Android @Inject不是初始化字段
我第一次学习Dragger 2,面临的问题是我的课程代码Android @Inject不是初始化字段,android,dependency-injection,Android,Dependency Injection,我第一次学习Dragger 2,面临的问题是我的课程代码 public class User { private String firstName; private String lastName; public User(String firstName, String lastName) { this.firstName = firstName; this.lastName = las
public class User {
private String firstName;
private String lastName;
public User(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
@Override
public String toString() {
return "User [firstName=" + firstName + ", lastName=" + lastName + "]";
}
}
以及具有用户依赖关系的BackendService类
public class BackendService {
@Inject
public User user;
private String serverUrl;
@Inject
public BackendService(@Named("serverUrl") String serverUrl) {
this.serverUrl = serverUrl;
}
public boolean callServer() {
if (user !=null && serverUrl!=null && serverUrl.length()>0) {
System.out.println("User: " + user + " ServerUrl: " + serverUrl);
return true;
}
return false;
}
}
和后端服务模块
@Module
public class BackEndServiceModule {
@Provides
@Singleton
BackendService provideBackendService(@Named("serverUrl") String serverUrl) {
return new BackendService(serverUrl);
}
@Provides
@Singleton
@Named("serverUrl")
String provideServerUrl() {
return "http://www.vogella.com";
}
@Provides
@Singleton
@Named("anotherUrl")
String provideAnotherUrl() {
return "http://www.google.com";
}
}
和用户模块
@Module
public class UserModule {
@Provides
@Singleton
User providesUser() {
return new User("James","Peter");
}
}
以及MyComponent
@Singleton
@Component(modules = { UserModule.class, BackEndServiceModule.class})
public interface MyComponent {
void inject(TestClass activity);
}
我的测试类代码是
public class TestClass {
@Inject
BackendService backendService; //
private MyComponent component;
public TestClass(){
component = DaggerMyComponent.builder().build();
component.inject(this);
callServer();
}
private void callServer() {
boolean callServer = backendService.callServer();
if (callServer) {
Log.v("TestClass","Server call was successful."+backendService.user);
} else {
Log.v("TestClass","Server call failed."+backendService.user);
}
}
} // this is alway null backendService.user
问题是BackendService中的用户字段始终为空。请指出我的问题所在。在
BackenService
构造函数中添加用户
参数,并从用户
变量中删除@Inject
注释
public User user
@Inject
public BackendService(@Named("serverUrl") String serverUrl,User user) {
this.serverUrl = serverUrl;
this.user=user
}
并删除BackendService提供程序方法
Remove this
@Provides
@Singleton
BackendService provideBackendService(@Named("serverUrl") String serverUrl) {
return new BackendService(serverUrl);
}