View - RemoteViews

设计Android的工程师起名字还是挺规范的，而且一眼就知道是什么意思。RemoteViews，顾名思义，远程的View。Android为了能让进程A显示进程B的View，设计了这么一种View（其实不是真正的View）。其实我们开发过程中，发通知到状态栏显示也是利用了RemoteViews，我们来了解一下RemoteViews吧。

我们先看看RemoteViews怎么配合Notification使用：

import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.widget.RemoteViews;

@SuppressLint("NewApi")
public class MainActivity extends Activity {

    private RemoteViews contentView;
    private Notification notification;
    private NotificationManager notificationManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        sendNotification();
    }

    private void sendNotification() {
        contentView = new RemoteViews(getPackageName(), R.layout.layout_remote);
        contentView.setTextViewText(R.id.remote_title, "Remote View Title");
        contentView.setTextViewText(R.id.remote_content, "This Remote View Content ... \nThis Remote View Content ... \nThis Remote View Content ...");
        Intent intent = new Intent(this, MainActivity.class);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
        // RemoteViews的事件只能是PendingIntent
        contentView.setOnClickPendingIntent(R.id.remote_content, pendingIntent);
        notification = new Notification.Builder(this)
                .setWhen(System.currentTimeMillis())    // 设置显示通知的时间
                .setAutoCancel(true)                    // 设置是否可以手动取消
                .setSmallIcon(R.mipmap.ic_launcher)     // 设置在状态栏的小图标，如果没有设置，不显示通知
                .setCustomBigContentView(contentView)   // 设置自定义View，setCustomBigContentView可以显示remoteviews的完整高度，setCustomContentView只能显示系统通知栏高度。
                .build();
        notificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        // 发通知
        notificationManager.notify(1, notification);
    }

}

其中R.layout.layout_remote布局文件如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="10dp"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/remote_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="18sp"
        android:textColor="@android:color/holo_blue_light"
        />

    <TextView
        android:id="@+id/remote_content"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="3dp"
        android:textSize="16sp"
        android:textColor="@android:color/darker_gray"
        />

</LinearLayout>

效果如图所示：

因为我是调用setCustomBigContentView来加载RemoteViews的，所以RemoteViews可以显示完整，不受系统通知栏高度限制。

我们接下来解析状态栏是怎么加载我们定义的RemoteViews的，Let’s Go !!

RemoteViews加载

我们首先要知道状态栏是SystemServer进程，而我们定义的RemoteViews是在我们App进程，状态栏要加载并显示我们的RemoteViews，这肯定是通过IPC，主要实现是Binder。

RemoteViews会通过Binder传递给SystemServer进程，系统会根据RemoteViews的包名和布局id等信息，获取到应用的资源（布局文件，图标等），然后通过LayoutInflater加载RemoteViews中的布局文件，最后在状态栏和通知栏显示出来。

RemoteViews更新

RemoteViews提供了很多个方法，更新RemoteViews的布局文件：

// 部分方法
- setTextViewText(viewId, text)                     设置文本
- setTextColor(viewId, color)                       设置文本颜色
- setTextViewTextSize(viewId, units, size)          设置文本大小
- setImageViewBitmap(viewId, bitmap)                设置图片
- setImageViewResource(viewId, srcId)               根据图片资源设置图片
- setViewPadding(viewId, left, top, right, bottom)  设置Padding间距
- setOnClickPendingIntent(viewId, pendingIntent)    设置点击事件
- setInt(viewId, methodName, value)                 反射调用参数为int的methodName方法
- setLong(viewId, methodName, value)                反射调用参数为long的methodName方法
...

当调用以上方法来更新RemoteViews时，RemoteViews并 不会立刻更新，只是封装了一系列的Action，然后等待时机更新。

我们从源码分析，当我们调用setTextViewText来更新内容时：

private void updateNotification() {
    contentView.setTextViewText(R.id.remote_content, "This Remote View Update Content ... \nThis Remote View Update Content ... \nThis Remote View Update Content ...");
    notificationManager.notify(1, notification);
}

我们来看看setTextViewText源码：

// RemoteViews类
public void setTextViewText(int viewId, CharSequence text) {
    setCharSequence(viewId, "setText", text);
}

调用了setCharSequence方法：

// RemoteViews类
public void setCharSequence(int viewId, String methodName, CharSequence value) {
    addAction(new ReflectionAction(viewId, methodName, ReflectionAction.CHAR_SEQUENCE, value));
}

addAction方法：

// RemoteViews类
private void addAction(Action a) {
    if (hasLandscapeAndPortraitLayouts()) {
                throw new RuntimeException("RemoteViews specifying separate landscape and portrait" +
                        " layouts cannot be modified. Instead, fully configure the landscape and" +
                        " portrait layouts individually before constructing the combined layout.");
            }
    if (mActions == null) {
        mActions = new ArrayList<Action>();
    }
    mActions.add(a);
    a.updateMemoryUsageEstimate(mMemoryUsageCounter);
}

