Intents and Intent Filters

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Intents 分为显示Intents和隐士intents

1：显示的Intents举例如下：一般用于启动特定的app 组件，如下例就是启动downloaderservice。

Intent downloadIntent = new Intent(this, DownloadService.class);
downloadIntent.setData(Uri.parse(fileUrl));
startService(downloadIntent);

2：隐士的Intents不指定类名，而是指定满足某种条件就可以，当然符合条件的activity或者service 可能有好几个，这个时候系统就会弹出一个对话框，让用户自己选择。

Intent sendIntent = new Intent();
sendIntent.setAction(Intent.ACTION_SEND);
sendIntent.putExtra(Intent.EXTRA_TEXT, textMessage);
sendIntent.setType("text/plain");

这样当所有在manifest中定义ACTION_SEND 的activity 或者service 都会响应这个Intent。但是如果没有一个activit或者service响应，你的app可能就要crash掉，所以我们一般先查询是否有activity 响应这个Intent，如果有响应，在发送，就像下面这样.

// Create the text message with a string
Intent sendIntent = new Intent();
sendIntent.setAction(Intent.ACTION_SEND);
sendIntent.putExtra(Intent.EXTRA_TEXT, textMessage);
sendIntent.setType("text/plain");

// Verify that the intent will resolve to an activity
if (sendIntent.resolveActivity(getPackageManager()) != null) {
startActivity(sendIntent);
}

其中intent.resolveactivity 会调用pm.resolveactiviy 开查询是否有符合的activity.

/frameworks/base/core/java/android/content/Intent.java
5790 public ComponentName resolveActivity(PackageManager pm) {
5791 if (mComponent != null) {
5792 return mComponent;
5793 }
5794
5795 ResolveInfo info = pm.resolveActivity(
5796 this, PackageManager.MATCH_DEFAULT_ONLY);
5797 if (info != null) {
5798 return new ComponentName(
5799 info.activityInfo.applicationInfo.packageName,
5800 info.activityInfo.name);
5801 }
5802
5803 return null;
5804 }

而activity的信息是在安装的时候由PMS parse 出来。后面在详细分析.

如果有多个activity响应的话，可以弹出一个对话框让用户选择，sample code 如下：

Intent sendIntent = new Intent(Intent.ACTION_SEND);
// 选择Android 默认的chooser，也可以客制化
String title = getResources().getString(R.string.chooser_title);
// Create intent to show the chooser dialog
Intent chooser = Intent.createChooser(sendIntent, title);
// Verify the original intent will resolve to at least one activity
if (sendIntent.resolveActivity(getPackageManager()) != null) {
startActivity(chooser);
}

resolveactivity 最终在ActivityStackSupervisor.java实现。重点是869行会向packagemanager 查询是否有符合的intent

/frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java
ActivityInfo resolveActivity(Intent intent, String resolvedType, int startFlags,
864 ProfilerInfo profilerInfo, int userId) {
865 // Collect information about the target of the Intent.
866 ActivityInfo aInfo;
867 try {
868 ResolveInfo rInfo =
869 AppGlobals.getPackageManager().resolveIntent(
870 intent, resolvedType,
871 PackageManager.MATCH_DEFAULT_ONLY
872 | ActivityManagerService.STOCK_PM_FLAGS, userId);
873 aInfo = rInfo != null ? rInfo.activityInfo : null;
874 } catch (RemoteException e) {
875 aInfo = null;
876 }
877
878 if (aInfo != null) {
879 // Store the found target back into the intent, because now that
880 // we have it we never want to do this again. For example, if the
881 // user navigates back to this point in the history, we should
882 // always restart the exact same activity.
883 intent.setComponent(new ComponentName(
884 aInfo.applicationInfo.packageName, aInfo.name));
885
886 // Don't debug things in the system process
887 if ((startFlags&ActivityManager.START_FLAG_DEBUG) != 0) {
888 if (!aInfo.processName.equals("system")) {
889 mService.setDebugApp(aInfo.processName, true, false);
890 }
891 }
892
893 if ((startFlags&ActivityManager.START_FLAG_OPENGL_TRACES) != 0) {
894 if (!aInfo.processName.equals("system")) {
895 mService.setOpenGlTraceApp(aInfo.applicationInfo, aInfo.processName);
896 }
897 }
898
899 if (profilerInfo != null) {
900 if (!aInfo.processName.equals("system")) {
901 mService.setProfileApp(aInfo.applicationInfo, aInfo.processName, profilerInfo);
902 }
903 }
904 }
905 return aInfo;
906 }

intent filters 有两种方式注册，一种是在manifest文件中静态注册如下所示：只要action是send的intend 都会被myactivity 接收到.

</intent-filter>
</activity>

第二种方式是在java code中动态注册.

546 final IntentFilter filter = new IntentFilter();
547
548 filter.addAction(Intent.ACTION_TIME_TICK);
549 filter.addAction(Intent.ACTION_TIME_CHANGED);
550 filter.addAction(Intent.ACTION_TIMEZONE_CHANGED);

552 getContext().registerReceiver(mIntentReceiver, filter, null, getHandler());

注册三个action.

有两个action 需要额外主要：

ACTION_MAIN：这个是aplication的入口activity，不接收任何intent data。

CATEGOTY_LAUNCHER : 这个会把activity的icon放到桌面（launch）。
这两个必须按顺序放好，才能让activity在桌面上显示图标
pending intent:

pending intent 是intent的一个包装，其设计的目的是让其他process的application 有权限启动其他process的activity,service,broadcast,就像在自己process 一样.

主要由三种用途：

notification，alarmManager或者app wiget 的时候可以可以传递一个pending intent，这样当用户点击的时候其他一个activity,service,broadcast.

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