Retrofit学习笔记

Retrofit:  与okhttp共同出自于Square公司，retrofit就是对okhttp做了一层封装，把网络请求都交给了OkHttp,只需要通过简单的配置就能使用其来进行网络请求。

使用Retrofit的准备工作

１．添加Retrofit依赖

compile 'com.squareup.retrofit2:retrofit:2.1.0'

２．添加响应转换器依赖，Retrofit默认不集成响应转换器的

compile 'com.squareup.retrofit2:converter-gson:2.1.0'

最后不要忘了，声明网络请求的权限

开始创建Retrofit

步骤一：

Retrofit将HTTP API转化为了接口的形式，因此，我们提供如下接口：

public interface HttpJson {   @GET    Call<Apps> getAppLists(@Url String url);}

步骤二：

 Retrofit retrofit = new Retrofit.Builder()                .addConverterFactory(GsonConverterFactory.create())                .baseUrl(UrlPath)                .build();        httpJson = retrofit.create(HttpJson.class);        Call<Apps> appLists = httpJson.getAppLists(UrlPath);

addConverterFactory()为了添加json 解析工具

baseUrl()注意：只能传入以/结尾的网址

httpJson　接口 的一个具体实现，

步骤三

得到call对象，并且可以使用enqueue 或者 execute来执行发起请求，enqueue是是异步执行，而 execute是同步执行。

 appLists.enqueue(new Callback<Apps>() {            @Override            public void onResponse(Call<Apps> call, Response<Apps> response) {                if(response.body() !=null) {　                    Log.d("LXM", response.body()+ "");                }                else{                    Log.d("LXM","response is null");                }            }            @Override            public void onFailure(Call<Apps> call, Throwable t) {                Log.d("LXM",t.getMessage());            }        });

我们所请求的数据，都会在response.body()中返回

问题总结

1.Base URL required

出现这个错误是因为，Base URL为空，这是因为源码在构建的过程中，会检查　Base URL,如果Base URL为空，则会抛出这个异常

2.java.lang.IllegalArgumentException: baseUrl must end in /:

Base URL规定，它最后一定要以／结尾

我们知道，很多时候，我们的网址掺杂了很多参数，是无法做到／结尾的，此时，我们要借助＠URL,如下：

public interface HttpJson {   @GET    Call<Apps> getAppLists(@Url String url);}

注意：＠GET在这里是没有任何参数,当使用了@URL时，会默认使用传进来的URL的参数，这个特殊的用法可以支持URL是动态变化的情况，并且解决了Base URL必须以／结尾的规定

3. Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 2 path $

Json数据为嵌套形式时，对象抽取不当，如下

{ "ret": "0", "data": { "appList": [ { "fileSize": "12431425", "appName": "贝瓦儿歌", "icon": "http://img.sky.fs.skysrt.com///uploads/20160607/20160607140722707425.png", "appRunType": 0},{ "fileSize": "14022612", "appName": "逸趣休闲", "icon": "http://img.sky.fs.skysrt.com///uploads/20161022/20161022144435531698.png", "appRunType": 0}, { "fileSize": "14047310", "appName": "风尚舞汇", "icon": "http://img.sky.fs.skysrt.com///uploads/20161022/20161022144303406615.png", "appRunType": 0}, { "fileSize": "1271215", "appName": "精华E课堂", "icon": "http://img.sky.fs.skysrt.com///uploads/20140705/20140705094119947612.png", "appRunType": 0}], 　"total": ４, "count": ４, 　"page": 1 }, "msg": "success" }

我们可以看到，这个json文件中最外层，有三个对象，分别是"ret","data","msg"

而"data"对象又包含四个对象"appList","total",count","page"

其中，appList对象的值是一组数组，此时，要想正确获取对象值，需要三个类

APPS，包含"ret","data","msg"对象

APPListmsg,　包含"appList","total",count","page"，

AppList.为“data”数组中单项的对象类

代码如下

json最外层的数据结构

public class Apps {    private String ret;    private APPListmsg data;    private String msg;        public void setData(AppLists data) {        this.data = data;    }    public AppLists getData() {        return data;    }    public void setRet(String ret) {        this.ret = ret;    }    public String getRet() {        return ret;    }    public void setMsg(String msg) {        this.msg = msg;    }    public String getMsg() {        return msg;    }}

数组中数据的数据结构

public class AppList {    private String fileSize;    private String appName;    private String icon;    private String appRunType;    public AppList(){}    public AppList(String fileSize, String appName, String icon, String appRunType){        this.fileSize = fileSize;        this.appName = appName;        this.icon = icon;        this.appRunType = appRunType;    }　    public String getAppRunType() {        return appRunType;    }    public void setAppRunType(String appRunType) {        this.appRunType = appRunType;    }    public String getIcon() {        return icon;    }    public void setIcon(String icon) {        this.icon = icon;    }    public String getFileSize() {        return fileSize;    }    public void setFileSize(String fileSize) {        this.fileSize = fileSize;    }    public String getAppName() {        return appName;    }    public void setAppName(String appName) {        this.appName = appName;    }}

data对象的数据结构

public class APPListmsg  {    private List<AppList> appList;    public List<AppList> getAppList() {        return appList;    }    public void setAppLists(List<AppList> appList) {        this.appList = appList;    }}

范例代码如下：

 public void test3(){        Retrofit retrofit = new Retrofit.Builder()                .addConverterFactory(GsonConverterFactory.create())                .baseUrl(UrlPath)                .build();        httpJson = retrofit.create(HttpJson.class);        Call<Apps> appLists = httpJson.getAppLists(UrlPath);        appLists.enqueue(new Callback<Apps>() {            @Override            public void onResponse(Call<Apps> call, Response<Apps> response) {                if(response.body() !=null) {                    List<AppList> apps = response.body().getData().getAppList();                    Log.d("LXM", apps + "");                    for (int i = 0; i < apps.size(); i++) {                        Log.d("LXM", apps.get(i).getAppName());                    }                }                else{                    Log.d("LXM","response is null");                }            }            @Override            public void onFailure(Call<Apps> call, Throwable t) {                Log.d("LXM",t.getMessage());            }        });    }