LiveData adapter for Retrofit

README.md

LiveData Adapter for Retrofit

Copy the following classes in your project to use LiveData<ApiResponse<T>> instead of Call<T> in Retrofit services. Made this gist so everyone can just copy and paste them in project rather than finding through the Google Samples.

Original Credits: I didn't make these classes, they are from Google Sample

Difference

Traditional way - with Call:

interface SomeService {

    @GET("data")
    fun getData(): Call<T>
}

Traditional way - with LiveData:

interface SomeService {

    @GET("data")
    fun getData(): LiveData<ApiResponse<T>>
}

Usage

Set the LiveDataCallAdapterFactory in the Retrofit Builder

Retrofit.Builder()
        .baseUrl(BASE_URL)
        // ....
        .addCallAdapterFactory(LiveDataCallAdapterFactory())
        // ....
        .build()

ApiResponse.java

import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.util.ArrayMap;

import java.io.IOException;
import java.util.Collections;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import retrofit2.Response;

/**
 * Common class used by API responses.
 *
 * @param <T>
 */
public class ApiResponse<T> {
    private static final Pattern LINK_PATTERN = Pattern
            .compile("<([^>]*)>[\\s]*;[\\s]*rel=\"([a-zA-Z0-9]+)\"");
    private static final Pattern PAGE_PATTERN = Pattern.compile("page=(\\d)+");
    private static final String NEXT_LINK = "next";
    public final int code;
    @Nullable
    public final T body;
    @Nullable
    public final String errorMessage;
    @NonNull
    public final Map<String, String> links;

    public ApiResponse(Throwable error) {
        code = 500;
        body = null;
        errorMessage = error.getMessage();
        links = Collections.emptyMap();
    }

    public ApiResponse(Response<T> response) {
        code = response.code();
        if (response.isSuccessful()) {
            body = response.body();
            errorMessage = null;
        } else {
            String message = null;
            if (response.errorBody() != null) {
                try {
                    message = response.errorBody().string();
                } catch (IOException ignored) {
                    Timber.e(ignored, "error while parsing response");
                }
            }
            if (message == null || message.trim().length() == 0) {
                message = response.message();
            }
            errorMessage = message;
            body = null;
        }
        String linkHeader = response.headers().get("link");
        if (linkHeader == null) {
            links = Collections.emptyMap();
        } else {
            links = new ArrayMap<>();
            Matcher matcher = LINK_PATTERN.matcher(linkHeader);

            while (matcher.find()) {
                int count = matcher.groupCount();
                if (count == 2) {
                    links.put(matcher.group(2), matcher.group(1));
                }
            }
        }
    }

    public boolean isSuccessful() {
        return code >= 200 && code < 300;
    }

    public Integer getNextPage() {
        String next = links.get(NEXT_LINK);
        if (next == null) {
            return null;
        }
        Matcher matcher = PAGE_PATTERN.matcher(next);
        if (!matcher.find() || matcher.groupCount() != 1) {
            return null;
        }
        try {
            return Integer.parseInt(matcher.group(1));
        } catch (NumberFormatException ex) {
            Timber.w("cannot parse next page from %s", next);
            return null;
        }
    }
}

LiveDataCallAdapter.kt

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


import android.arch.lifecycle.LiveData
import com.bitfurther.notigo.student.api.ApiResponse
import retrofit2.Call
import retrofit2.CallAdapter
import retrofit2.Callback
import retrofit2.Response
import java.lang.reflect.Type
import java.util.concurrent.atomic.AtomicBoolean

/**
 * A Retrofit adapter that converts the Call into a LiveData of ApiResponse.
 * @param <R>
 */
class LiveDataCallAdapter<R>(private val responseType: Type) : CallAdapter<R, LiveData<ApiResponse<R>>> {

    override fun responseType(): Type {
        return responseType
    }

    override fun adapt(call: Call<R>): LiveData<ApiResponse<R>> {
        return object : LiveData<ApiResponse<R>>() {
            internal var started = AtomicBoolean(false)

            override fun onActive() {
                super.onActive()
                if (started.compareAndSet(false, true)) {
                    call.enqueue(object : Callback<R> {
                        override fun onResponse(call: Call<R>, response: Response<R>) {
                            postValue(ApiResponse(response))
                        }

                        override fun onFailure(call: Call<R>, throwable: Throwable) {
                            postValue(ApiResponse(throwable))
                        }
                    })
                }
            }
        }
    }
}

LiveDataCallAdapterFactory.java

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


import android.arch.lifecycle.LiveData;
import android.support.annotation.NonNull;

import com.bitfurther.notigo.student.api.ApiResponse;

import java.lang.annotation.Annotation;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

import retrofit2.CallAdapter;
import retrofit2.Retrofit;

public class LiveDataCallAdapterFactory extends CallAdapter.Factory {

    @Override
    public CallAdapter<?, ?> get(@NonNull Type returnType, @NonNull Annotation[] annotations, @NonNull Retrofit retrofit) {
        if (getRawType(returnType) != LiveData.class) {
            return null;
        }
        Type observableType = getParameterUpperBound(0, (ParameterizedType) returnType);
        Class<?> rawObservableType = getRawType(observableType);
        if (rawObservableType != ApiResponse.class) {
            throw new IllegalArgumentException("type must be a resource");
        }
        if (!(observableType instanceof ParameterizedType)) {
            throw new IllegalArgumentException("resource must be parameterized");
        }
        Type bodyType = getParameterUpperBound(0, (ParameterizedType) observableType);
        return new LiveDataCallAdapter<>(bodyType);
    }
}

"Traditional way"
is there modern way?. Btw thanks for share

Really helpful gist. I noticed that there's no LiveDataCallAdapter.java file (only kotlin) here, so I added it here. Kindly update, thanks!

Thank you for putting this together! I updated the README.md for Usage so the LiveDataCallAdapterFactory is instantiated with the new keyword as below:

Usage

Set the LiveDataCallAdapterFactory in the Retrofit Builder

Retrofit.Builder()
        .baseUrl(BASE_URL)
        // ....
        .addCallAdapterFactory(new LiveDataCallAdapterFactory())
        // ....
        .build()

Can you point me to some tutorial which might help us understand this?

@saravinfotech Here's a series of article which I wrote about LiveData. This should get you started
https://android.jlelse.eu/exploring-livedata-architecture-component-f9375d3644ee

Let me know if you need anything else