Androidリストウィジェット開発詳細

久しぶりのブログ更新なので、今回はAndroidのリストウィジェットの実装方法を勉強します。

このページをアプリの中に実装すれば、Androidの基礎を少しかじった子供なら誰でも簡単に書けると思います。しかし、Widgetの中に入れるとなると、そう簡単にはいかないかもしれません。なぜなら、Widgetは我々のアプリのプロセスではなく、システムのSystemServerのプロセスで実行されるからです。Whf!が我々のAppのプロセスにないことに驚かれるかもしれませんね。ということは、アプリでできるような View コントロールの操作はできないということでしょうか？答えは「イエス」です。しかし、あまり心配しないでください。リモートプロセスでインターフェイスを更新するために、Google dad は私たちのために特別に RemoteViews クラスを提供してくれています。名前から、RemoteViewsはViewだと思われるかもしれませんが、そうではなく、RemoteViewsは単なるView構造体なのです。リモートプロセス内のインターフェイスを表示・更新することができます。今日実装するリストウィジェットは、RemoteVeiwをベースにしています。
では、次にデスクトップウィジェットの実装方法を学びましょう。まず、ウィジェットを実装するためのいくつかのコアステップをリストアップします。

• ウィジェットページのレイアウト
• ウィジェットの設定情報
• AppWidgetProviderを理解する
• リスト適応のためのRemoteViewsFactory
• クリックのイベント処理

I. ウィジェットインターフェースの実装

1. ウィジェットページのレイアウト まず、以下の内容でレイアウトファイルlayout_widget.xmlを作成します。

レイアウトのListViewコントロールを見ると、今の時代にListViewを使うなんてと笑ってしまいますが、RecyclerViewがいいんじゃないでしょうか？そう、読んで字の如く、サポートされていないのです。Widgetで好きなものを使うことはできないし、ネイティブで使うのが不安なら自作でコントロールすることもできない。申し訳ありませんが、ウィジェットはそれをサポートしていません。つまり、ウィジェットには多くの制限があるのです。では、ウィジェットでサポートされているコントロールを見てみましょう。

RemoteViewsオブジェクト（ひいてはApp Widget）は、以下のレイアウトクラスをサポートすることができます。
フレームレイアウト
リニアレイアウト
RelativeLayout
グリッドレイアウト
そして、以下のウィジェットクラス。
アナログ時計
ボタン
クロノメーター
画像ボタン
画像ビュー
プログレスバー
テキストビュー
ビューフリッパー
リストビュー
GridView
スタックビュー
AdapterViewFlipper
これらのクラスの子孫はサポートされていません。

上記の Views のリストに加え、Android ネイティブの Views やカスタム Views を含む他のすべての Views は Widgets ではサポートされていません。したがって、ウィジェットページの制限に基づくクールなアニメーションとは、基本的におさらばです。

II. ウィジェット設定情報

設定情報は、主にウィジェットの幅や高さ、ズームモード、更新間隔など、いくつかのプロパティを設定するためのものです。res/xmlディレクトリに、好きな名前で新しいwidget_provider.xmlファイルを作成する必要があります。このファイルの内容は、以下のとおりです（参考用）。

The configuration information in the above file is described below.
minHeight, minWidth
 Defines the minimum height and minimum width of the widget (the widget can be resized by stretching).
previewImage
 Defines the icon that will be displayed when the widget is added.
initialLayout
 Defines the layout used by the widget.
updatePeriodMillis
 Defines the period, in milliseconds, at which the widget will be automatically updated.
resizeMode
 Specifies the resizing rules for the widget. Possible values are: "horizontal", "vertical", "none". "horizontal" means the widget can be stretched horizontally, "vertical" means the widget can be stretched vertically, "none" means the widget cannot be stretched; the default value is "none".
widgetCategory
 Specifies where the widget can be displayed: whether it can be displayed on the home screen or the lock screen or both. It takes the following values: "home_screen" and "keyguard", introduced in Android 4.2.


 Finally, we need to reference this file when registering the AppWidgetProvider in AndroidManifest, using the following.

     ...
    
