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所以我一直在看 StackOverFlow，似乎找不到完全解决我问题的话题。许多人在尝试使用自定义 Parcelable 时遇到空指针异常问题。我已经看到通过将静态添加到 parcelable 类中的 CREATOR 等简单的解决方案解决了问题。但是，我没有找到任何可以帮助我的事业或对我的处境有所启发的东西。

从名为 MyPointsList 的自定义类访问坐标的 ArrayList 时，出现空指针异常。在通过 MyPointsList 之前，我可以访问 MyPointsList 中的 ArrayList。检索实例后，我快速检查以确保实例不为空，它不是，然后继续访问我得到空指针异常的 ArrayList。

为什么我在访问 MyPointsList 中的 ArrayList 时在接收类中收到空指针异常？

以下是以下类的代码：

MyPoint.java

public class MyPoint implements Parcelable {
    private int x;
    private int y;

    public MyPoint(){
        this.x = 0;
        this.y = 0;
    }

    public MyPoint(Parcel in){
        this.x = 0;
        this.y = 0;
        readFromParcel(in);
    }

    public void setPoint(int px, int py){
        this.x = px;
        this.y = py;
    }

    public int getX(){return this.x;}

    public int getY(){return this.y;}

    public static final Parcelable.Creator <MyPoint> CREATOR = new Parcelable.Creator <MyPoint> (){
        public MyPoint createFromParcel(Parcel source) {
            // TODO Auto-generated method stub
            return new MyPoint(source);
        }

        public MyPoint[] newArray(int size) {
            // TODO Auto-generated method stub
            return new MyPoint[size];
        }       
    };

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

    public void writeToParcel(Parcel dest, int flags) {
        dest.writeInt(x);
        dest.writeInt(y);

    }

public void readFromParcel(Parcel in){
        int count = in.dataAvail();
        for(int i = 0; i < count; i++){
            x = in.readInt();
            i++;
            y = in.readInt();
        }
    }
}

MyPointsList.java

public class MyPointsList implements Parcelable {

    private ArrayList<MyPoint> arrList = new ArrayList<MyPoint>();
    private int myInt = 0;
    private String myString = null;

    public String getString(){return myString;}

    public void setString(String str){this.myString = str;}

    public MyPoint getMyPoint(int index){return this.arrList.get(index);}

    public ArrayList<MyPoint> getArrayList(){return arrList;}

    public void setArrayList(ArrayList<MyPoint> arr){this.arrList = arr;}

    public int getMyInt(){return myInt;}

    public void setMyInt(int newInt){this.myInt = newInt;}

    MyPointsList(){this.arrList = new ArrayList<MyPoint>();}

    public MyPointsList(Parcel in){
        myInt = in.readInt();
        myString = in.readString();
        arrList = new ArrayList<MyPoint>();
        in.readTypedList(arrList, MyPoint.CREATOR);
    }

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

    public void writeToParcel(Parcel out, int flags) {
        // TODO Auto-generated method stub
        out.writeInt(myInt);
        out.writeString(myString);
        out.writeTypedList(arrList);
    }

    public static final Parcelable.Creator<MyPointsList> CREATOR = new Parcelable.Creator<MyPointsList>(){

        public MyPointsList createFromParcel(Parcel source) {
            // TODO Auto-generated method stub
            return new MyPointsList(source);
        }

        public MyPointsList[] newArray(int size) {
            // TODO Auto-generated method stub
            return new MyPointsList[size];
        }   
    };
}

打包段：points 是 MyPoints 的 ArrayList

public void onClick(View v){
    MyPointsList object = new MyPointsList();
        object.setMyInt(100);
        object.setArrayList(points);
        Log.d("DEBUG", object.getMyPoint(5).getX() + " " + object.getMyPoint(5).getY() + " ");
        Intent goBack = new Intent(SignHereActivity.this, Menu.class);
        goBack.putExtra("parcel" , object);             
        SignHereActivity.this.startActivity(goBack);
    }
});

检索段

public void getIntentData(){
    Intent i = this.getIntent();
    if(i.hasExtra("parcel")){
        Bundle b = getIntent().getExtras();
        object = b.getParcelable("parcel");
        Log.d("Debug", object.getArrayList().get(5).getX() + " " + object.getArrayList().get(5).getY());
    }
}

如前所述，我一直在浏览我能找到的与我的问题相关的任何信息。我非常感谢任何输入和响应。对于我的代码中任何烦人的语法或令人困惑的部分，我深表歉意。作为一个整体，我对 java 和 Android 还是很陌生。

谢谢！

4

1 回答 1

0

我觉得自己像个傻瓜，但是如果其他人偶然发现了这一点，这就是解决方案。

从 MyPoint 中删除：

public void readFromParcel(Parcel in){
    int count = in.dataAvail();
    for(int i = 0; i < count; i++){
        x = in.readInt();
        i++;
        y = in.readInt();
    }
}

插入到 MyPoint：

public void readFromParcel(Parcel in){
    x = in.readInt();
    y = in.readInt();
}

就是这样。

于 2013-01-07T17:37:36.303 回答