Android P预览版中onStart先于onActivityResult执行的疑问

Great question—this is exactly the kind of behavior shift you might encounter when testing early platform previews, and it’s easy to confuse with a bug at first glance. Let’s break this down clearly:

1. This is an Intentional Platform Change, Not a Bug #

The adjusted lifecycle order (onStart() → onActivityResult() → onResume()) that you’re seeing in Android P preview builds (and later the official Android 9 Pie release) is a deliberate change from the Android team, not an oversight.

2. Rationale Behind the Shift #

Prior to Android P, the order (onActivityResult() → onStart() → onResume()) could lead to edge cases, especially with launch modes like singleTask (your Activity A’s mode) or singleTop:

• If Activity A was in a stopped state when returning from B, processing the result before onStart() meant you might be interacting with uninitialized views or state that hadn’t been restored yet.
• The new order aligns with core lifecycle semantics: onStart() signals that the Activity is about to become visible and has restored its basic state. Processing the result after this ensures your app is in a stable state to handle the returned data.

3. Official Documentation & Confirmation #

While early preview docs might have been lagging, the official Android 9 Pie documentation now clarifies this updated order:

• onActivityResult() is guaranteed to execute after onStart() but before onResume() when returning to an Activity from startActivityForResult().
• This change is also noted in the Android 9 behavior changes guide, framed as a consistency improvement for task stack operations and lifecycle reliability.

4. Actionable Advice for Your Code #

Since your app uses targetSdkVersion 23, you’ll want to adjust any logic that relied on the old order:

• Avoid assuming onStart() has already run when onActivityResult() is called (this was the case pre-P, but not anymore).
• Move view initialization or state restoration code needed for handling results into onCreate() or ensure it’s completed in onStart() before onActivityResult() runs.
• If updating UI based on the result, double-check that views are fully initialized (e.g., avoid calling findViewById() in onActivityResult() unless you’ve confirmed onStart() has executed).

内容的提问来源于stack exchange，提问作者Fadi Selim