为什么Android7.0和8.0上ApplicationContext.startActivty(...)不需要添加FLAG_ACTIVITY_NEW_TASK呢？

小编 2026-07-02 阅读:499 评论:0

我们都知道在Android7.0之前，非Activity环境中（例如ApplicationContext）启动Activity需要添加FLAG_ACTIVITY_NEW_TASK标记位，才会正...

我们都知道在Android7.0之前，非Activity环境中（例如ApplicationContext）启动Activity需要添加FLAG_ACTIVITY_NEW_TASK标记位，才会正常启动Activity。因为非Activity的环境中并没有所谓的任务栈。

但是，最近在项目中发现，在Android7.0和8.0上并不需要添加FLAG_ACTIVITY_NEW_TASK标记位也可以正常启动Activity，在Android9.0的官方文档上又强制要求添加了。我们来看看官网是怎么说的：

在Android 9 中，你不能从非Activity环境中启动Activity，除非您传递Intent标志FLAG_ACTIVITY_NEW_TASK。如果您尝试在不传递此标志的情况下启动Activity，则该Activity不会启动，系统会在日志中输出一则消息。在Android 7.0之前，标志要求一直是期望的行为并被强制执行。Android7.0中的一个错误会临时阻止实施标志要求。

看最后一句：“Android7.0中的一个错误会临时阻止实施标志要求”。难道是谷歌的一个BUG？我们来查看源码(frameworks/base/core/java/android/app/ContextImpl.java)看看：

首先看看Android6.0上的写法

@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);
}

Android 7.0～Android8.0

 @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);
}

Android 9.0以上修复了这个问题，强制执行

@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);
}