如何使用嵌套對象創建類Parcelable

Question

我想創建A類Parcelable類。

public class A { 
    public String str; 
    public ArrayList<B> list; 
} 

這是我想出這麼遠。但是它會因NullPointerException而崩潰。問題是這兩個陳述：dest.writeList(list); & in.readList(list, this.getClass().getClassLoader());。 我想不出什麼從這裏做:(

A類

public class A implements Parcelable { 
    public String str; 
    public ArrayList<B> list; 

    @Override 
    public int describeContents() { 
     // TODO Auto-generated method stub 
     return 0; 
    } 

    @Override 
    public void writeToParcel(Parcel dest, int flags) { 
     dest.writeString(str); 
     dest.writeList(list); 
    } 

    private A(Parcel in) { 
     str = in.readString(); 
     in.readList(list, this.getClass().getClassLoader()); 
    } 

    public static final Parcelable.Creator<A> CREATOR 
      = new Parcelable.Creator<A>() { 
     public A createFromParcel(Parcel in) { 
      return new A(in); 
     } 

     public A[] newArray(int size) { 
      return new A[size]; 
     } 
    }; 
} 

B類

public class B implements Parcelable { 
    public String str; 

    @Override 
    public int describeContents() { 
     // TODO Auto-generated method stub 
     return 0; 
    } 

    @Override 
    public void writeToParcel(Parcel dest, int flags) { 
     dest.writeString(str); 
    } 

    private B(Parcel in) { 
     str = in.readString(); 
    } 

    public static final Parcelable.Creator<B> CREATOR 
      = new Parcelable.Creator<B>() { 
     public B createFromParcel(Parcel in) { 
      return new B(in); 
     } 

     public B[] newArray(int size) { 
      return new B[size]; 
     } 
    }; 
} 

謝謝您的時間。

Answer 1

我終於想出了要輸入Google的內容:)，並發現這個Android, How to use readTypedList method correctly in a Parcelable class?

解決方案是使用read-/writeTypedList來代替。我還初始化arraylist以避免任何進一步的NullPointerException。

A類

public class A implements Parcelable { 
    public String str; 
    public ArrayList<B> list = new ArrayList<B>(); 

    @Override 
    public int describeContents() { 
     // TODO Auto-generated method stub 
     return 0; 
    } 

    @Override 
    public void writeToParcel(Parcel dest, int flags) { 
     dest.writeString(str); 
     dest.writeTypedList(list); 
    } 

    private A(Parcel in) { 
     str = in.readString(); 
     in.readTypedList(list, B.CREATOR); 
    } 

    public static final Parcelable.Creator<A> CREATOR 
      = new Parcelable.Creator<A>() { 
     public A createFromParcel(Parcel in) { 
      return new A(in); 
     } 

     public A[] newArray(int size) { 
      return new A[size]; 
     } 
    }; 
} 

B類

public class B implements Parcelable { 
    public String str; 

    @Override 
    public int describeContents() { 
     // TODO Auto-generated method stub 
     return 0; 
    } 

    @Override 
    public void writeToParcel(Parcel dest, int flags) { 
     dest.writeString(str); 
    } 

    private B(Parcel in) { 
     str = in.readString(); 
    } 

    public static final Parcelable.Creator<B> CREATOR 
      = new Parcelable.Creator<B>() { 
     public B createFromParcel(Parcel in) { 
      return new B(in); 
     } 

     public B[] newArray(int size) { 
      return new B[size]; 
     } 
    }; 
} 

Answer 2

如果你有你的主要Parcelable對象內部只有一個Parcelable對象，沒有列出像接受的答案的情況。然後，它會像下面這樣：

A類

public class A implements Parcelable { 
    public String str; 
    public B objectB; 

    @Override 
    public int describeContents() { 
     // TODO Auto-generated method stub 
     return 0; 
    } 

    @Override 
    public void writeToParcel(Parcel dest, int flags) { 
     //The parcelable object has to be the first one 
     dest.writeParcelable(objectB, flags); 
     dest.writeString(str); 
    } 

    private A(Parcel in) { 
     this.objectB = in.readParcelable(B.class.getClassLoader()); 
     str = in.readString(); 
    } 

    public static final Parcelable.Creator<A> CREATOR 
      = new Parcelable.Creator<A>() { 
     public A createFromParcel(Parcel in) { 
      return new A(in); 
     } 

     public A[] newArray(int size) { 
      return new A[size]; 
     } 
    }; 
} 

B類

public class B implements Parcelable { 
    public String str; 

    @Override 
    public int describeContents() { 
     // TODO Auto-generated method stub 
     return 0; 
    } 

    @Override 
    public void writeToParcel(Parcel dest, int flags) { 
     dest.writeString(str); 
    } 

    private B(Parcel in) { 
     str = in.readString(); 
    } 

    public static final Parcelable.Creator<B> CREATOR 
      = new Parcelable.Creator<B>() { 
     public B createFromParcel(Parcel in) { 
      return new B(in); 
     } 

     public B[] newArray(int size) { 
      return new B[size]; 
     } 
    }; 
} 

重要： 請注意，如果您寫入和讀取順序Parcelable對象事項。結帳這個answer瞭解更多詳情

Answer 3

只要按下ALT + ENTER並更換Parcelable將實施所有必要的實施

Answer 4

您可以從首選項添加Parcelable代碼生成器插件，從那裏你可以創建parcelable鍋爐板代碼這樣做： - 右鍵點擊模型 內的類名稱 - 選擇產生 - 選擇Parcelable

似的 - 你的模型將需要Parcelable樣板代碼進行更新。

Answer 5

我在這裏同樣的問題，是一個generic version

class Item<T : Parcelable> (val model: T, val index: Int) : Parcelable { 

    constructor(parcel: Parcel) : 
     this(parcel.readParcelable(
      Item<T>::model.javaClass.classLoader), 
      parcel.readInt() 
     ) {} 

    override fun writeToParcel(parcel: Parcel?, flag: Int) { 
     parcel?.writeParcelable(model, 0) 
     parcel?.writeInt(index) 
    } 

    override fun describeContents(): Int { 
     return 0 
    } 

    companion object CREATOR : Parcelable.Creator<Item<Parcelable>> { 
     override fun createFromParcel(parcel: Parcel): Item<Parcelable> { 
      return Item(parcel) 
     } 

     override fun newArray(size: Int): Array<Item<Parcelable>?> { 
      return arrayOfNulls(size) 
     } 
    } 
}