How do I pass data between Activities/Services within a sing

How do I pass data between Activities/Services within a single application?

It depends on the type of data that you want to share:

Primitive Data Types

To share primitive data between Activities/Services in an application,use Intent.putExtras(). For passing primitive data that needs to persist use thePreferencesstorage mechanism.

Non-Persistent Objects

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 asgetInstance()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 usepublic staticfields 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 theData Storagefor further details on how to use these components.

（编辑：李大同）

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