爲自定義2D陣列實現Parcelable

Question

爲了在新活動中傳遞我的2D陣列，我提出了包裝它並實現接口的方法。不幸的是，當我使用Intent.getParcelableExtra時，我得到了java.lang.NullPointerException，這意味着我當然不會實現接口權限。下面是我更新代碼

public class MazeMapParcelable implements Parcelable 
{ 
private Cell[][] mazeMap; 

public MazeMapParcelable(Cell[][] mazeMap) 
{ 
    this.mazeMap = mazeMap; 
} 

public Cell[][] getMazeMap() 
{ 
    return this.mazeMap; 
} 


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

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

public void writeToParcel(Parcel dest, int flags) 
{ 
    int width = mazeMap.length; 
    dest.writeInt(width); 
    int height = mazeMap[1].length; 
    dest.writeInt(height); 

    for(int i=0;i<width;i++) 
    { 
     for(int j=0;j<height;j++) 
     { 
      dest.writeInt(mazeMap[i][j].getCordX()); 
      dest.writeInt(mazeMap[i][j].getCordY()); 
      dest.writeByte((byte) (mazeMap[i][j].getNorthWall() ? 1 : 0)); 
      dest.writeByte((byte) (mazeMap[i][j].getSouthWall() ? 1 : 0)); 
      dest.writeByte((byte) (mazeMap[i][j].getEastWall() ? 1 : 0)); 
      dest.writeByte((byte) (mazeMap[i][j].getWestWall() ? 1 : 0)); 
     } 
    } 
} 

public int describeContents() 
{ 
    return 0; 
} 

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

private MazeMapParcelable(Parcel in) 
{ 
    int width = in.readInt(); 
    int height = in.readInt(); 
    Cell[][] recreatedMazeMap = new Cell[width][height]; 

    for(int i=0;i<width;i++) 
    { 
     for(int j=0;j<height;j++) 
     { 
      int cordX = in.readInt(); 
      int cordY = in.readInt(); 
      boolean northWall = in.readByte() != 0; 
      boolean southWall = in.readByte() != 0; 
      boolean westWall = in.readByte() != 0; 
      boolean eastWall = in.readByte() != 0; 
      Cell currCell = new Cell(cordX,cordY,northWall,southWall,westWall,eastWall); 
      recreatedMazeMap[i][j] = currCell; 
     } 
    } 
    mazeMap = recreatedMazeMap; 
} 

請注意，我的手機類成員分別是：

protected int x; 
protected int y; 

private boolean northWall; 
private boolean southWall; 
private boolean westWall; 
private boolean eastWall; 
private boolean bomb; 
private boolean deadEnd; 

更新我不再獲得空指針異常，但我的數據不正確寫入，因爲他們應該。 （parceableMazeMap[0][0] != originalMazeMap[0][0]）

Answer 1

也許你想看看使用writeTypedArray()。如果在Cell對象中實現Parcelable，則可以使用writeTypedArray（）將它們保存到Parcel。

---

當parcelable試圖重新創建實例，調用此構造函數：

private MazeMapParcelable(Parcel in){ 
    ... 
} 

但你從來沒有真正在這一點上初始化您的數組。所以它仍然是在這種狀態下（這是空）：

private Cell[][] mazeMap; 

由於mazeMap在這種狀態下沒有初始化，它不會有任何長度。所以這段代碼不會給你你所期望的值：

int width = this.mazeMap.length; 
int height = this.mazeMap[1].length; 

試着寫寬度&高度值作爲parcelable第一項，然後閱讀它們，當你重新創建parcelable。