intent的理解

An intent is an abstract description of an operation to be performed. It can be used with startActivity to launch an Activity, broadcastIntent to send it to any interested BroadcastReceiver components, and startService(Intent) or bindService(Intent, ServiceConnection, int) to communicate with a background Service.

intent是对一个可以进行的操作的抽象描述。它可以用来启动一个activity，或是广播道任何接受它的广播组建。并且它可以启动一个服务或是绑定到到一个服务来和一个后台服务通信。

An Intent provides a facility for performing late runtime binding between the code in different applications. Its most significant use is in the launching of activities, where it can be thought of as the glue between activities. It is basically a passive data structure holding an abstract description of an action to be performed. The primary pieces of information in an intent are:

action -- The general action to be performed, such as ACTION_VIEW, ACTION_EDIT, ACTION_MAIN, etc.
data -- The data to operate on, such as a person record in the contacts database, expressed as a Uri.

Some examples of action/data pairs are:

ACTION_VIEW content://contacts/people/1 -- Display information about the person whose identifier is "1".
ACTION_EDIT content://contacts/people/1 -- Edit information about the person whose identifier is "1".

In addition to these primary attributes, there are a number of secondary attributes that you can also include with an intent:
除了上面的action和data属性之外，action还有一些二级属性可供使用
category -- Gives additional information about the action to execute. For example, CATEGORY_LAUNCHER means it should appear in the Launcher as a top-level application, while CATEGORY_ALTERNATIVE means it should be included in a list of alternative actions the user can perform on a piece of data.
type -- Specifies an explicit type (a MIME type) of the intent data. Normally the type is inferred from the data itself. By setting this attribute, you disable that evaluation and force an explicit type.
component -- Specifies an explicit name of a component class to use for the intent. Normally this is determined by looking at the other information in the intent (the action, data/type, and categories) and matching that with a component that can handle it. If this attribute is set then none of the evaluation is performed, and this component is used exactly as is. By specifying this attribute, all of the other Intent attributes become optional.
extras -- This is a Bundle of any additional information. This can be used to provide extended information to the component. For example, if we have a action to send an e-mail message, we could also include extra pieces of data here to supply a subject, body, etc.