次被创建时，onCreate()方法将被调用. 

在该函数中，你应该做些初始工作，比如建立针对你的数据源的连接或光标。比如, 在StackView Widget示例程序中的onCreate()方法中，

就初始了一个WidgetItem对象数组. 当你app widget活动的时候, 系统可以通过数组索引号来访问这些WidgetItem对象。

这些WidgetItem对象中所包含的文本内容也就将被显示。

以下是StackView Widget示例程序的RemoteViewsFactory中关于onCreate()方法的部分代码:

示例5

class StackRemoteViewsFactory implements
RemoteViewsService.RemoteViewsFactory {
    private static final int mCount = 10;
    private List<WidgetItem> mWidgetItems = new ArrayList<WidgetItem>();
    private Context mContext;
    private int mAppWidgetId;

    public StackRemoteViewsFactory(Context context, Intent intent) {
        mContext = context;
        mAppWidgetId = intent.getIntExtra(AppWidgetManager.EXTRA_APPWIDGET_ID,
                AppWidgetManager.INVALID_APPWIDGET_ID);
    }

    public void onCreate() {
        // In onCreate() you setup any connections / cursors to your data source. Heavy lifting,
        // for example downloading or creating content etc, should be deferred to onDataSetChanged()
        // or getViewAt(). Taking more than 20 seconds in this call will result in an ANR.
        for (int i = 0; i < mCount; i++) {
            mWidgetItems.add(new WidgetItem(i + "!"));
        }
        ...
    }
...

RemoteViewsFactory的getViewAt()方法将返回与数据集的指定位置的数据项相对应的RemoteViews对象.下面是 StackView Widget示例程序中， 关于 RemoteViewsFactory  的部分代码。

示例6

public RemoteViews getViewAt(int position) {
   
    // Construct a remote views item based on the app widget item XML file, 
    // and set the text based on the position.
    RemoteViews rv = new RemoteViews(mContext.getPackageName(), R.layout.widget_item);
    rv.setTextViewText(R.id.widget_item, mWidgetItems.get(position).text);

    ...
    // Return the remote views object.
    return rv;
}