Flutter-- Map、Class转json，json解析

class Model {
 
  int key;
  String value;
 
  Model(this.key, this.value);
 
  String toJson() {
    Map<String, dynamic> all = {};
    all["key"] = key;
    all["value"] = value;
    return jsonEncode(all);
  }
  
  static Model fromJson(String jsonData) {
    Map<String, dynamic> all = jsonDecode(jsonData) as Map<String, dynamic>;
    int key = all["key"];
    String value = all["value"];
    return Model(key, value);
  }
 
}

需要注意的是，map的Key不可以是String以外的类型，不然会报错

Unhandled Exception: Converting object to an encodable object failed: