安卓App启动——Application的启动流程，从startActivity讲起

原创已于 2023-06-07 19:14:47 修改 · 1.6k 阅读

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#安卓 #android #framework #安卓源码

于 2021-11-26 18:30:33 首次发布

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public class ActivityManagerService extends IActivityManager.Stub    implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback, ActivityManagerGlobalLock{
        public int startActivity(IApplicationThread caller, String callingPackage,
              Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
              int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
          return mActivityTaskManager.startActivity(caller, callingPackage, null, intent,
                  resolvedType, resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions);
      }
}

我们可以看到调用了 mActivityTaskManager.startActivity，参数中IApplicationThread 我们留到后面讲。我们先往下追踪

ActivityTaskManagerService.java{

return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
                  resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions,
                  UserHandle.getCallingUserId());

}

UserHandle.getCallingUserId()是获取当前的调用userId我们留到后面讲，当前我们继续追踪。

public int startActivityAsUser(IApplicationThread caller, String callingPackage,
              String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,
              String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,
              Bundle bOptions, int userId) {
          return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
                  resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions, userId,
                  true /*validateIncomingUser*/);//最后一个参数设置了固定值true
      }

private int startActivityAsUser(IApplicationThread caller, String callingPackage,
1179              @Nullable String callingFeatureId, Intent intent, String resolvedType,
1180              IBinder resultTo, String resultWho, int requestCode, int startFlags,
1181              ProfilerInfo profilerInfo, Bundle bOptions, int userId, boolean validateIncomingUser) {
1182          assertPackageMatchesCallingUid(callingPackage);//判断当前调用packagename和调 
                                                             //用uid是否匹配。留后面讲，这 
                                                             //里不细究
1183          enforceNotIsolatedCaller("startActivityAsUser");//判断当前调用userid是否在合 
                                                              //理沙箱合理范围内
1184          //验证用户userid/callingpid/callinguid
1185          userId = getActivityStartController().checkTargetUser(userId, validateIncomingUser,
1186                  Binder.getCallingPid(), Binder.getCallingUid(), "startActivityAsUser");
1187  
1188          // 利用ActivityStarter工厂模式创建ActivityStarter
1189          return getActivityStartController().obtainStarter(intent, "startActivityAsUser")
1190                  .setCaller(caller)
1191                  .setCallingPackage(callingPackage)
1192                  .setCallingFeatureId(callingFeatureId)
1193                  .setResolvedType(resolvedType)
1194                  .setResultTo(resultTo)
1195                  .setResultWho(resultWho)
1196                  .setRequestCode(requestCode)
1197                  .setStartFlags(startFlags)
1198                  .setProfilerInfo(profilerInfo)
1199                  .setActivityOptions(bOptions)
1200                  .setUserId(userId)
1201                  .execute();//执行execute
1202  
1203      }

我们看看execute都执行了什么

int execute() {
        try {
            if (mRequest.intent != null && mRequest.intent.hasFileDescriptors()) {
                throw new IllegalArgumentException("File descriptors passed in Intent");
            }
            final LaunchingState launchingState;
            synchronized (mService.mGlobalLock) {
                final ActivityRecord caller = ActivityRecord.forTokenLocked(mRequest.resultTo);
                final int callingUid = mRequest.realCallingUid == Request.DEFAULT_REAL_CALLING_UID
                        ?  Binder.getCallingUid() : mRequest.realCallingUid;
                launchingState = mSupervisor.getActivityMetricsLogger().notifyActivityLaunching(
                        mRequest.intent, caller, callingUid);
            }
            if (mRequest.activityInfo == null) {
                mRequest.resolveActivity(mSupervisor);
            }
            if (mRequest.intent != null) {
                String intentAction = mRequest.intent.getAction();
                String callingPackage = mRequest.callingPackage;
                if (intentAction != null && callingPackage != null
                        && (Intent.ACTION_REQUEST_SHUTDOWN.equals(intentAction)
                                || Intent.ACTION_SHUTDOWN.equals(intentAction)
                                || Intent.ACTION_REBOOT.equals(intentAction))) {
                    ShutdownCheckPoints.recordCheckPoint(intentAction, callingPackage, null);
                }
            }

            int res;
            synchronized (mService.mGlobalLock) {
                final boolean globalConfigWillChange = mRequest.globalConfig != null
                        && mService.getGlobalConfiguration().diff(mRequest.globalConfig) != 0;
                final Task rootTask = mRootWindowContainer.getTopDisplayFocusedRootTask();
                if (rootTask != null) {
                    rootTask.mConfigWillChange = globalConfigWillChange;
                }
                ProtoLog.v(WM_DEBUG_CONFIGURATION, "Starting activity when config "
                        + "will change = %b", globalConfigWillChange);

                final long origId = Binder.clearCallingIdentity();

                res = resolveToHeavyWeightSwitcherIfNeeded();
                if (res != START_SUCCESS) {
                    return res;
                }
                res = executeRequest(mRequest);

                Binder.restoreCallingIdentity(origId);

                if (globalConfigWillChange) {
                    mService.mAmInternal.enforceCallingPermission(
                            android.Manifest.permission.CHANGE_CONFIGURATION,
                            "updateConfiguration()");
                    if (rootTask != null) {
                        rootTask.mConfigWillChange = false;
                    }
                    ProtoLog.v(WM_DEBUG_CONFIGURATION,
                                "Updating to new configuration after starting activity.");

                    mService.updateConfigurationLocked(mRequest.globalConfig, null, false);
                }
                final ActivityOptions originalOptions = mRequest.activityOptions != null
                        ? mRequest.activityOptions.getOriginalOptions() : null;
                final boolean newActivityCreated = mStartActivity == mLastStartActivityRecord;
                mSupervisor.getActivityMetricsLogger().notifyActivityLaunched(launchingState, res,
                        newActivityCreated, mLastStartActivityRecord, originalOptions);
                if (mRequest.waitResult != null) {
                    mRequest.waitResult.result = res;
                    res = waitResultIfNeeded(mRequest.waitResult, mLastStartActivityRecord,
                            launchingState);
                }
                return getExternalResult(res);
            }
        } finally {
            onExecutionComplete();
        }
    }

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