[转] Android中的AppWidget(下) by李先静

最新推荐文章于 2023-10-10 16:38:03 发布

原创最新推荐文章于 2023-10-10 16:38:03 发布 · 808 阅读

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#android #exception #null #resources #layout #class

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本文深入解析了Android系统中AppWidget的工作原理，重点介绍了AppWidgetHost的功能及其如何通过监听事件和创建AppWidgetHostView来更新Widget。同时，还探讨了Launcher作为Host的实现方式以及AppWidgetService在解除AppWidgetProvider与Host之间耦合方面的作用。

文章出处：http://www.limodev.cn/blog
作者联系方式：李先静 <xianjimli at hotmail dot com>

(续)

AppWidgetHost

AppWidgetHost是真正容纳AppWidget的地方，它的主要功能有两个：

o 监听来自AppWidgetService的事件：

    class Callbacks extends IAppWidgetHost.Stub {
        public void updateAppWidget(int appWidgetId, RemoteViews views) {
            Message msg = mHandler.obtainMessage(HANDLE_UPDATE);
            msg.arg1 = appWidgetId;
            msg.obj = views;
            msg.sendToTarget();
        }
 
        public void providerChanged(int appWidgetId, AppWidgetProviderInfo info) {
            Message msg = mHandler.obtainMessage(HANDLE_PROVIDER_CHANGED);
            msg.arg1 = appWidgetId;
            msg.obj = info;
            msg.sendToTarget();
        }
    }

这是主要处理update和provider_changed两个事件,根据这两个事件更新widget。

    class UpdateHandler extends Handler {
        public UpdateHandler(Looper looper) {
            super(looper);
        }
 
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case HANDLE_UPDATE: {
                    updateAppWidgetView(msg.arg1, (RemoteViews)msg.obj);
                    break;
                }
                case HANDLE_PROVIDER_CHANGED: {
                    onProviderChanged(msg.arg1, (AppWidgetProviderInfo)msg.obj);
                    break;
                }
            }
        }
    }

o 另外一个功能就是创建AppWidgetHostView。前面我们说过RemoteViews不是真正的View，只是View的描述，而AppWidgetHostView才是真正的View。这里先创建AppWidgetHostView，然后通过AppWidgetService查询appWidgetId对应的RemoteViews，最后把RemoteViews传递给AppWidgetHostView去updateAppWidget。

    public final AppWidgetHostView createView(Context context, int appWidgetId,
            AppWidgetProviderInfo appWidget) {
        AppWidgetHostView view = onCreateView(context, appWidgetId, appWidget);
        view.setAppWidget(appWidgetId, appWidget);
        synchronized (mViews) {
            mViews.put(appWidgetId, view);
        }
        RemoteViews views = null;
        try {
            views = sService.getAppWidgetViews(appWidgetId);
        } catch (RemoteException e) {
            throw new RuntimeException("system server dead?", e);
        }
        view.updateAppWidget(views);
        return view;
    }

AppWidgetHostView

AppWidgetHostView是真正的View，但它只是一个容器，用来容纳实际的AppWidget的View。这个AppWidget的View是根据RemoteViews的描述来创建。这是在updateAppWidget里做的：

public void updateAppWidget(RemoteViews remoteViews) {
...
            if (content == null && layoutId == mLayoutId) {
                try {
                    remoteViews.reapply(mContext, mView);
                    content = mView;
                    recycled = true;
                    if (LOGD) Log.d(TAG, "was able to recycled existing layout");
                } catch (RuntimeException e) {
                    exception = e;
                }
            }
 
            // Try normal RemoteView inflation
            if (content == null) {
                try {
                    content = remoteViews.apply(mContext, this);
                    if (LOGD) Log.d(TAG, "had to inflate new layout");
                } catch (RuntimeException e) {
                    exception = e;
                }
            }
...
        if (!recycled) {
            prepareView(content);
            addView(content);
        }
 
        if (mView != content) {
            removeView(mView);
            mView = content;
        }
...
}

remoteViews.apply创建了实际的View，下面代码可以看出:

    public View apply(Context context, ViewGroup parent) {
        View result = null;
 
        Context c = prepareContext(context);
 
        Resources r = c.getResources();
        LayoutInflater inflater = (LayoutInflater) c
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
 
        inflater = inflater.cloneInContext(c);
        inflater.setFilter(this);
 
        result = inflater.inflate(mLayoutId, parent, false);
 
        performApply(result);
 
        return result;
    }

Host的实现者

AppWidgetHost和AppWidgetHostView是在框架中定义的两个基类。应用程序可以利用这两个类来实现自己的Host。Launcher是缺省的桌面，它是一个Host的实现者。

LauncherAppWidgetHostView扩展了AppWidgetHostView，实现了对长按事件的处理。

LauncherAppWidgetHost扩展了AppWidgetHost，这里只是重载了onCreateView，创建LauncherAppWidgetHostView的实例。

AppWidgetService

AppWidgetService存在的目的主要是解开AppWidgetProvider和AppWidgetHost之间的耦合。如果AppWidgetProvider和AppWidgetHost的关系固定死了，AppWidget就无法在任意进程里显示了。而有了AppWidgetService，AppWidgetProvider根本不需要知道自己的AppWidget在哪里显示了。