Android 关于RemoteViews的理解（二）

前言

上一篇文章《Android 关于RemoteViews的理解（一）》介绍了RemoteViews的使用场景，我们学习东西的时候要知其然知其所以然。我之前考虑一篇文章就可以说明RemoteViews的内部机制了，但是当我仔细查阅资料学习之后发现要说透这个可能会需要几篇文章，所以关于RemoteViews的内部机制会拆分成几篇文章，这里是第一篇

1:构造方法及支持的View类型

在正式了解RemoteViews内部机制前我们有必要了解下RemoteViews支持的View类型，创建RomoteViews最常用的方法是：

 val remoteViews = RemoteViews(packageName, R.layout.xxx)

这个构造方法的源码如下：

/*** Create a new RemoteViews object that will display the views contained* in the specified layout file.** @param packageName Name of the package that contains the layout resource* @param layoutId The id of the layout resource*/public RemoteViews(String packageName, int layoutId) {this(getApplicationInfo(packageName, UserHandle.myUserId()), layoutId);}

其中packageName是当前应用的包名，layoutId是需要加载的布局文件。既然RemoteViews其中一个应用场景是在通知栏，这就限定了某些View它是不支持的，比如在通知栏里使用Edittext，这个应用场景是无法想象的，下面为谷歌官方开发文档中列出的RemoteViews支持的所有类型：

layouts

AdapterViewFlipper
FrameLayout
GridLayout
GridView
LinearLayout
ListView
RelativeLayout
StackView
ViewFlipper

widgets

AnalogClock
Button
Chronometer
ImageButton
ImageView
ProgressBar
TextClock
TextView

值得注意的是RemoteViews只支持上述View类型而且不支持他们的子类，以及其他自定义View，我知道到这里肯定有人会去验证一波，所以我就直接帮你们验证了，当我在自定义的通知栏中使用了CheckBox，通知栏没有弹出，查看Logcat可以看到：

2020-12-22 21:54:24.752 1170-1283/? E/Netd: getNetworkForDns: getNetId from enterpriseCtrl is netid 0
2020-12-22 21:54:24.931 2199-2199/? E/StatusBar: couldn't inflate view for notification com.sjr.remoteviewsdemo/0x1android.view.InflateException: Binary XML file line #12 in com.sjr.remoteviewsdemo:layout/view_notification: Binary XML file line #12 in com.sjr.remoteviewsdemo:layout/view_notification: Error inflating class android.widget.CheckBoxCaused by: android.view.InflateException: Binary XML file line #12 in com.sjr.remoteviewsdemo:layout/view_notification: Error inflating class android.widget.CheckBoxCaused by: android.view.InflateException: Binary XML file line #12 in com.sjr.remoteviewsdemo:layout/view_notification: Class not allowed to be inflated android.widget.CheckBox

上面的异常信息表明CheckBox不能在RemoteViews中使用。当然其他的自定义View想要验证的可以自己走一下，异常跟上面的一致，只是控件名称换了而已。

2：RemoteViews内部机制

RemoteViews是在远程进程中显示，所以不能直接使用findViewById，也就无法访问直接访问View里面的元素，二十通过RemoteViews提供的一系列set方法来完成，官方文档提供的set方法如下：

