For sharing complex non-persistent user-defined objects for short
duration, the following approaches are recommended:
Singleton class
You can take advantage of the fact that your application components
run in the same process through the use of a singleton. This is a
class that is designed to have only one instance. It has a static
method with a name such as getInstance() that returns the instance;
the first time this method is called, it creates the global instance.
Because all callers get the same instance, they can use this as a
point of interaction. For example activity A may retrieve the instance
and call setValue(3); later activity B may retrieve the instance and
call getValue() to retrieve the last set value.
A public static field/method
An alternate way to make data accessible across Activities/Services is
to use public static fields and/or methods. You can access these
static fields from any other class in your application. To share an
object, the activity which creates your object sets a static field to
point to this object and any other activity that wants to use this
object just accesses this static field.
A HashMap of WeakReferences to Objects
You can also use a HashMap of WeakReferences to Objects with Long
keys. When an activity wants to pass an object to another activity, it
simply puts the object in the map and sends the key (which is a unique
Long based on a counter or time stamp) to the recipient activity via
intent extras. The recipient activity retrieves the object using this
key.
Persistent Objects
Even while an application appears to continue running, the system may
choose to kill its process and restart it later. If you have data that
you need to persist from one activity invocation to the next, you need
to represent that data as state that gets saved by an activity when it
is informed that it might go away.
For sharing complex persistent user-defined objects, the following
approaches are recommended:
Application Preferences
Files
contentProviders
SQLite DB
If the shared data needs to be retained across points where the
application process can be killed, then place that data in persistent
storage like Application Preferences, SQLite DB, Files or
ContentProviders. Please refer to the Data Storage for further details
on how to use these components.
static
而不是final
(或者实际上是static final
)吗? - zapl