可以看出，整个set过程，只是封装了一个Action并添加到mActions（一个List）中，所以这个过程并没有更新RemoteViews哦。我们看看ReflectionAction是什么：

// ReflectionAction类
private final class ReflectionAction extends Action {
    ...
    ReflectionAction(int viewId, String methodName, int type, Object value) {
         this.viewId = viewId;
         this.methodName = methodName;
         this.type = type;
         this.value = value;
    }
    ...
}     

就是储存了一些属性，主要是传递给SystemServer进程的一些更新RemoteViews布局信息。

当我们调用notificationManager.notify(1, notification)方法，RemoteViews布局才会开始更新。 
我们来看看notify代码：

// NotificationManager类
public void notify(int id, Notification notification){
    notify(null, id, notification);
}
public void notify(String tag, int id, Notification notification){
    notifyAsUser(tag, id, notification, new UserHandle(UserHandle.myUserId()));
}

最终调用了notifyAsUser方法：

// NotificationManager类
public void notifyAsUser(String tag, int id, Notification notification, UserHandle user){
    ...
    INotificationManager service = getService();
    ...
    final Notification copy = Builder.maybeCloneStrippedForDelivery(notification);
    try {
        service.enqueueNotificationWithTag(pkg, mContext.getOpPackageName(), tag, id,
                copy, idOut, user.getIdentifier());
        ...
    } catch (RemoteException e) {
        throw e.rethrowFromSystemServer();
    }
}

service为INotificationManager的代理对象，调用了enqueueNotificationWithTag方法后，通过Binder，也就调用了NotificationManagerService（INotificationManager的存根对象，存在于SystemServer进程）的enqueueNotificationWithTag方法：

// NotificationManagerService类
public void enqueueNotificationWithTag(String pkg, String packageName, String tag, int id, Notification notification, int[] idOut, @UserIdInt userIdInt) {
    ...
    StatusBarNotification n = new StatusBarNotification(pkg, id, tag, r.uid, r.initialPid, notification);
    try {
        mStatusBar.updateNotification(r.statusBarKey, n)
        ...
    }
    ...
}

调用了StatusBarNotification的updateNotification方法：

// StatusBarNotification类
public void updateNotification(IBinder key, StatusBarNotification notification) {
    ...
     final RemoteViews contentView = notification.notification.contentView;
    ...
    contentView.reapply(mContext, oldEntry.content);
    ...
}

最终在SystemServer进程调用了RemoteViews的reapply方法：

// RemoteViews类
public void reapply(Context context, View v) {
    reapply(context, v, null);
}
public void reapply(Context context, View v, OnClickHandler handler) {
    RemoteViews rvToApply = getRemoteViewsToApply(context);
    if (hasLandscapeAndPortraitLayouts()) {
        if (v.getId() != rvToApply.getLayoutId()) {
            throw new RuntimeException("Attempting to re-apply RemoteViews to a view that" +
                    " that does not share the same root layout id.");
        }
    }
    rvToApply.performApply(v, (ViewGroup) v.getParent(), handler);
}

最终调用了RemoteViews的performApply方法：

// RemoteViews类
private void performApply(View v, ViewGroup parent, OnClickHandler handler) {
    if (mActions != null) {
        handler = handler == null ? DEFAULT_ON_CLICK_HANDLER : handler;
        final int count = mActions.size();
        for (int i = 0; i < count; i++) {
            Action a = mActions.get(i);
            a.apply(v, parent, handler);
        }
    }
}

我们之前setXXX方法时不是储存了Action吗，通过调用performApply方法，遍历所有Action，然后更新RemoteViews的布局文件。代码中，调用了Action的apply方法实现View的更新，Action是一个抽象类，apply方法由子类实现。我们看看ReflectionAction类的apply方法：

// ReflectionAction类
private final class ReflectionAction extends Action {
    ...
    @Override
    public void apply(View root, ViewGroup rootParent, OnClickHandler handler) {
        final View view = root.findViewById(viewId);
        if (view == null) return;
        Class<?> param = getParameterType();
        if (param == null) {
            throws new ActionException("bad type : " + this.type);
        }
        try {
            getMethod(view, this.methodName, param).invoke(view, wrapArg(this.value));
        } catch (ActionException e) {
            throws e;
        } catch (Exception ex) {
            throws new ActionException(ex);
        }
    }
    ...
}     

主要是通过反射，调用View的方法，更新View。

注意

RemoteViews设置的布局文件并不支持所有的View，以下是RemoteViews所支持的View：

layout

FrameLayout，LinearLayout，RelativeLayout，GridLayout

view

Button，ImageView，ImageButton，TextView，ProgressBar，ListView，GridView，StackView，ViewStub，AdapterViewFlipper，ViewFlipper，AnalogClock，Chronometer

小结

通过对RemoteViews的了解，我们灵活的设计出多样式的RemoteViews，还可以在不用应用（A）显示自己应用（B）想要显示的View，这个有需要再探索。

转: https://blog.csdn.net/johanman/article/details/76019771