Application start Analysis Activity error in standard mode

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Application start Analysis Activity error in standard mode

In Androidthe start of the Activityruns in the corresponding task stack. If you directly Applicationto 标准模式start Activity, it will report the following error (Android7, except Android8, will be analyzed later):

Calling startActivity() from outside of an Activity  context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want?
at android.app.ContextImpl.startActivity(ContextImpl.java:912)
at android.app.ContextImpl.startActivity(ContextImpl.java:888)
at android.content.ContextWrapper.startActivity(ContextWrapper.java:379)

Error message prompted FLAG_ACTIVITY_NEW_TASKFlag of.

Activity in the call getApplication()or getApplicationContext(), eventually acquired are Application, then getApplication().startActivity()or getApplicationContext().startActivity()method in the Application

@Override
    public void startActivity(Intent intent) {
        mBase.startActivity(intent);
    }

Application of the method in startActivity years, passed mBaseto call startActivity, and mBase is ContextImpl. ContextImpl method of startActivity

@Override
    public void startActivity(Intent intent) {
        warnIfCallingFromSystemProcess();
        startActivity(intent, null);
    }

This method was calling another overloaded method

//Android6
@Override
    public void startActivity(Intent intent, Bundle options) {
        warnIfCallingFromSystemProcess();
        if ((intent.getFlags()&Intent.FLAG_ACTIVITY_NEW_TASK) == 0) {
            throw new AndroidRuntimeException(
                    "Calling startActivity() from outside of an Activity "
                    + " context requires the FLAG_ACTIVITY_NEW_TASK flag."
                    + " Is this really what you want?");
        }
        mMainThread.getInstrumentation().execStartActivity(
                getOuterContext(), mMainThread.getApplicationThread(), null,
                (Activity) null, intent, -1, options);
    }

Android6, at this method, we can see the exception in the previous thrown. In this judgment, if not increase FLAG_ACTIVITY_NEW_TASKthe Flag, it will throw an exception.

Look method Android7

@Override
    public void startActivity(Intent intent, Bundle options) {
        warnIfCallingFromSystemProcess();

        // Calling start activity from outside an activity without FLAG_ACTIVITY_NEW_TASK is
        // generally not allowed, except if the caller specifies the task id the activity should
        // be launched in.
        if ((intent.getFlags()&Intent.FLAG_ACTIVITY_NEW_TASK) == 0
                && options != null && ActivityOptions.fromBundle(options).getLaunchTaskId() == -1) {
            throw new AndroidRuntimeException(
                    "Calling startActivity() from outside of an Activity "
                    + " context requires the FLAG_ACTIVITY_NEW_TASK flag."
                    + " Is this really what you want?");
        }
        mMainThread.getInstrumentation().execStartActivity(
                getOuterContext(), mMainThread.getApplicationThread(), null,
                (Activity) null, intent, -1, options);
    }

It can be seen in Android7, relatively Android6, thrown also need to meet several other conditions. From the point of view startActivity Application method described above, Bundle type of the options parameter is null, so this condition is not satisfied, no exception is thrown.

Look method Android8

 @Override
    public void startActivity(Intent intent, Bundle options) {
        warnIfCallingFromSystemProcess();

        // Calling start activity from outside an activity without FLAG_ACTIVITY_NEW_TASK is
        // generally not allowed, except if the caller specifies the task id the activity should
        // be launched in.
        if ((intent.getFlags()&Intent.FLAG_ACTIVITY_NEW_TASK) == 0
                && options != null && ActivityOptions.fromBundle(options).getLaunchTaskId() == -1) {
            throw new AndroidRuntimeException(
                    "Calling startActivity() from outside of an Activity "
                    + " context requires the FLAG_ACTIVITY_NEW_TASK flag."
                    + " Is this really what you want?");
        }
        mMainThread.getInstrumentation().execStartActivity(
                getOuterContext(), mMainThread.getApplicationThread(), null,
                (Activity) null, intent, -1, options);
    }

And Android7 like also to determine the options, because the options is null, and therefore conditions are not met, it will not throw an exception.

Let's look at the method of Android9

@Override
    public void startActivity(Intent intent, Bundle options) {
        warnIfCallingFromSystemProcess();

        // Calling start activity from outside an activity without FLAG_ACTIVITY_NEW_TASK is
        // generally not allowed, except if the caller specifies the task id the activity should
        // be launched in. A bug was existed between N and O-MR1 which allowed this to work. We
        // maintain this for backwards compatibility.
        final int targetSdkVersion = getApplicationInfo().targetSdkVersion;

        if ((intent.getFlags() & Intent.FLAG_ACTIVITY_NEW_TASK) == 0
                && (targetSdkVersion < Build.VERSION_CODES.N
                        || targetSdkVersion >= Build.VERSION_CODES.P)
                && (options == null
                        || ActivityOptions.fromBundle(options).getLaunchTaskId() == -1)) {
            throw new AndroidRuntimeException(
                    "Calling startActivity() from outside of an Activity "
                            + " context requires the FLAG_ACTIVITY_NEW_TASK flag."
                            + " Is this really what you want?");
        }
        mMainThread.getInstrumentation().execStartActivity(
                getOuterContext(), mMainThread.getApplicationThread(), null,
                (Activity) null, intent, -1, options);
    }

In Android9, for options == null || with the judge, then ActivityOptions.fromBundle (options) .getLaunchTaskId () == -1, condition or will be set up, or will throw an exception.

It can be seen in Android7 and Android8, you can start directly in the Application Activity, without the need to increase the Flag FLAG_ACTIVITY_NEW_TASK.