void setFloat(int viewId, String methodName, float value)
Call a method taking one float on a view in the layout for this RemoteViews.void    setIcon(int viewId, String methodName, Icon value)
Call a method taking one Icon on a view in the layout for this RemoteViews.void setImageViewBitmap(int viewId, Bitmap bitmap)
Equivalent to calling ImageView#setImageBitmap(Bitmap)void  setImageViewIcon(int viewId, Icon icon)
Equivalent to calling ImageView#setImageIcon(Icon)void  setImageViewResource(int viewId, int srcId)
Equivalent to calling ImageView#setImageResource(int)void   setImageViewUri(int viewId, Uri uri)
Equivalent to calling ImageView#setImageURI(Uri)void    setInt(int viewId, String methodName, int value)
Call a method taking one int on a view in the layout for this RemoteViews.void  setLabelFor(int viewId, int labeledId)
Equivalent to calling View#setLabelFor(int).void    setLightBackgroundLayoutId(int layoutId)
Provides an alternate layout ID, which can be used to inflate this view.void    setLong(int viewId, String methodName, long value)
Call a method taking one long on a view in the layout for this RemoteViews.void setOnClickFillInIntent(int viewId, Intent fillInIntent)
When using collections (eg.void setOnClickPendingIntent(int viewId, PendingIntent pendingIntent)
Equivalent to calling View.setOnClickListener(android.view.View.OnClickListener) to launch the provided PendingIntent.void  setOnClickResponse(int viewId, RemoteViews.RemoteResponse response)
Equivalent of calling View.setOnClickListener(android.view.View.OnClickListener) to launch the provided RemoteResponse.void setPendingIntentTemplate(int viewId, PendingIntent pendingIntentTemplate)
When using collections (eg.void setProgressBar(int viewId, int max, int progress, boolean indeterminate)
Equivalent to calling ProgressBar#setMax, ProgressBar#setProgress, and ProgressBar#setIndeterminate If indeterminate is true, then the values for max and progress are ignored.void setRelativeScrollPosition(int viewId, int offset)
Equivalent to calling ListView#smoothScrollByOffset(int).void   setRemoteAdapter(int appWidgetId, int viewId, Intent intent)
This method was deprecated in API level 15. This method has been deprecated. See setRemoteAdapter(int, Intent)void  setRemoteAdapter(int viewId, Intent intent)
Equivalent to calling AbsListView.setRemoteViewsAdapter(Intent).void    setScrollPosition(int viewId, int position)
Equivalent to calling ListView#smoothScrollToPosition(int).void setShort(int viewId, String methodName, short value)
Call a method taking one short on a view in the layout for this RemoteViews.void    setString(int viewId, String methodName, String value)
Call a method taking one String on a view in the layout for this RemoteViews.void   setTextColor(int viewId, int color)
Equivalent to calling TextView.setTextColor(int).void   setTextViewCompoundDrawables(int viewId, int left, int top, int right, int bottom)
Equivalent to calling TextView#setCompoundDrawablesWithIntrinsicBounds(int, int, int, int).void setTextViewCompoundDrawablesRelative(int viewId, int start, int top, int end, int bottom)
Equivalent to calling TextView#setCompoundDrawablesRelativeWithIntrinsicBounds(int, int, int, int).void setTextViewText(int viewId, CharSequence text)
Equivalent to calling TextView#setText(CharSequence)void    setTextViewTextSize(int viewId, int units, float size)
Equivalent to calling TextView#setTextSize(int, float)

上面很多set方法是通过反射来完成的。通过这些set方法可以对RemoteViews进行相关的操作：如：

void setTextViewText(int viewId, CharSequence text)
Equivalent to calling TextView#setText(CharSequence)void    setTextColor(int viewId, int color)
Equivalent to calling TextView.setTextColor(int).

用来设置TextView的文本和字体颜色。

RemoteViews主要用于通知栏和桌面小部件，所以分析他们的工作过程可以更具象化的了解RemoteViews的内部机制。通知栏和桌面小部件分别由NotificationManager和AppWidgetManager管理，它们通过Binder和系统服务进程中的NotificationManagerService和AppWidgetSetvice进行通信，通过这个可以看出来其实通知栏和桌面小部件的布局文件其实是在系统Service中加载并且运行在系统服务（SystemServer）中，这样我们应用中的进程就和系统进程组成了一个跨进程通信的场景了（关于跨进程通信有兴趣的小伙伴可以查看我之前写的两篇文章）
《Android 关于IPC机制的理解(一)》

《Android 关于IPC机制的理解(二)》

回到主题，查看源码我们发现RemoteViews实现了Parcelable接口，所以RemoteViews可以进行跨进程传输，而系统会通过构造RemoteViews时传递的包名去得到这个包名应用的资源文件，再通过LayoutInflater去加载构造时一起传递的布局文件。这个时候通过之前介绍的set方法提交的操作请求对view进行更新和操作。当RemoteViews加载完成之后RemoteViews就可以在SystemServer中显示。如果通知栏和小部件需要更新，就需要重新调用set方法，通过NotificationManager和AppWidgetManager来向SystemServer的相关Service提交更新任务了。

小结

这篇文章对RemoteViews的创建和工作流程进行了粗略说明，下一篇文章会从源码的角度对相关的内部机制流程进行分析。