Android判断Activity是否在AndroidManifest，移动端应用开发试题

throw new IllegalStateException(“Cannot start assistant activity on a hidden session”);
case ActivityManager.START_CANCELED:
throw new AndroidRuntimeException("Activity could not be started for " + intent);
default:
throw new AndroidRuntimeException("Unknown error code " + res + " when starting " + intent);
}
}

可以看到当结果为

case ActivityManager.START_INTENT_NOT_RESOLVED:

case ActivityManager.START_CLASS_NOT_FOUND:

​就会报 throw new ActivityNotFoundException("Unable to find explicit activity class " + ((Intent) intent).getComponent().toShortString() + “; have you declared this activity in your AndroidManifest.xml?”);

这下我们就知道了如果没在清单文件中添加这个注册，报错的位置。

AMS是如何判断activity没有注册的，首先我们得明白startActivity执行的主流程

这个篇幅太多了，可以自己去源码跟一下，这里不作介绍，

我们这里分析主要流程代码

找到在ASR.startActivity （ActivityStarter）中返回了

START_INTENT_NOT_RESOLVED，START_CLASS_NOT_FOUND

private int startActivity(IApplicationThread caller, Intent intent, Intent ephemeralIntent, String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo, IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid, String callingPackage, int realCallingPid, int realCallingUid, int startFlags, SafeActivityOptions options, boolean ignoreTargetSecurity, boolean componentSpecified, ActivityRecord[] outActivity, TaskRecord inTask, boolean allowPendingRemoteAnimationRegistryLookup) {
int err = ActivityManager.START_SUCCESS;
…
//接下来开始做一些校验判断
if (err == ActivityManager.START_SUCCESS && intent.getComponent() == null) {
// We couldn’t find a class that can handle the given Intent.
// That’s the end of that! err = ActivityManager.START_INTENT_NOT_RESOLVED;
// 从Intent中无法找 到相应的Component
}
if (err == ActivityManager.START_SUCCESS && aInfo == null) {
// We couldn’t find the specific class specified in the Intent.
// Also the end of the line.
err = ActivityManager.START_CLASS_NOT_FOUND;
// 从Intent中无法找到相 应的ActivityInfo
}
…
if (err != START_SUCCESS) {
//不能成功启动了，返回err
if (resultRecord != null) {
resultStack.sendActivityResultLocked(-1, resultRecord, resultWho, requestCode, RESULT_CANCELED, null);
}
SafeActivityOptions.abort(options);
return err;
}
//创建出我们的目标ActivityRecord对象，存到传入数组0索引上
ActivityRecord r = new ActivityRecord(mService, callerApp, callingPid, callingUid, callingPackage, intent, resolvedType, aInfo, mService.getGlobalConfiguration(), resultRecord, resultWho, requestCode, componentSpecified, voiceSession != null, mSupervisor, checkedOptions, sourceRecord);
…
return startActivity(r, sourceRecord, voiceSession, voiceInteractor, startFlags, true /* doResume */, checkedOptions, inTask, outActivity);
}

但是 intent.getComponent()，aInfo又是从哪儿获取的呢，我们回溯到

startActivityMayWait.

看下上面的aInfo哪来的.

ActivityInfo resolveActivity(Intent intent, ResolveInfo rInfo, int startFlags, ProfilerInfo profilerInfo) {
​ final ActivityInfo aInfo = rInfo != null ? rInfo.activityInfo : null;
if (aInfo != null) {
// Store the found target back into the intent, because now that
// we have it we never want to do this again. For example, if the
// user navigates back to this point in the history, we should
// always restart the exact same activity.
intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));
// Don’t debug things in the system process …
}
return aInfo;
}

发现是从rInfo来的

ResolveInfo resolveIntent(Intent intent, String resolvedType, int userId, int flags, int filterCallingUid) {
synchronized (mService) {
​ try {…final long token = Binder.clearCallingIdentity();
try {
return mService.getPackageManagerInternalLocked().resolveIntent(intent, resolvedType, modifiedFlags, userId, true, filterCallingUid);
} finally {
Binder.restoreCallingIdentity(token);
} …
}
}
}

rInfo的获取

PackageManagerInternal getPackageManagerInternalLocked() {
if (mPackageManagerInt == null) {
​ mPackageManagerInt = LocalServices.getService(PackageManagerInternal.class);
}
return mPackageManagerInt;
}

具体实现类是PackageManagerService

​@Override
public ResolveInfo resolveIntent(Intent intent, String resolvedType, int flags, int userId) {
return resolveIntentInternal(intent, resolvedType, flags, userId, false, Binder.getCallingUid());
}

看resolveIntentInternal

private ResolveInfo resolveIntentInternal(Intent intent, String resolvedType,int flags, int userId, boolean resolveForStart, int filterCallingUid) {
try {…
//获取ResolveInfo列表

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