Dart Map<> 添加 元素

Map<String, WidgetBuilder> routesList() {

　　Map<String, WidgetBuilder> re = new Map<String, WidgetBuilder>();

　　　　for (var i = 0; i < RoutesData.key.length; i++) {

　　　　　　re.putIfAbsent(RoutesData.key[i], () => RoutesData.val[i]);

　　　　}

　　return re;

}

 

 

Map<String,String> map1 = {'a':'dart','b':'java'};

map1.putIfAbsent('c',()=>'C++');

 

putIfAbsent 用法：

/**

* Look up the value of [key], or add a new value if it isn't there.

*

* Returns the value associated to [key], if there is one.

* Otherwise calls [ifAbsent] to get a new value, associates [key] to

* that value, and then returns the new value.

*

* Map<String, int> scores = {'Bob': 36};

* for (var key in ['Bob', 'Rohan', 'Sophena']) {

* scores.putIfAbsent(key, () => key.length);

* }

* scores['Bob']; // 36

* scores['Rohan']; // 5

* scores['Sophena']; // 7

*

* Calling [ifAbsent] must not add or remove keys from the map.

*/

V putIfAbsent(K key, V ifAbsent());