如何擴展實現Parcelable接口的android類？

Question

首先我檢查this answer。

我想要做的是擴展Location類叫做LocationPlus，它有一些 成員變量。我試圖實現的功能是將LocationPlus類的對象從一個活動傳遞到另一個活動。

這裏試着寫構造

public LocationPlus(Parcel in) { 

有人在評論問我後LocationPlus上課的時候是我CREATOR

public static final Parcelable.Creator<LocationPlus> CREATOR = new Parcelable.Creator<LocationPlus>() { 
    @Override 
    public LocationPlus createFromParcel(Parcel source) { 
     return new LocationPlus(source); 
    } 
    @Override 
    public LocationPlus[] newArray(int size) { 
     return new LocationPlus[size]; 
    } 
}; 

問題我面臨的是此錯誤

Implicit super constructor Location() is undefined. Must explicitly invoke another constructor 

所以這裏是

public class LocationPlus extends Location{ 

    private int mBattery = -1; 

    public LocationPlus(String locationName) { 
     super(locationName); 
    } 

    public LocationPlus(Location location) { 
     super(location); 
    } 

    public int getmBattery() { 
     return mBattery; 
    } 

    public void setmBattery(int mBattery) { 
     this.mBattery = mBattery; 
    } 
    @Override 
    public int describeContents() { 
     return 0; 
    } 

    public static final Parcelable.Creator<LocationPlus> CREATOR = new Parcelable.Creator<LocationPlus>() { 
     @Override 
     public LocationPlus createFromParcel(Parcel source) { 
      return new LocationPlus(source); 
     } 
     @Override 
     public LocationPlus[] newArray(int size) { 
      return new LocationPlus[size]; 
     } 
    }; 

    @Override 
    public void writeToParcel(Parcel out, int flags) { 
     super.writeToParcel(out, flags); 
     out.writeInt(mBattery); 
    } 

    public LocationPlus(Parcel in) { 
     mBattery =in.readInt(); 
    } 
} 

Answer 1

根據Android文檔，位置類沒有Location()構造函數。在初始化您的LocationPlus班時，您需要撥打super(String provider)或super(Location l)。

編輯：更正語法

（見Location Android Doc）

Answer 2

嘗試這種解決方案：

public static final Parcelable.Creator<LocationPlus> CREATOR = 
    new Parcelable.Creator<LocationPlus>() { 
    @Override 
    public LocationPlus createFromParcel(Parcel in) { 

     Location l = Location.CREATOR.createFromParcel(in); 
     LocationPlus lp = new LocationPlus(l); 

     lp.mBattery= in.readInt(); 

     return lp; 
    } 

    @Override 
    public LocationPlus[] newArray(int size) { 
     return new LocationPlus[size]; 
    } 
}; 

@Override 
public void writeToParcel(Parcel parcel, int flags) { 
    super.writeToParcel(parcel, flags); 
    parcel.writeInt(mBattery); 

} 

Answer 3

您好我已經做研究了很多關於這一點，但我找不到有用的東西。我嘗試下面的解決方案，它爲我工作。

假設你的超類只有名爲「mData」的int變量。

public class Location implements Parcelable { 
protected int mData; 

public int describeContents() { 
    return 0; 
} 

public void writeToParcel(Parcel out, int flags) { 
    out.writeInt(mData); 
} 

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

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

private Location(Parcel in) { 
    mData = in.readInt(); 
} 

}

然後，你的擴展類只有int變量命名爲 「mBattery」。

public class LocationPlus extends Location { 
protected int mBattery; 

public int describeContents() { 
    return 0; 
} 

public void writeToParcel(Parcel out, int flags) { 
    out.writeInt(mBattery); 
} 

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

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

private LocationPlus(Parcel in) { 
    mBattery = in.readInt(); 
} 

}

到目前爲止，LocationPlus工作正常。但是我們不設置超類的變量。首先，我使用super（..）方法在擴展類上設置了超類的變量。但它沒有奏效。

private LocationPlus(Parcel in) { 
    super(in); 
    mBattery = in.readInt(); 
} 

而不是上面的代碼，你應該明確地設置所有超類的變量。超級'變量應該受到保護。最終構造函數應該是這樣的：

private LocationPlus(Parcel in) { 
    mData = in.readIn(); 
    mBattery = in.readInt(); 
} 

和writeToParcel方法應該是這樣的：

public void writeToParcel(Parcel out, int flags) { 
    out.writeIn(mData); 
    out.writeInt(mBattery); 
} 

Answer 4

Parcelable的速度之王

根據google engineers，該代碼將運行明顯更快。其中一個原因是，我們正在明確序列化過程，而不是使用反射來推斷它。也有理由認爲代碼已經爲此目的進行了大量優化。

public abstract class BaseClass implements Parcelable { 

    public String FullName; 
    public boolean IsValidUser; 
    public String UserName; 


    public BaseClass() { 
    } 


    protected BaseClass(Parcel in) { 
     FullName = in.readString(); 
     IsValidUser = in.readByte() != 0; 
     UserName = in.readString(); 
    } 

    @Override 
    public void writeToParcel(Parcel dest, int flags) { 
     dest.writeString(FullName); 
     dest.writeByte((byte) (IsValidUser ? 1 : 0)); 
     dest.writeString(UserName); 
    } 
} 

兒童類會隨着名單使用添加到parcelable對象如下：

public class DerivedClass extends BaseClass { 

    public boolean IsSuccess; 
    public String Message; 
    public List<AnotherClass> AnotherClassObj; 


    public DerivedClass() { 
     super(); 
    } 

    protected DerivedClass(Parcel in) { 
     super(in); 
     AnotherClassObj = new ArrayList<AnotherClass>(); 
     IsSuccess = in.readByte() != 0; 
     Message = in.readString(); 
     AnotherClassObj = in.readArrayList(AnotherClass.class.getClassLoader()); 
    } 

    public static final Creator<DerivedClass> CREATOR = new Creator<DerivedClass>() { 
     @Override 
     public DerivedClass createFromParcel(Parcel in) { 
      return new DerivedClass(in); 
     } 

     @Override 
     public DerivedClass[] newArray(int size) { 
      return new DerivedClass[size]; 
     } 
    }; 

    @Override 
    public void writeToParcel(Parcel dest, int flags) { 
     super.writeToParcel(dest, flags); 
     dest.writeByte((byte) (IsSuccess ? 1 : 0)); 
     dest.writeString(Message); 
     dest.writeList(AnotherClassObj); 
    } 

    public int describeContents() { 
     return 0; 
    } 
} 

另一個孩子類：

public class AnotherClass extends BaseClass { 
    public AnotherClass() { 
     super(); 
    } 

    protected AnotherClass(Parcel in) { 
     super(in); 
    } 

    public int describeContents() { 
     return 0; 
    } 

    public static final Creator<AnotherClass> CREATOR = new Creator<AnotherClass>() { 
     @Override 
     public AnotherClass createFromParcel(Parcel in) { 
      return new AnotherClass(in); 
     } 

     @Override 
     public AnotherClass[] newArray(int size) { 
      return new AnotherClass[size]; 
     } 
    }; 

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

在活動：

Intent intent = new Intent(LoginActivity.this, MainActivity.class); 
intent.putExtra("UserObject", parcelableObject); 
startActivity(intent); 
finish(); 

在接受活動：

Bundle extras = getIntent().getExtras(); 
if (extras != null) { 
     userObject = extras.getParcelable("UserObject"); 
}