Android项目生命周期 - 活动生命周期之前（Activity.onCreate（））

Question

I'm looking to implement a SQLite database in an Android project that I'm currently working on. To my surprise, it appears the only way to create this, is in the Activity code itself. (My last experience with Java and local databases was with Derby, which was a local file I had not created within the code.)

My question is, is there anything I can tap into that happens before the first Activity's onCreate()? I'll relate this back to Windows Form applications, where you can access Main() before launching the Form (Activity equivalent).

If I have to create the database within the program's code, I want to check to see if it already exists, only once, before the Activities start.

Answer 1

There is, but you don't need to. SQLite databases (which are built into Android) are just files on the local filesystem. Now you generally access them through either an ORM layer or through SQliteOpenHelper, which are Java interfaces to the database. When you open it, you just tell it where the file is. Generally you have a Singleton of the open helper or ORM layer class, so no per-Activity setup- you just throw any of that you need in the constructor there, and let the Singleton take care of it in whatever Activity ends up creating it.

Answer 2

The recommended way of using a database is to use SQLiteOpenHelper , which automatically creates it the first time you try to access it. (And also handles updates.)

Answer 3

您可以使用Application的onCreate方法在应用程序启动时（即在任何Activity之前）运行任何代码。