Intent的定义及用法

1. 什么Intent

google官方解释

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.

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.

大概意思：Intent是用于组件之间的跳转，通过startActivity启动Activity；通过sendBroadCast发送广播给相应的BroadcastReceiver；通过startService或bindService(Intent,ServiceConnection,int)和后台service交互。

2. Intent的用法

以启动Activity为例，分为显式调用和隐式调用

1、显示调用

Intent intent = new Intent(MainActivity.this, NormalActivity.class);
startActivity(intent);

查看Intent的构造函数

public Intent(Context packageContext, Class<?> cls) {
mComponent = new ComponentName(packageContext, cls);

将需要启动的Activity的类名传进去了。

2、隐式调用

应用场景，不能明确知道需要启动的Activity的类名，比如启动系统默认的浏览器、打电话、进入拨号界面等

主要是通过Action、Data、Category等属性实现

例如：

进入拨号界面：

Intent intent = new Intent(Intent.ACTION_DIAL);
startActivity(intent);

也可以携带电话号码：

Intent intent = new Intent(Intent.ACTION_DIAL, Uri.parse("tel:123"));
startActivity(intent);

自定义Action：

定义IntentFilter，在manifest.xml中定义

<activity               android:name="com.example.intenttest.ActionActivity">
<intent-filter >
<action android:name="com.example.actionstart" />
<category     android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>

sendIntent：

Intent intent = new Intent("com.example.actionstart");
startActivity(intent);