java - 资源类和 null 参数

Question

我有一个可变的实时数据:

private MutableLiveData<Resource<LoginResponse>> loginRequestData = new MutableLiveData<>();

我正在使用 Google 提供的资源类:

public class Resource<T> {

    @NonNull
    public final Status status;

    @Nullable
    public final T data;

    @Nullable
    public final String message;

    public Resource(@NonNull Status status, @Nullable T data, @Nullable String message) {
        this.status = status;
        this.data = data;
        this.message = message;
    }

    public static <T> Resource<T> success(@NonNull T data) {
        return new Resource<>(Status.SUCCESS, data, null);
    }

    public static <T> Resource<T> error(@NonNull String msg, @Nullable T data) {
        return new Resource<>(Status.ERROR, data, msg);
    }

    public static <T> Resource<T> loading(@Nullable T data) {
        return new Resource<>(Status.LOADING, data, null);
    }

    public enum Status { SUCCESS, ERROR, LOADING}
}

我的LoginResponse类:

public class LoginResponse {

    @SerializedName("status")
    @Expose
    private int status;

    @SerializedName("key")
    @Expose
    private String key;

    @SerializedName("anonid")
    @Expose
    private String anonid;

    @SerializedName("username")
    @Expose
    private String username;

    @SerializedName("photo")
    @Expose
    private String photo;

    @SerializedName("isBanned")
    @Expose
    private int isBanned;


    public int getStatus() {
        return status;
    }

    public String getKey() {
        return key;
    }

    public String getAnonid() {
        return anonid;
    }

    public String getUsername() {
        return username;
    }

    public String getPhoto() {
        return photo;
    }

    public int getIsBanned() {
        return isBanned;
    }
}

正如您所猜测的，我正在使用此实时数据进行网络请求。在网络请求之前，我想通过以下行将其设置为加载模式:

loginRequestData.setValue(Resource.loading(null));

但是我收到以下编译器错误:

error: no suitable method found for setValue(Resource) method LiveData.setValue(Resource) is not applicable (argument mismatch; Resource cannot be converted to Resource) method MutableLiveData.setValue(Resource) is not applicable (argument mismatch; Resource cannot be converted to Resource)

为什么我无法为 Resource.loading 方法传递 null 参数？

Answer 1

LiveData您定义了期望 Resource<LoginResponse> 的实例，不是 Resource<?> 的实例，这就是您所提供的。试试这个:

loginRequestData.setValue(Resource.<LoginResponse>loading(null));

这样，您就可以确保 null Resource您使用loading加载方法的类型为Resource<LoginResponse> .