AppStateIOS 可以告诉你应用程序是在前台还是在后台，而且状态更新时会通知你。 在处理推送通知时，AppStateIOS 经常被用于判断目标和适当的行为。
Active – 应用程序在前台运行
Background – 应用程序在后台运行。用户正在使用另一个应用程序或者在主屏幕上。
Inactive – 这是一种过渡状态，目前不会在React Native的应用程序上发生。
想要获取更多的信息，见 Apples documentation
为了查看当前的状态，你可以检查 AppStateIOS.currentState，该方法会一直保持最新状态。然而，当 AppStateIOS在桥接器上检索currentState时，在启动时它将会为空。
getInitialState: function() {
return {
currentAppState: AppStateIOS.currentState,
};
}, componentDidMount: function() {
AppStateIOS.addEventListener(change, this._handleAppStateChange);
}, componentWillUnmount: function() {
AppStateIOS.removeEventListener(change, this._handleAppStateChange);
}, _handleAppStateChange: function(currentAppState) {
this.setState({ currentAppState, });
}, render: function() {
return (
<Text>Current state is: {this.state.currentAppState}</Text>
);
}, 这个例子似乎只能说”当前状态是：活跃的”因为在 active 状态时，应用程序只对用户是可见的，空状态只能是暂时的。
static addEventListener(type: string, handler: Function)
通过监听 change 事件类型和提供处理程序，为应用程序状态变化添加一个处理程序。
static removeEventListener(type: string, handler: Function)
通过传递 change 事件类型和处理程序，删除一个处理程序。
use strict; var React = require(react-native); var {
AppStateIOS,
Text,
View
} = React; var AppStateSubscription = React.createClass({
getInitialState() { return {
appState: AppStateIOS.currentState,
previousAppStates: [],
};
},
componentDidMount: function() {
AppStateIOS.addEventListener(change, this._handleAppStateChange);
},
componentWillUnmount: function() {
AppStateIOS.removeEventListener(change, this._handleAppStateChange);
},
_handleAppStateChange: function(appState) { var previousAppStates = this.state.previousAppStates.slice();
previousAppStates.push(this.state.appState); this.setState({
appState,
previousAppStates,
});
},
render() { if (this.props.showCurrentOnly) { return ( <View>
<Text>{this.state.appState}</Text>
</View>
);
} return ( <View>
<Text>{JSON.stringify(this.state.previousAppStates)}</Text>
</View>
);
}
});
exports.title = AppStateIOS;
exports.description = iOS app background status;
exports.examples = [
{
title: AppStateIOS.currentState,
description: Can be null on app initialization,
render() { return <Text>{AppStateIOS.currentState}</Text>; }
},
{
title: Subscribed AppStateIOS:,
description: This changes according to the current state, so you can only ever see it rendered as "active",
render(): ReactElement { return <AppStateSubscription showCurrentOnly={true} />; }
},
{
title: Previous states:,
render(): ReactElement { return <AppStateSubscription showCurrentOnly={false} />; }
},
];