From Hackmd : https://hackmd.io/jaW43Q3OTkCqnYJEU-NaWg?both

Outline

What is Retrofit?
Before start
Http libraries
Before start
Http libraries
OKhttp
Retrofit
Q&A

What is Retrofit?

Retrofit turns your HTTP API into a Java interface.

Before start

RESTful API
JSON
Gson
Annotation

RESTful API

rule or concept

每一個URI代表一種資源
客戶端通過四個HTTP動詞，對服務器端資源進行操作
```
@GET("users/list")
@GET("user/{userid}")
```

JSON & Gson

public static <T> T fromJson(String json, Class<T> klass) {
    return new Gson().fromJson(json, klass);
}

public static <T> List<T> fromJsonArray(String json, Class<T[]> klass) {
    T[] objects = new Gson().fromJson(json, klass);
    return objects == null ? new ArrayList<>() 
        : new ArrayList<T>(Arrays.asList(objects));
}

public static String toJson(Object object) {
    return new GsonBuilder()
            .create()
            .toJson(object);
}

public String toJson() {
    return new Gson().toJson(this);
}

Annotation

Usage

Dagger
Retrofit
Gson
DBflow
Butterknife

How to build Annotation

@Bind(R.id.text)  
TextView text;

build a Annotation class
write a Singleton class to handle TODO
inject the class when activity oncreate

preference : https://b013040034.github.io/ohmyblog/android/2018/02/06/annotation.html

Http libraries

HttpClient
OkHttp
Volley
retrofit

OKHttp

Find the bug 1

protected void onCreate(@Nullable Bundle savedInstanceState) {  
    super.onCreate(savedInstanceState);  
    setContentView(R.layout.activity_main);  
    try {  
        OkHttpClient client = new OkHttpClient();  
        String url = MessageFormat.format(ApiClient.Postal, 408);  
        final Request request = new Request.Builder()  
                .url(ApiClient.BASE_URL + url)  
                .build();  
        client.newCall(request).execute().body().string();  
    } catch (IOException e) {  
        e.printStackTrace();  
    }  
}

Error Msg 1

android.os.NetworkOnMainThreadException

Resolve 1

build a Singleton
init okhttp in constuctor
write a method to handle request

public void getData(String url, Callback callback) {  
    final Request request = new Request.Builder()  
            .url(BASE_URL + url)  
            .build();  
   client.newCall(request).enqueue(callback);  
}

Callback -> Find the bug 2

apiClient.getDataWithCallBack(url, new Callback() {  
    @Override  
    public void onFailure(Call call, final IOException e) { 
        text.setText(e.getMessage());  
   }  
  
    @Override  
    public void onResponse(Call call, Response response) throws IOException {  
        final String resStr = response.body().string();  
        text.setText(resStr);  
   }  
});  

Error Msg 2

Only the original thread that created a view hierarchy can touch its views.

AsyncTask

new AsyncTask<String, Void, String>() {  
    @Override  
    protected String doInBackground(String... urls) {  
        try {  
            return apiClient.getDataWithAsync(url);  
        } catch (IOException e) {  
            return e.getMessage();  
        }  
    }  
    @Override  
    protected void onPostExecute(String resStr) {  
        text.setText(resStr);  
    }  
};

Okhttp Conclusion

you have to make request in work thread or use callback
you have to change to ui thread after callback –> thread safe –> Encapsulation 封裝

Encapsulation

Volley vs Retrofit

Gson Get : call -> get object Post : make object -> call
Restful Api easy way to set url and data

What I expect

Lazy Lazy Lazy Lazy

No need to custom request -> No need to encapsulation
Api class looks like Api Document -> easy to find & add & fix api
get object and post object

Retrofit

dependencies

dependencies {
   compile 'com.squareup.retrofit2:retrofit:2.3.0'
   compile 'com.squareup.retrofit2:converter-gson:2.0.2'
}

Website

https://github.com/square/retrofit.

Singleton

public class ApiClient {
    public static final String BASE_URL = "https://api/";
    private static Retrofit retrofit = null;

    public static Retrofit getClient() {
        if (retrofit==null) {
            retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit;
    }
}

Api : Get

public interface ApiService {
    @GET("weather/{lat}/{lng}")
    Call<WeatherData> getWeather(@Path("lat") String lat, @Path("lng") String lng);
}

Api : Get (Volley and okHttp)

public static final String coordinate = "weather/{0}/{1}";
String url = MessageFormat.format(ApiClient.coordinate, lat, lng);

Convert json to Object

Website http://www.jsonschema2pojo.org/
Plugins

Object

public class WeatherData implements Serializable {
    @SerializedName("location")
    public String location;
    @SerializedName("temp")
    public float temperature;
}

You can use Kotlin + paracle instead

Get data

public void getWeatherData() {
        Retrofit retrofit = ApiClient.getClient();
        apiService = retrofit.create(ApiService.class);
        Call<WeatherData> data = apiService.getWeather("24","120");
        data.enqueue(new Callback<WeatherData>() {
            @Override
            public void onResponse(Call<WeatherData> call, Response<WeatherData> response) {
                WeatherData weatherData = response.body();
            }
            @Override
            public void onFailure(Call<WeatherData> call, Throwable t) {
             
            }
        });
    }

Api : Post

public interface ApiService {
    @POST("AccessToken")  
    Call<AccessToken> getTokenDebug(@Body AccessTokenInput tokenInput);

}

Post data

Call<AccessToken> dataDebug = apiService.getTokenDebug(accessToken);
dataDebug.enqueue(new Callback<AccessToken>() {  
    @Override  
    public void onResponse(Call<AccessToken> call, Response<AccessToken> response) {  
        AccessToken accessToken = response.body();  
        caculateResult(accessToken, textResultDebug);   
    }  
    @Override  
    public void onFailure(Call<AccessToken> call, Throwable t) {  
        textResultDebug.setText(t.getMessage());  
    }  
});

Api : Post (Volley)

StringRequest : with param
JsonObjectRequest : with json

Query String

@GET("news")
Call<News> getItem(@Query("type") String type);

@GET("news")
Call<News> getItem(@QueryMap Map<String, String> map);

Post with field

@FormUrlEncoded
@POST("news")
Call<User> postItem(@Field("type") String type);

@FormUrlEncoded
@POST("news")
Call<User> postItem(@FieldMap Map<String, String> map);

Other features

簽名 : Signature
標頭 : Headers
檔案 : Multipart

signature

https://github.com/square/okhttp/wiki/Interceptors

Multipart

https://chenkaihua.com/2016/04/02/retrofit2-upload-multipart-files/

perference

http://square.github.io/retrofit/ https://ihower.tw/blog/archives/1542 https://itw01.com/V33WE9D.html https://bng86.gitbooks.io/android-third-party-/content/retrofit.html

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