理解RemoteViews

什么是remoteViews？按照字面意思是远程View，但RemoteViews并没有继承View，而是继承Object。它的作用是可以跨进程更新界面，听起来有点神奇。RemoteViews在Android中的使用场景有两种：通知栏和桌面小部件

RemoteViews的应用

1.在通知栏上的应用

①使用系统默认的样式弹出通知

Notification notification= new Notification();

notification.icon = R.drawable.notify;

notification.when = System.currentTimeMillis();

notification.tickerText = "通知";

notification.flags = Notification.FLAG_AUTO_CANCEL;

//创建延时意图

Intent intent = new Intent(this, OtherActivity.class);

PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent,

PendingIntent.FLAG_UPDATE_CURRENT);

notification.setLatestEventInfo(this,"通知", "具体内容", pendingIntent):

NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);

nm.notify(0, notification);

②使用RemoteViews可以自定义布局，通过RemoteViews来加载布局文件即可改变通知的样式，具体代码如下

Notification notification= new Notification();

notification.icon = R.drawable.notify;

notification.when = System.currentTimeMillis();

notification.tickerText = "通知";

notification.flags = Notification.FLAG_AUTO_CANCEL;

//创建延时意图

Intent intent = new Intent(this, OtherActivity.class);

PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent,

PendingIntent.FLAG_UPDATE_CURRENT);

RemoteViews remoteViews = new RemoteViews(getPackageName(), R.layout.layout_notification);

remoteViews.setTextViewText(R.id.msg, "自定义通知");

remoteViews.setImageViewResource(R.id.icon, R.drawable.icon);

PendingIntent pendingIntent2 = PendingIntent.getActivity(this, 0,

new Intent(this, SecondActivity.class), PendingIntent.FLAG_UPDATE_CURRENT);

remoteViews.setOnClickPendingIntent(R.id.btn, pendingIntent2);

notification.contentView = remoteViews;

notification.contentIntent = pendingIntent;

NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);

nm.notify(1, notification);

2.在桌面小部件上的应用

AppWidgetProvider是Android中提供的用于实现桌面小部件的类，实际上是一个广播。具体实现步骤如下

①定义小部件界面

自定义xml布局文件，具体布局样式根据实际开发需要，如widget.xml

②定义小部件配置信息

在res/xml下新建appwidget_provider_info.xml，名称任意

android:initialLayout="@layout/widget"

android:minHeght="84dp"

android:minWidth="84dp"

android:updatePeriodMillis="86400000" >

③定义小部件的实现类

public class MyAppWidgetProvider extends AppWidgetProvider {

private static final String CLICK_ACTION = "com.hj.action.click";

@Override

public void onReceive(final Context context, Intent intent) {

super.onReceive(context, intent);

if (intent.getAction().equals(CLICK_ACTION)) {

new Thread(new Runnable() {

@Override

public void run() {

Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(),

R.drawable.ic_launcher_v2);

AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);

for (int i = 0; i < 10; i++) {

float degree = (i * 10) % 360;

RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.widget);

remoteViews.setImageViewBitmap(R.id.container, rotateBitmap(context, bitmap, degree));

Intent intent1 = new Intent(CLICK_ACTION);

PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, intent1, 0);

remoteViews.setOnClickPendingIntent(R.id.container, pendingIntent);

appWidgetManager.updateAppWidget(new ComponentName(context, MyAppWidgetProvider.class), remoteViews);

SystemClock.sleep(30);

}

}

}).start();

}

}

@Override

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

super.onUpdate(context, appWidgetManager, appWidgetIds);

int count = appWidgetIds.length; for (int i = 0; i < count; i++) {

int appWidgetId = appWidgetIds[i];

onWidgetUpdate(context, appWidgetManager, appWidgetId);

}

}

private void onWidgetUpdate(Context context, AppWidgetManager appWidgetManager, int appWidgetId) {

RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.widget);

Intent intent = new Intent();

intent.setAction(CLICK_ACTION);

PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, intent, 0);

remoteViews.setOnClickPendingIntent(R.id.container, pendingIntent);

appWidgetManager.updateAppWidget(appWidgetId, remoteViews);

}

private Bitmap rotateBitmap(Context context, Bitmap bitmap, float degree) {

Matrix matrix = new Matrix();

matrix.reset();

matrix.setRotate(degree);

Bitmap tmpBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(),

bitmap.getHeight(), matrix, true);

return tmpBitmap;

}

}

④在AndroidManifest.xml声明小部件

桌面部件实际上是一个广播组件，必须要注册。APPWIDGET_UPDATE代表该广播是作为小部件的标识存在的

android:name=".MyAppWidgetProvider>

android:name="android.appwidget.provider"

android:resource="@xml/appwidget_provider_info">

PendingIntent

PendingIntent表示一种处于pending状态的意图，而pending状态表示的是一种待定、等待、即将发生的意思。PendingIntent支持三种待定意图：启动Activity、启动Service和发送广播。

1.PendingIntent的Flag介绍

FLAG_ONE_SHOT

PendingIntent只能被使用一次，然后会自动cancel；如果后续还有相同的PendingIntent，那么他们的send方法就会调用失败

FLAG_NO_CREATE

PendingIntent不会主动创建，如果当前PendingIntent不存在，那么三种意图方法调用会直接返回null，获取PendingIntent会失败，它无法单独使用

FLAG_CANCEL_CURRENT

PendingIntent如果已经存在，那么它们都会被cancle，然后系统会创建一个新的PendingIntent。对于通知栏而言，那些被cancel的消息单击后无法打开

FLAG_UPDATE_CURRENT

PendingIntent如果已经存在，那么它们都会被更新

通知栏而言，notify(int, notification)方法中，若id值每次都不同的话，需要考虑到flag参数对应消息接收的情况

RemoteViews内部机制

RemoteViews目前并不能支持所有的View的类型，不能支持自定义View、EditText等，同时没有提供findViewById方法，无法直接访问View元素。RemoteViews会通过Binder传递到SystemServer进程，系统会通过RemoteViews中包名等信息去得到该应用的资源并加载布局文件，当需要更新RemoteViews时，我们需要通过一系列set方法并通过NotificationManager和AppWidgetManager来提交更新任务，具体的更新操作也是在SystemServer进程中完成的。RemoteViews提供一个Action的概念，Action代表一个View操作，系统首先将View操作封装到Action对象并跨进程传输到远程进程，接着在远程进程中执行Action对象中的具体操作