我想在我的android应用程序中获取工作线索列表。我使用Dagger 2和Retrofit和OkHttp，但我收到此错误
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.../com...AccueilActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object retrofit2.Retrofit.create(java.lang.Class)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3319)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
at android.app.ActivityThread.access$1100(ActivityThread.java:229)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:7325)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object retrofit2.Retrofit.create(java.lang.Class)' on a null object reference
我创建两个组件ApplicationComponent，NetComponent
@Singleton
@Component(modules = {NetModule.class,ApplicationModule.class})
public interface NetComponent {
void inject(AppCompatActivity activity);
void inject(Fragment fragment);
}
和Tow模块ApplicationModule，NetModule
import android.app.Application;
import dagger.Module;
import dagger.Provides;
import okhttp3.Cache;
import okhttp3.OkHttpClient;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
import com.google.gson.FieldNamingPolicy;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import javax.inject.Singleton;
@Module
public class NetModule {
String baseUrl;
public NetModule(String baseUrl) {
this.baseUrl = baseUrl;
}
@Provides
@Singleton
Cache provideOkHttpCache(Application application) {
int cacheSize = 10 * 1024 * 1024; // 10 MiB
Cache cache = new Cache(application.getCacheDir(), cacheSize);
return cache;
}
@Provides
@Singleton
Gson provideGson() {
GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES);
return gsonBuilder.create();
}
@Provides
@Singleton
OkHttpClient provideOkHttpClient(Cache cache) {
OkHttpClient client = new OkHttpClient.Builder().cache(cache).build();
return client;
}
@Provides
@Singleton
public Retrofit provideRetrofit(Gson gson, OkHttpClient okHttpClient) {
Retrofit retrofit = new Retrofit.Builder()
.addConverterFactory(GsonConverterFactory.create(gson))
.baseUrl(baseUrl)
.client(okHttpClient)
.build();
return retrofit;
}
}
我尝试在我的Activity中注入Retrofit，但我得到null异常
public class AccueilActivity extends AppCompatActivity {
ArrayList<MenuItem> menu = new ArrayList<>();
@Inject
Retrofit retrofit;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_accueil);
((AndroidApplication) getApplicationContext()).getNetComponent().inject(this);
Call<List<JobLeads>> jobLeadList = retrofit.create(GetJobLeads.class).getJobLeads();
jobLeadList.enqueue(new Callback<List<JobLeads>>() {
@Override
public void success(Result<List<JobLeads>> result) {
}
@Override
public void failure(TwitterException exception) {
}
});
}
这是AndroidApplication类
public class AndroidApplication extends Application {
private ApplicationComponent applicationComponent;
private NetComponent netComponent;
@Override
public void onCreate() {
super.onCreate();
this.initializeInjector();
SugarContext.init(this);
}
private void initializeInjector() {
this.applicationComponent = DaggerApplicationComponent.builder()
.applicationModule(new ApplicationModule(this))
.build();
this.netComponent = DaggerNetComponent.builder()
.applicationModule(new ApplicationModule(this))
.netModule(new NetModule(JOB_LEADS_API2))
.build();
}
public ApplicationComponent getApplicationComponent() {
return this.applicationComponent;
}
public NetComponent getNetComponent() {
return this.netComponent;
}
@Override
public void onTerminate() {
super.onTerminate();
SugarContext.terminate();
}
}
答案 0 :(得分：1)
你应该注入AccueilActivity而不是AppCompatActivity
@Singleton
@Component(modules = {NetModule.class,ApplicationModule.class})
public interface NetComponent {
void inject(AccueilActivity activity);
void inject(Fragment fragment);
}
编辑：这是我的工作示例：
创建一个InjectHelper，以便在其他类中重用
public class InjectHelper {
private static RootComponent sRootComponent;
static {
initModules();
}
private static void initModules() {
sRootComponent = getRootComponentBuilder().build();
}
public static DaggerRootComponent.Builder getRootComponentBuilder() {
return DaggerRootComponent.builder();
}
public static RootComponent getRootComponent() {
if (sRootComponent == null) {
initModules();
}
return sRootComponent;
}
}
组件
@Singleton
@Component(modules = { NetModule.class })
public interface RootComponent {
void inject(AccueilActivity activity);
void inject(Fragment fragment);
}
具有改造实例的网络模块
@Module
public class NetModule {
private static final int CONNECT_TIMEOUT = 45;
private static final int WRITE_TIMEOUT = 45;
private static final int READ_TIMEOUT = 45;
private static final long CACHE_SIZE = 10 * 1024 * 1024; // 10 MB
private Cache provideHttpCache() {
return new Cache(App.getInstance().getCacheDir(), CACHE_SIZE);
}
/**
* @return OkHttpClient.Builder an instance of the configured http client
*/
private OkHttpClient provideOkHttpClient() {
OkHttpClient.Builder client = new OkHttpClient.Builder();
client.connectTimeout(CONNECT_TIMEOUT, TimeUnit.SECONDS);
client.readTimeout(READ_TIMEOUT, TimeUnit.SECONDS);
client.writeTimeout(WRITE_TIMEOUT, TimeUnit.SECONDS);
client.cache(provideHttpCache());
client.addInterceptor(new Interceptor() {
@Override
public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
if (isConnected(App.getContext())) {
request = request.newBuilder().header("Cache-Control", "public, max-age=" + 60).build();
} else {
request = request.newBuilder().header("Cache-Control", "public, only-if-cached, max-stale=" + 60 * 60 * 24 * 7).build(); // 1 week
}
return chain.proceed(request);
}
});
return client.build();
}
private Gson provideGsonParser(){
return new GsonBuilder()
.setDateFormat("dd-MM-yyyy 'at' HH:mm")
.create();
}
/**
* Provides a singleton instance of Retrofit. This is injected with dagger DI into the baseDAO
* @return Retrofit instance to create the api calls
*/
@Provides
@Singleton
public Retrofit provideRetrofit() {
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(App.getContext().getString(R.string.base_url))
.client(provideOkHttpClient())
.addConverterFactory(GsonConverterFactory.create(provideGsonParser()))
.build();
return retrofit;
}
private boolean isConnected(Context context) {
ConnectivityManager cm = (ConnectivityManager) context
.getSystemService(Context.CONNECTIVITY_SERVICE);
if (cm == null) {
return false;
}
NetworkInfo info = cm.getActiveNetworkInfo();
return info != null && info.isConnected();
}
}
在您的活动中注入：
public class MainActivity extends AppCompatActivity {
@Inject
Retrofit retrofit;
private ApiService service;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
InjectHelper.getRootComponent().inject(this); // call the InjectHelper
service = retrofit.create(ApiService.class); // use retrofit
}