[英]Simplifying triple nested loop to avoid callback hell in android retrofit2 (via RxJava2?)
使用android retrofit2,需要访问深层嵌套的name
字符串以获取并显示其Details
(其中Detail
的对象引用了用于获取Detail
的Group
和User
对象)。
JSON
由一个Group
列表组成,每个Group
包含一个User
列表,每个User
包含一个name
String
列表,这些name
在以下模型中捕获:
public class Group {
@SerializedName("id")
public String id;
@SerializedName("users")
public List<User> users;
}
public class User {
@SerializedName("id")
public String id;
@SerializedName("detailNames")
public List<String> detailNames;
}
public class Detail {
// allow access to objects used to get detail
public Group group;
public User user;
@SerializedName("name")
public String name;
@SerializedName("description")
public String description;
}
使用UserApi
填充模型:
public interface UserApi {
@GET("groups")
Call<List<Group>> getGroups();
@GET("groups/{group_id}/users/{user_id}/details/{detail_name}")
Call<Detail> getDetail(
@Path("group_id") String groupId,
@Path("user_id") String userId,
@Path("detail_name") String detailName
);
}
目的是使用给定的UserApi
发出和解析请求以显示以下格式的Dialog
:
Group1 (expandable heading)
User1 (expandable heading)
Detail1 (checkbox)
Detail2 (checkbox)
...
Group2 (expandable heading)
User2 (expandable heading)
Detail1 (checkbox)
...
...
...
问题是当前解决方案请求Group
并使用三重嵌套的for
循环访问和获取每个name
Detail
:
private void fetchDetails(List<Group> groupList) {
ArrayList<Group> groups = (ArrayList<Group>) groupList;
if (groups != null && groups.size() > 0) {
for (Group group : groups) {
for (User user: group.users) {
for (String detailName : user.detailNames) {
fetchDetail(group, user, detailName);
}
}
}
}
}
由于三重循环为每个name
发出请求,并且在getGroups
onResponse
回调中完成,因此问题变得更加严重,这似乎onResponse
/无法维护:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mUserApi = UserApiClient.getApi();
fetchGroups();
}
private void fetchGroups() {
Callback<List<Group>> groupsCall = new Callback<List<Group>>() {
@Override
public void onResponse(Call<List<Group>> call, Response<List<Group>> response) {
int statusCode = response.code();
switch (statusCode) {
case HttpURLConnection.HTTP_OK:
List<Group> groups = response.body();
fetchDetails(groups);
break;
}
}
@Override
public void onFailure(Call<List<Group>> call, Throwable t) {}
};
mUserApi.getGroups().enqueue(groupsCall);
}
private void fetchDetail(final Group group, final User user, String detailName) {
Callback<Detail> detailCallback= new Callback<Detail>() {
@Override
public void onResponse(Call<Detail> call, Response<Detail> response) {
int statusCode = response.code();
switch (statusCode) {
case HttpURLConnection.HTTP_OK:
MainActivity.this.runOnUiThread(new Runnable() {
@Override
public void run() {
// display details in ListView
}
});
break;
}
}
@Override
public void onFailure(Call<Detail> call, Throwable t) {}
};
mUserApi.getDetail(group.id, user.id, detailName).enqueue(detailCallback);
}
建议使用RxJava2解决方案来避免像上述实现那样嵌套回调,但由于在管理3层嵌套访问names
方面存在困惑,因此未完成:
Observable<List<Group>> groupCall = mUserApi.getGroups();
groupCall.flatMapIterable(x -> x)
.flatMap(group -> {
Observable.fromIterable(group.users)
.flatMap(user -> {
Observable.fromIterable(user.detailNames)
.map(detailName -> {
mUserApi.getDetail(group.id, user.id, detailName)
.flatMap(detail -> {
detail.group = group;
detail.user = user;
return Observable.just(detail)
})
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Observer<List<Group>>() {
@Override
public void onSubscribe(Disposable d) {}
@Override
public void onNext(List<Detail> value) {
mDetails = (ArrayList<Detail>) value;
}
@Override
public void onError(Throwable e) {}
@Override
public void onComplete() {}
});
});
}
})
存在一些问题(例如, 带有条件的RxJava多循环 )可以处理RxJava中的嵌套,但仍不确定如何将其应用于深度嵌套的name
s。
是否可以使用RxJava2避免回调地狱并简化三重for
循环,还有其他方法,还是该解决方案应诉诸AsyncTask
/ AsyncTaskLoader
同步请求?
正如我在评论中提到的那样,我认为您已经拥有的几乎是最简单的表格。 但是似乎您有兴趣在没有循环的情况下执行此操作,因此这里有一些建议(但不一定更好):
方法1:容器类
如果您愿意创建可以在单个对象中容纳组,用户,详细信息名称的中间容器类,则可以执行以下操作:
首先,创建以下容器类:
public class UserWithGroup {
final Group group;
final User user;
public UserWithGroup(Group group, User user) {
this.group = group;
this.user = user;
}
}
public class DetailWithUser {
final Group group;
final User user;
final String detailName;
public DetailWithUser(Group group, User user, String detailName) {
this.group = group;
this.user = user;
this.detailName = detailName;
}
}
然后,使用Java 8 Stream的代码可以是:
private void fetchDetails(List<Group> groupList) {
groupList.stream()
.flatMap(g -> g.users.stream().map(u -> new UserWithGroup(g, u)))
.flatMap(ug -> ug.user.detailNames.stream().map(n -> new DetailWithUser(ug.group, ug.user, n)))
.forEach(d -> fetchDetail(d.group, d.user, d.detailName));
}
或使用RxJava:
private void fetchDetails2(List<Group> groupList) {
Observable.fromIterable(groupList)
.flatMap(g -> Observable.fromIterable(g.users).map(u -> new UserWithGroup(g, u)))
.flatMap(ug -> Observable.fromIterable(ug.user.detailNames).map(n -> new DetailWithUser(ug.group, ug.user, n)))
.flatMap(d -> mUserApi.getDetail(d.group.id, d.user.id, d.detailName)
.map(detail -> {
detail.group = d.group;
detail.user = d.user;
return detail
}))
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(detail -> {
...
});
}
方法2:
Android.util.Pair
一个可以容纳任何两个对象的容器类。 如果使用此方法而不是创建中间容器,并且可以使用,则可以进一步简化代码。
Java 8流和配对:
private void fetchDetails3(List<Group> groupList) {
groupList.stream()
.flatMap(g -> g.users.stream().map(u -> Pair.create(g, u)))
.flatMap(p -> p.second.detailNames.stream().map(n -> Pair.create(p, n)))
.forEach(p -> fetchDetail(p.first.first, p.first.second, p.second));
}
RxJava和配对:
private void fetchDetails4(List<Group> groupList) {
Observable.fromIterable(groupList)
.flatMap(g -> Observable.fromIterable(g.users).map(u -> Pair.create(g, u)))
.flatMap(p -> Observable.fromIterable(p.second.detailNames).map(n -> Pair.create(p, n)))
.flatMap(p -> fetchDetail2(p.first.first, p.first.second, p.second)
.map(detail -> {
detail.group = d.group;
detail.user = d.user;
return detail
}))
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(detail -> {
...
});
}
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