Android JsonDeserializer在返回響應時出錯

Question

即時消息在這裏，我有一個問題，我無法解決。

即時得到這個錯誤在調試中執行時間：

05-02 11:56:07.539 18645-24466/com.appss.appssapp D/Retrofit﹕ java.lang.NullPointerException: Null pointer exception during instruction 'invoke-static {v0, v2}, java.util.ArrayList com.appss.appssapp.io.model.PostsResponse$MainResponse.access$002(com.appss.appssapp.io.model.PostsResponse$MainResponse, java.util.ArrayList) // method@19256' 
at com.appss.appssapp.io.model.PostsResponse.setPosts(PostsResponse.java:21) 
      at com.appss.appssapp.io.deserializer.PostsResponseDeserializer.deserialize(PostsResponseDeserializer.java:31) 
      at com.appss.appssapp.io.deserializer.PostsResponseDeserializer.deserialize(PostsResponseDeserializer.java:21) 
      at com.google.gson.TreeTypeAdapter.read(TreeTypeAdapter.java:58) 
      at com.google.gson.Gson.fromJson(Gson.java:810) 
      at com.google.gson.Gson.fromJson(Gson.java:775) 
      at retrofit.converter.GsonConverter.fromBody(GsonConverter.java:63) 
      at retrofit.RestAdapter$RestHandler.invokeRequest(RestAdapter.java:367) 
      at retrofit.RestAdapter$RestHandler.access$100(RestAdapter.java:220) 
      at retrofit.RestAdapter$RestHandler$2.obtainResponse(RestAdapter.java:278) 
      at retrofit.CallbackRunnable.run(CallbackRunnable.java:42) 
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
      at retrofit.Platform$Android$2$1.run(Platform.java:142) 
      at java.lang.Thread.run(Thread.java:818) 

應用程序被編譯正確，沒有問題，運行，但是當我向API調用不顯示數據，我意思是，api發送數據，我做了我必須做的事情，但是當我嘗試發送de數據到調試中的響應時，顯示出我上面寫到的問題。

這是我的代碼。

Posts.JAVA

public class Posts { 
    String id; //Id de la publicacion 
    String titulo; // Titulo de la publicacion 
    String url; // Url de la publicacion 
    String imagen; // Imagen cover la publicacion 
    String autor_nick; // Nick del autor de la publicacion 
    String visitas; // Lecturas de la publicacion 
    String comentarios; // Cantidad de comentarios de la publicacion 
    public Posts() {} 
    public String getId() { 
     return id; 
    } 
    public void setId(String id) { 
     this.id = id; 
    } 
    public String getTitulo() { 
     return titulo; 
    } 
    public void setTitulo(String titulo) { 
     this.titulo = titulo; 
    } 
    public String getUrl() { 
     return url; 
    } 
    public void setUrl(String url) { 
     this.url = url; 
    } 
    public String getImagen() { 
     return imagen; 
    } 
    public void setImagen(String imagen) { 
     this.imagen = imagen; 
    } 
    public String getAutor_nick() { 
     return autor_nick; 
    } 
    public void setAutor_nick(String autor_nick) { 
     this.autor_nick = autor_nick; 
    } 
    public String getVisitas() { 
     return visitas; 
    } 
    public void setVisitas(String visitas) { 
     this.visitas = visitas; 
    } 
    public String getComentarios() { 
     return comentarios; 
    } 
    public void setComentarios(String comentarios) { 
     this.comentarios = comentarios; 
    } 
} 

PostsResponse.JAVA

public class PostsResponse { 

    private MainResponse mainResponse; 

    public ArrayList<Posts> getPosts(){ 
     return mainResponse.posts; 
    } 

    public void setPosts(ArrayList<Posts> posts) { 
     mainResponse.posts = posts; 
    } 

    private class MainResponse { 

     private ArrayList<Posts> posts; 

    } 
} 

PostResponseDeserializer.JAVA

public class PostsResponseDeserializer implements JsonDeserializer<PostsResponse> { 
    @Override 
    public PostsResponse deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { 
     Gson gson = new Gson(); 
     PostsResponse response = gson.fromJson(json, PostsResponse.class); 

     JsonObject postsResponseData = json.getAsJsonObject(); 

     JsonArray postsArray = postsResponseData.getAsJsonArray("posts"); 

     response.setPosts(extractPostsFromJsonArray(postsArray)); 

     return response; 
    } 

    private ArrayList<Posts> extractPostsFromJsonArray(JsonArray postsArray) { 
     ArrayList<Posts> posts = new ArrayList<>(); 
     for (int i = 0; i < postsArray.size(); i++) { 

      JsonObject postsDatos = postsArray.get(i).getAsJsonObject(); 

      Posts actualPost = new Posts(); 
      String titulo = postsDatos.get("titulo").getAsString(); 
      String imagen = postsDatos.get("imagen_370x208").getAsString(); 
      String visitas = postsDatos.get("visitas").getAsString(); 

      actualPost.setTitulo(titulo); 
      actualPost.setImagen(imagen); 
      actualPost.setVisitas(visitas); 

      posts.add(actualPost); 
     } 
     return posts; 
    } 
} 

我認爲問題可能在這裏 response.setPosts（extractPostsFromJsonArray（postsArray））;

但我不明白爲什麼會發生這種情況。

任何幫助？ ..對我的壞英語感到抱歉。

Answer 1

我不確定，但檢查這一點。

當您調用setposts方法時，它將嘗試初始化一個ArrayList，而包含該列表的對象未初始化。所以你應該首先新建一個MainResponse的實例。