activity的启动流程

 @Override
    public void startActivity(Intent intent, @Nullable Bundle options) {
        if (options != null) {
            startActivityForResult(intent, -1, options);
        } else {
            // Note we want to go through this call for compatibility with
            // applications that may have overridden the method.
            startActivityForResult(intent, -1);
        }
    }

  public void startIntentSenderForResult(IntentSender intent, int requestCode,
            Intent fillInIntent, int flagsMask, int flagsValues, int extraFlags)
            throws IntentSender.SendIntentException {
        if (mParent == null) {
            startIntentSenderForResultInner(intent, requestCode, fillInIntent,
                    flagsMask, flagsValues, this);
        } else {
            mParent.startIntentSenderFromChild(this, intent, requestCode,
                    fillInIntent, flagsMask, flagsValues, extraFlags);
        }
    }




 private void startIntentSenderForResultInner(IntentSender intent, int requestCode,
            Intent fillInIntent, int flagsMask, int flagsValues, Activity activity)
            throws IntentSender.SendIntentException {
        try {
            String resolvedType = null;
            if (fillInIntent != null) {
                resolvedType = fillInIntent.resolveTypeIfNeeded(getContentResolver());
            }
            int result = ActivityManagerNative.getDefault()
                .startActivityIntentSender(mMainThread.getApplicationThread(), intent,
                        fillInIntent, resolvedType, mToken, activity.mEmbeddedID,
                        requestCode, flagsMask, flagsValues);
            if (result == IActivityManager.START_CANCELED) {
                throw new IntentSender.SendIntentException();
            }
            Instrumentation.checkStartActivityResult(result, null);
        } catch (RemoteException e) {
        }
        if (requestCode >= 0) {
            // If this start is requesting a result, we can avoid making
            // the activity visible until the result is received.  Setting
            // this code during onCreate(Bundle savedInstanceState) or onResume() will keep the
            // activity hidden during this time, to avoid flickering.
            // This can only be done when a result is requested because
            // that guarantees we will get information back when the
            // activity is finished, no matter what happens to it.
            mStartedActivity = true;
        }
    }

public ActivityResult execStartActivity(
        Context who, IBinder contextThread, IBinder token, Activity target,
        Intent intent, int requestCode) {
        IApplicationThread whoThread = (IApplicationThread) contextThread;
        if (mActivityMonitors != null) {
            synchronized (mSync) {
                final int N = mActivityMonitors.size();
                for (int i=0; i<N; i++) {
                    final ActivityMonitor am = mActivityMonitors.get(i);
                    if (am.match(who, null, intent)) {
                        am.mHits++;
                        if (am.isBlocking()) {
                            return requestCode >= 0 ? am.getResult() : null;
                        }
                        break;
                    }
                }
            }
        }
        try {
            int result = ActivityManagerNative.getDefault()
                .startActivity(whoThread, intent,
                        intent.resolveTypeIfNeeded(who.getContentResolver()),
                        null, 0, token, target != null ? target.mEmbeddedID : null,
                        requestCode, false, false);
            checkStartActivityResult(result, intent);
        } catch (RemoteException e) {
        }
        return null;
    }

private static void checkStartActivityResult(int res, Object intent) {
        if (res >= IActivityManager.START_SUCCESS) {
            return;
        }

        switch (res) {
            case IActivityManager.START_INTENT_NOT_RESOLVED:
            case IActivityManager.START_CLASS_NOT_FOUND:
                if (intent instanceof Intent && ((Intent)intent).getComponent() != null)
                    throw new ActivityNotFoundException(
                            "Unable to find explicit activity class "
                            + ((Intent)intent).getComponent().toShortString()
                            + "; have you declared this activity in your AndroidManifest.xml?");
                throw new ActivityNotFoundException(
                        "No Activity found to handle " + intent);
            case IActivityManager.START_PERMISSION_DENIED:
                throw new SecurityException("Not allowed to start activity "
                        + intent);
            case IActivityManager.START_FORWARD_AND_REQUEST_CONFLICT:
                throw new AndroidRuntimeException(
                        "FORWARD_RESULT_FLAG used while also requesting a result");
            case IActivityManager.START_NOT_ACTIVITY:
                throw new IllegalArgumentException(
                        "PendingIntent is not an activity");
            default:
                throw new AndroidRuntimeException("Unknown error code "
                        + res + " when starting " + intent);
        }
    }

