一，今天完成的事情

最近做任务发现有很多知识点没有完全掌握然而就

所以重新复习了一下关于angular2Http请求的几种方法

1. 1.HttpClient Get请求。

   1. 导入HttpClient ， @angular/common/http
   2. component 构造函数中注入HttpClient
   3. 使用.get（端点）方法创建HTTP GET请求

   4. 订阅(Subscribe )返回的observable并显示结果

   5.  constructor(private httpClient:HttpClient) { }

   6.  ngOnInit() {//初始化时就开始get请求数据

   7. this.customersObservable = this.httpClient    .get<Customer[]>("127.0.0.1:3000/customers"); } }

2. 2.HTTP GET 请求参数: HttpParams
   
   1. 请求第1页，最大条数2：
      
      1. url方式
         http://127.0.0.1:3000/customers?_page=1&_limit=1
      2. 使用httpClient实现
         
         1. 导入HttpParams
            import {HttpParams} from "@angular/common/http";
         2. 构建一个 HttpParams 对象
            const params = new HttpParams().set('_page', "1").set('_limit', "1");
         3. 呼叫 .get() 方法并携带参数，然后将返回的 Observable 对象分配给customersObservable。
         4. （params 要与get在同一个方法中）
            this.customersObservable = this.httpClient.get("http://127.0.0.1:3000/customers", {params});
         5. 使用更简单的方法新建HttpParams对象：【fromString】
            const params = new HttpParams({fromString: '_page=1&_limit=1'});
      3. 带参Get请求（记url QueryString）
         
const params = new HttpParams({fromString: '_page=1&_limit=1'});
this.customersObservable = this.http
.request("GET","http://127.0.0.1:3000/customers",
{
responseType:"json",
params
});

3. 添加 HTTP Headers
   
   1. 导入HttpHeaders
      import { HttpHeaders } from '@angular/common/http';
   2. 新建客制的HttpHeader对象
      const headers = new HttpHeaders().set("X-CustomHttpHeader", "CUSTOM_VALUE");
   3. 发送带httpHeader的请求
      
const headers = new HttpHeaders().set("X-CustomHttpHeader", "CUSTOM_VALUE");
this.customersObservable = this.httpClient.get("http://127.0.0.1:3000/customers", {headers});

   4. 携带httpHeader，会出现重复请求的状况，第一次Option请求 204状态（Firefox 为Option请求方法），第二次为返回的结果。
4. 3.发送HTTP PUT 请求
   HTTP PUT 方法用来完全替换 API server上的资源。用HttpClient 发送PUT 请求替换Customers上id为1的资源:
   
this.httpClient.put("http://127.0.0.1:3000/customers/1",
{
"name": "NewCustomer001",
"email": "newcustomer001@email.com",
"tel": "0000252525"
})
.subscribe(
data => {
console.log("PUT Request is successful ", data);
},
error => {
console.log("Rrror", error);
}
);

5. 4.发送HTTP PATCH 请求
   HTTP PATCH 用来更新API server上的资源。
   this.httpClient.patch("http://127.0.0.1:3000/customers/1",
{
"email": "newcustomer001@gmail.com"
})
.subscribe(
data => {
console.log("PUT Request is successful ", data);
},
error => {
console.log("Error", error);
}
);

6. 5.发送HTTP DELETE 请求
   HTTP DELETE 用来删除 API server上的资源
   this.httpClient.delete("http://127.0.0.1:3000/customers/1")
.subscribe(
data => {
console.log("DELETE Request is successful ", data);
},
error => {
console.log("Error", error);
}
);

7. 6.发送 HTTP POST 请求
   HTTP POST 方法有很多用途，大多数是用来在API server上新增一笔数据。
   this.httpClient.post("http://127.0.0.1:3000/customers",
{
"name": "Customer004",
"email": "customer004@email.com",
"tel": "0000252525"
})
.subscribe(
data => {
console.log("POST Request is successful ", data);
},
error => {
console.log("Error", error);
}
);

二，明天计划做下编辑页面的数据获取