III. Understanding the AppWidgetProvider class
Let's take a brief look at AppWidgetProvider, a class whose functionality is implemented through AppWidgetProvider. If we follow the source code, we can see that it inherits from the BroadcastReceiver class, which is a broadcast receiver. We mentioned above that RemoteViews is running in the SystemServer process, so we can assume that the widget events are broadcasted. Adding, deleting, updating, enabling, disabling, etc. of widgets are all done in AppWidgetProvider by accepting broadcasts. Look at a few methods in AppWidgetProvider.
onUpdate() This method is called when a widget is added or updated. We mentioned above that we can update a widget periodically by configuring updatePeriodMillis, but when we declare android:configure in the widget's configuration file, the onUpdate method is not called when the widget is added.
onEnable() This method is called when the user adds a widget for the first time.
onAppWidgetOptionsChanged() This method is called when a widget is added or when the size of the widget is changed. In this method we can also selectively show or hide certain controls depending on the size of the widget.
onDeleted(Context, int[]) Called when a control is deleted
onEnabled(Context) Called when the first widget is added. If the user adds two of these widgets, then onEnabled will only be called when the first one is added.
onDisabled(Context) This method is called when the last instance of the widget is removed. In this method we can do some cleanup work, such as deleting the temporary database, etc.
onReceive(Context, Intent) Called when a broadcast is received.
Of the above methods, we need to focus on the onUpdate() method and the onReceive() method. Because the onUpdate() method is called when the widget is added, we can add some interaction events to the widget at this point, such as clicks. Since we are going to implement a list widget in this article, we also need RemoteViews. So we also need the RemoteViewsFactory class to adapt the list data.
Let's look at the code in the ListWidgetProvider class.
public class ListWidgetProvider extends AppWidgetProvider {

    private static final String TAG = "WIDGET";

    public static final String REFRESH_WIDGET = "com.oitsme.REFRESH_WIDGET";
    public static final String COLLECTION_VIEW_ACTION = "com.oitsme.COLLECTION_VIEW_ACTION";
    public static final String COLLECTION_VIEW_EXTRA = "com.oitsme.COLLECTION_VIEW_EXTRA";
    private static Handler mHandler = new Handler();
    private Runnable runnable=new Runnable() {
        @Override
        public void run() {
            hideLoading(Utils.getContext());
            Toast.makeText(Utils.getContext(), "Refresh successful", Toast.LENGTH_SHORT).show();
        }
    };

    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager,
                         int[] appWidgetIds) {

        Log.d(TAG, "ListWidgetProvider onUpdate");
        for (int appWidgetId : appWidgetIds) {
            // Get the view corresponding to the AppWidget
            RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.layout_widget);

            // Set the intent that responds to "button(bt_refresh)"
            Intent btIntent = new Intent().setAction(REFRESH_WIDGET);
            PendingIntent btPendingIntent = PendingIntent.getBroadcast(context, 0, btIntent, PendingIntent.FLAG_UPDATE_CURRENT);
            remoteViews.setOnClickPendingIntent(R.id.tv_refresh, btPendingIntent);

            // Set the adapter for "ListView".
            // (01) intent: The intent corresponding to starting ListWidgetService(RemoteViewsService).
            // (02) setRemoteAdapter: Set the adapter of gridview.
            // to associate ListView with ListWidgetService by setRemoteAdapter
            // for the purpose of updating the ListView via ListWidgetService
            Intent serviceIntent = new Intent(context, ListWidgetService.class);
            remoteViews.setRemoteAdapter(R.id.lv_device, serviceIntent);


            // Set the intent template that responds to "ListView"
            // Description: "Collection control (such as GridView, ListView, StackView, etc.)" contains many child elements, such as GridVi
For the above code, let's focus on the onUpdate() method. In onUpdate() we implement two main functions, the first function is to click on events outside the ListView, such as clicking on "Refresh" to update the widget. The second function is to adapt the ListView and implement the click event of the Item control inside the ListView. In this method, we first get an instance of RemoteView, which corresponds to the View of our Widget layout, and the comments are written in detail about the implementation of the click event, so we won't explain too much here. The point is to understand how to implement and adapt the ListView, see the next section for details.
IV.RemoteViewsFactory implementation of list adaptation
We mentioned RemoteViewsFactory above. This class is actually analogous to the Adapter of ListView, which exists to adapt the data of ListView. Only here it is implemented by replacing Adapter with RemoteViews. Take a look at the code in the ListRemoteViewsFactory.
class ListRemoteViewsFactory implements RemoteViewsService.RemoteViewsFactory {
    private final static String TAG="Widget";
    private Context mContext;
    private int mAppWidgetId;

    private static List
 mDevices;

    /**
     * Construct the GridRemoteViewsFactory
     */
    public ListRemoteViewsFactory(Context context, Intent intent) {
        mContext = context;
        mAppWidgetId = intent.getIntExtra(AppWidgetManager.EXTRA_APPWIDGET_ID,
                AppWidgetManager.INVALID_APPWIDGET_ID);
    }

    @Override
    public RemoteViews getViewAt(int position) {
        // HashMap
With RemoteViewsFactory, you also need RemoteViewsService to associate with the ListView. Let's look at the implementation class of RemoteViewsService, ListWidgetService, which is very simple and only overrides the onGetViewFactory method.
public class ListWidgetService extends RemoteViewsService {

    @Override
    public RemoteViewsService.RemoteViewsFactory onGetViewFactory(Intent intent) {
        return new ListRemoteViewsFactory(this, intent);
    }
}

At this point we can go back to the onUpdate() method in the ListWidgetProvider to see how the ListWidgetService is associated with the ListView.
 // Set the adapter for "ListView".
 // (01) intent: The intent corresponding to starting ListWidgetService(RemoteViewsService)
 // (02) setRemoteAdapter: Set the adapter of the ListView
 // to associate ListView with ListWidgetService by setRemoteAdapter
 // for the purpose of updating the ListView via ListWidgetService
  Intent serviceIntent = new Intent(context, ListWidgetService.class);
  remoteViews.setRemoteAdapter(R.id.lv_device, serviceIntent);


V. Click event handling
I'm sure we all know about event clicks in widgets and adapting ListViews. For example, we can't set an event listener to the control to handle it in the dropback method like we can in the app after we clicked refresh in the widget. We mentioned at the beginning of the article that widgets rely on broadcasts, so when we click on a refresh we are actually just sending out a broadcast. If we don't handle the broadcast then the click event is meaningless. So, let's look at the second more important method in ListWidgetProvider, onReceive(). This method is relatively simple, as long as we handle the particular broadcast accordingly.
@Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);
	        if (action.equals(COLLECTION_VIEW_ACTION)) { // handle the events in the list
            // accept the broadcast of the "ListView" click event
            int type = intent.getIntExtra("Type", 0);
            int appWidgetId = intent.getIntExtra(AppWidgetManager.EXTRA_APPWIDGET_ID,
                    AppWidgetManager.INVALID_APPWIDGET_ID);
            int index = intent.getIntExtra(COLLECTION_VIEW_EXTRA, 0);
            switch (type) {
                case 0:
                    Toast.makeText(context, "item" + index, Toast.LENGTH_SHORT).show();
                    break;
                case 1:
                    Toast.makeText(context, "lock" + index, Toast.LENGTH_SHORT).show();
                    break;
                case 2:
                    Toast.makeText(context, "unlock"+index, Toast.LENGTH_SHORT).show();
                    break;
            }
        } else if (action.equals(REFRESH_WIDGET)) {// Handle refresh events
            // accept the broadcast of the "bt_refresh" click event
            Toast.makeText(context, "Refresh... ", Toast.LENGTH_SHORT).show();
            final AppWidgetManager mgr = AppWidgetManager.getInstance(context);
            final ComponentName cn = new ComponentName(context,ListWidgetProvider.class);
            ListRemoteViewsFactory.refresh();
            mgr.notifyAppWidgetViewDataChanged(mgr.getAppWidgetIds(cn),R.id.lv_device);
            mHandler.postDelayed(runnable,2000);
            showLoading(context);
        }
        super.onReceive(context, intent);
    }

Finally, don't forget that ListWidgetProvider is the broadcast and ListWidgetService is the service, both of which we need to register in the AndroidManifest file at
VI. Summary
This completes the explanation of the list widget. I just feel that the logic of the article is a bit messy. If you don't understand it, you can refer to the demo source code below. In fact, the demo of Widget was already written several months ago, but due to the recent tight project and my first contact with Widget control, I didn't start to write this article until recently. So there are mistakes and unreasonable places in the article, welcome to leave comments to correct them.
Reference


 https://developer.android.com/guide/topics/appwidgets/
Source code download
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