 public final int startActivity(IApplicationThread caller,
            Intent intent, String resolvedType, Uri[] grantedUriPermissions,
            int grantedMode, IBinder resultTo,
            String resultWho, int requestCode, boolean onlyIfNeeded,
            boolean debug) {
        return startActivityMayWait(caller, intent, resolvedType,
                grantedUriPermissions, grantedMode, resultTo, resultWho,
                requestCode, onlyIfNeeded, debug, null, null);
    }

    public final WaitResult startActivityAndWait(IApplicationThread caller,
            Intent intent, String resolvedType, Uri[] grantedUriPermissions,
            int grantedMode, IBinder resultTo,
            String resultWho, int requestCode, boolean onlyIfNeeded,
            boolean debug) {
        WaitResult res = new WaitResult();
        startActivityMayWait(caller, intent, resolvedType,
                grantedUriPermissions, grantedMode, resultTo, resultWho,
                requestCode, onlyIfNeeded, debug, res, null);
        return res;
    }





    private final int startActivityMayWait(IApplicationThread caller,
            Intent intent, String resolvedType, Uri[] grantedUriPermissions,
            int grantedMode, IBinder resultTo,
            String resultWho, int requestCode, boolean onlyIfNeeded,
            boolean debug, WaitResult outResult, Configuration config) {
        // Refuse possible leaked file descriptors
        if (intent != null && intent.hasFileDescriptors()) {
            throw new IllegalArgumentException("File descriptors passed in Intent");
        }

        final boolean componentSpecified = intent.getComponent() != null;

        // Don't modify the client's object!
        intent = new Intent(intent);

        // Collect information about the target of the Intent.
        ActivityInfo aInfo;
        try {
            ResolveInfo rInfo =
                ActivityThread.getPackageManager().resolveIntent(
                        intent, resolvedType,
                        PackageManager.MATCH_DEFAULT_ONLY
                        | STOCK_PM_FLAGS);
            aInfo = rInfo != null ? rInfo.activityInfo : null;
        } catch (RemoteException e) {
            aInfo = 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
            if (debug) {
                if (!aInfo.processName.equals("system")) {
                    setDebugApp(aInfo.processName, true, false);
                }
            }
        }

        synchronized (this) {
            int callingPid;
            int callingUid;
            if (caller == null) {
                callingPid = Binder.getCallingPid();
                callingUid = Binder.getCallingUid();
            } else {
                callingPid = callingUid = -1;
            }

            mConfigWillChange = config != null && mConfiguration.diff(config) != 0;
            if (DEBUG_CONFIGURATION) Slog.v(TAG,
                    "Starting activity when config will change = " + mConfigWillChange);

            final long origId = Binder.clearCallingIdentity();

            int res = startActivityLocked(caller, intent, resolvedType,
                    grantedUriPermissions, grantedMode, aInfo,
                    resultTo, resultWho, requestCode, callingPid, callingUid,
                    onlyIfNeeded, componentSpecified);

            if (mConfigWillChange) {
                // If the caller also wants to switch to a new configuration,
                // do so now.  This allows a clean switch, as we are waiting
                // for the current activity to pause (so we will not destroy
                // it), and have not yet started the next activity.
                enforceCallingPermission(android.Manifest.permission.CHANGE_CONFIGURATION,
                        "updateConfiguration()");
                mConfigWillChange = false;
                if (DEBUG_CONFIGURATION) Slog.v(TAG,
                        "Updating to new configuration after starting activity.");
                updateConfigurationLocked(config, null);
            }

            Binder.restoreCallingIdentity(origId);

            if (outResult != null) {
                outResult.result = res;
                if (res == IActivityManager.START_SUCCESS) {
                    mWaitingActivityLaunched.add(outResult);
                    do {
                        try {
                            wait();
                        } catch (InterruptedException e) {
                        }
                    } while (!outResult.timeout && outResult.who == null);
                } else if (res == IActivityManager.START_TASK_TO_FRONT) {
                    HistoryRecord r = this.topRunningActivityLocked(null);
                    if (r.nowVisible) {
                        outResult.timeout = false;
                        outResult.who = new ComponentName(r.info.packageName, r.info.name);
                        outResult.totalTime = 0;
                        outResult.thisTime = 0;
                    } else {
                        outResult.thisTime = SystemClock.uptimeMillis();
                        mWaitingActivityVisible.add(outResult);
                        do {
                            try {
                                wait();
                            } catch (InterruptedException e) {
                            }
                        } while (!outResult.timeout && outResult.who == null);
                    }
                }
            }

            return res;
        }
    }