libGDX json錯誤

Question

我想保存項目的Arraylist並保存並加載它。 這是我要加載的ArrayList：

public static ArrayList<Item> inventory = new ArrayList<Item>(); 
public mainscreen(final luckyllama gam) { 
     game = gam; 
     json = new Json(); 
     json.setIgnoreUnknownFields(true); 
       if( json.fromJson(ArrayList.class, 
       Gdx.files.internal("data/inventory.json")) != null){ 
        ArrayList<JsonValue> list = json.fromJson(ArrayList.class, 
          Gdx.files.internal("data/inventory.json")); 
        for (JsonValue v : list) { 
         inventory.add(json.readValue(Item.class, v)); 
        } 
       } 
... 

我這是怎麼保存的ArrayList：

mainscreen.json.toJson(mainscreen.inventory, Gdx.files.local("data/inventory.json")); 

這是Item類的一部分：

public class Item { 
    public float x, y, speedx, speedy; 
    public Rectangle container, icontainer; 
    public Sprite texture; 
    public int Quality; 
    static int amount; 
    static int spawned; 
    public int itemtype; 
    static Item item; 

這是我保存文件後的json文件：

[{ 
    class: com.algrande.luckyllama.Item, 
    y: 50, 
    speedx: -2.5, 
    container: { 
     y: 50, 
     width: 50, 
     height: 30 
    }, 
    texture: { 
     texture: { 
      glTarget: 3553, 
      glHandle: 1, 
      minFilter: Linear, 
      magFilter: Linear, 
      uWrap: ClampToEdge, 
      vWrap: ClampToEdge, 
      data: { 
       class: com.badlogic.gdx.graphics.glutils.FileTextureData, 
       file: { 
        class: com.badlogic.gdx.backends.lwjgl.LwjglFileHandle, 
        file: { 
         path: items\\items.png 
        }, 
        type: Internal 
       }, 
       width: 4096, 
       height: 4096, 
       format: RGBA8888, 
       pixmap: null, 
       useMipMaps: false, 
       isPrepared: false 
      } 
     }, 
     u: 0.25, 
     u2: 0.5, 
     v2: 0.25, 
     regionWidth: 1024, 
     regionHeight: 1024, 
     vertices: [0, 
     0, 
     -1.7014117E38, 
     0.25, 
     0.25, 
     0, 
     0, 
     -1.7014117E38, 
     0.25, 
     0, 
     0, 
     0, 
     -1.7014117E38, 
     0.5, 
     0, 
     0, 
     0, 
     -1.7014117E38, 
     0.5, 
     0.25], 
     width: 1024, 
     height: 1024, 
     originX: 512, 
     originY: 512 
    }, 
    Quality: 1, 
    itemtype: 62 
}] 

但我發現了這個錯誤：

Exception in thread "LWJGL Application" com.badlogic.gdx.utils.SerializationException: Error reading file: data/inventory.json 
     at com.badlogic.gdx.utils.Json.fromJson(Json.java:694) 
     at com.algrande.luckyllama.screens.mainscreen.<init>(mainscreen.java:78) 
     at com.algrande.luckyllama.luckyllama.create(luckyllama.java:19) 
     at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:147) 
     at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:124) 
    Caused by: com.badlogic.gdx.utils.SerializationException: Class cannot be created (missing no-arg constructor): com.badlogic.gdx.graphics.Texture 
    Serialization trace: 
    texture (com.badlogic.gdx.graphics.g2d.Sprite) 
    texture (com.algrande.luckyllama.Item) 
     at com.badlogic.gdx.utils.Json.newInstance(Json.java:1042) 
     at com.badlogic.gdx.utils.Json.readValue(Json.java:892) 
     at com.badlogic.gdx.utils.Json.readFields(Json.java:797) 
     at com.badlogic.gdx.utils.Json.readValue(Json.java:919) 
     at com.badlogic.gdx.utils.Json.readFields(Json.java:797) 
     at com.badlogic.gdx.utils.Json.readValue(Json.java:919) 
     at com.badlogic.gdx.utils.Json.readValue(Json.java:947) 
     at com.badlogic.gdx.utils.Json.fromJson(Json.java:692) 
     ... 4 more 
    Caused by: com.badlogic.gdx.utils.reflect.ReflectionException: Could not instantiate instance of class: com.badlogic.gdx.graphics.Texture 
     at com.badlogic.gdx.utils.reflect.ClassReflection.newInstance(ClassReflection.java:70) 
     at com.badlogic.gdx.utils.Json.newInstance(Json.java:1024) 
     ... 11 more 
    Caused by: java.lang.InstantiationException: com.badlogic.gdx.graphics.Texture 
     at java.lang.Class.newInstance(Class.java:427) 
     at com.badlogic.gdx.utils.reflect.ClassReflection.newInstance(ClassReflection.java:68) 
     ... 12 more 
    Caused by: java.lang.NoSuchMethodException: com.badlogic.gdx.graphics.Texture.<init>() 
     at java.lang.Class.getConstructor0(Class.java:3082) 
     at java.lang.Class.newInstance(Class.java:412) 
     ... 13 more 

什麼我做錯了，我該如何解決？

Answer 1

Json的自動反序列化依賴於空的構造函數來實例化每個對象。 Json只能使用它們的空構造函數反序列化類。由於Item引用了一個Sprite，它引用了一個Texture;並且由於Texture沒有任何空構造函數，所以不能自動反序列化Item。

所以你的選擇是

1）在保存前設置精靈參考爲空。然後切換回來。

2）刪除Item類中Sprite的引用。相反，將一個TextureRegion傳遞給Item的render方法（如果它有一個）。

3）使用定製的Json串行器。您可以將一個序列化程序分配給Sprite，它不會讀取或寫入任何內容。例如讀取或您的JSON實例寫之前：

json.setSerializer(Sprite.class, new ReadOnlySerializer<Sprite>() { 
    public Sprite read (Json json, JsonValue jsonData, Class type) { 
     return (Sprite)null; 
    } 
} 

那麼你的項目類需要它的加載後，分配給它，也許這樣的精靈：

public class Item { 
    //... 
    private String spriteName; 

    //... 

    /**Call this on every Item immediately after it has been loaded from Json. */ 
    public void onLoadedFromJson (TextureAtlas atlas){ 
     texture = atlas.createSprite(spriteName); 
     sprite.setPosition(x, y); 
    } 
}