Intent

阅读：http://developer.android.com/guide/components/intents-filters.html

 

intent可以用在：

1、Context.startActivity() or Activity.startActivityForResult() ；
2、Context.startService() 、Context.bindService() 。
3、Intent objects passed to any of the broadcast methods (such as Context.sendBroadcast(), Context.sendOrderedBroadcast(), or Context.sendStickyBroadcast()) 。

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其实intent就是一个包含了信息的bundle：

Component name：接受该intent的组件，这是可选的，确定了系统就自动去找组件，如果没有确定那么系统就根据其他的信息确定最好的接受组件

Action：你想要进行的操作；

Data：你要操作的对象的URI，一般与Action配对，但是很重要的一点就是，要设置它的MIME（使用SetType）

Category：要操作的组件的类型；

Extras：附带的一些参数数据，主要是键值对，有一些Action要求提供参数，而且添加参数的形式多种多样。

Flags：定义了组件该怎么显示；

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Only three aspects of an Intent object are consulted when the object is tested against an intent filter:

action
data (both URI and data type)
category

The extras and flags play no part in resolving which component receives an intent.

　　只有ACtion、data、category起到了过滤作用。

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<intent-filter . . . >
    <action android:name="com.example.project.SHOW_CURRENT" />
    <action android:name="com.example.project.SHOW_RECENT" />
    <action android:name="com.example.project.SHOW_PENDING" />
    . . .
</intent-filter>

一个组件可以有多个ACtion；要起到过滤作用，只要intent的action符合上面其中一个即可。

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<intent-filter . . . >
    <category android:name="android.intent.category.DEFAULT" />
    <category android:name="android.intent.category.BROWSABLE" />
    . . .
</intent-filter>

For an intent to pass the category test, every category in the Intent object must match a category in the filter. The filter can list additional categories, but it cannot omit any that are in the intent.

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<intent-filter . . . >
    <data android:mimeType="video/mpeg" android:scheme="http" . . . /> 
    <data android:mimeType="audio/mpeg" android:scheme="http" . . . />
    . . .
</intent-filter>

data的一般格式为：scheme://host:port/path，例如content://com.example.project:200/folder/subfolder/etc。

格式里的各部分都是可选的，但是必须按照顺序来，比如要有path，就得现有host等等。

系统的匹配也是从左往右的，先匹配scheme然后一个个来。

注意，属性里还能声明MIME type。

匹配规则：

1. An Intent object that contains neither a URI nor a data type passes the test only if the filter likewise does not specify any URIs or data types.

2. An Intent object that contains a URI but no data type (and a type cannot be inferred from the URI) passes the test only if its URI matches a URI in the filter and the filter likewise does not specify a type. This will be the case only for URIs like mailto: and tel: that do not refer to actual data.

3. An Intent object that contains a data type but not a URI passes the test only if the filter lists the same data type and similarly does not specify a URI.

4. An Intent object that contains both a URI and a data type (or a data type can be inferred from the URI) passes the data type part of the test only if its type matches a type listed in the filter. It passes the URI part of the test either if its URI matches a URI in the filter or if it has a content: or file: URI and the filter does not specify a URI. In other words, a component is presumed to support content: and file: data if its filter lists only a data type.

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<data android:mimeType="image/*" />

<data android:scheme="http" android:type="video/*" />

还有上面两种过滤条件，特别的是对于第二种，如果浏览器无法打开，那么就会调用ACtivity去接受这个DATA，如果Activity接受不了，则调用下载器下载。

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Therefore, the DEFAULT category is required for all filters — except for those with the MAIN action and LAUNCHER category. (Intent filters are not consulted for explicit intents.)

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文章最后有一个例子，可以作为参考使用。