当我尝试读取通过 Intent 传递的 Vector 时出现 NullPointerException

Question

我正在尝试使用 Parcelable classes 将 Stack 从 activity 提供给另一个。为此，我按以下方式定义了 MyStack 和 MyVector3。然后将其包含在模型 class.

中

型号class

public class Model implements Parcelable{
public List<MyStack> surfaces;
public Info info;

public Model (){}
public Model(List<MyStack> surf){
    surfaces = surf;
}

public void setInfo(Info i){
    info=i;
}

public Info getInfo(){
    return info;
}

public List<MyStack> getSurfaces(){
    return this.surfaces;
}

public int numSurfaces(){
    return surfaces.size();
}

public int describeContents() {
    return 0;
}

public void writeToParcel(Parcel out, int flags) {
    out.writeTypedList(surfaces);
    //Parcelable infoP = ((Parcelable) info);
    //out.writeParcelable(infoP, 0);
}

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

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

private Model(Parcel in) {
    surfaces = new ArrayList<MyStack>();
    in.readTypedList(surfaces, MyStack.CREATOR);
    //info = in.readParcelable(Info.class.getClassLoader());
}

public class Info{
    String title;
    String descr;

    public Info(String t, String d){
        title=t;
        descr=d;
    }

    public Info(String t){
        title=t;
    }

    public void setDescr(String d){
        descr=d;
    }
}

}

MyStack class

public class MyStack implements Parcelable {
public Stack<MyVector3> stack;

public MyStack(MyStack ms){
    this.stack=ms.stack;
}

public MyStack(Stack s){
    stack= s;
}

public Stack getStack(){
    return this.stack;
}

public int describeContents() {
    return 0;
}

public void writeToParcel(Parcel out, int flags) {
    out.writeTypedList(stack);
}

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

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

private MyStack(Parcel in) {
    stack= new Stack<MyVector3>();
    in.readTypedList(stack, MyVector3.CREATOR);
}

}

MyVector3 class

public class MyVector3 extends Vector3 implements Parcelable {
public Vector3 vector;

public MyVector3(Vector3 v){
    vector=v;
}

public MyVector3(double x, double y, double z){
    vector= new Vector3(x,y,z);
}

public Vector3 getVector(){
    return this.vector;
}

public int describeContents() {
    return 0;
}

public void writeToParcel(Parcel out, int flags) {
    out.writeDoubleArray(new double[]{
            this.x,
            this.y,
            this.z});
}

public static final Parcelable.Creator<MyVector3> CREATOR
        = new Parcelable.Creator<MyVector3>() {
    public MyVector3 createFromParcel(Parcel in) {
        return new MyVector3(in);
    }

    public MyVector3[] newArray(int size) {
        return new MyVector3[size];
    }
};

private MyVector3(Parcel in) {
    double[] data = new double[3];
    in.readDoubleArray(data);

    this.x= data[0];
    this.y= data[1];
    this.z= data[2];
}

}

这是意图创建，其中模型填充良好，我从日志中正确获取所有值

Model model= new Model(surfaces);

    Intent intent = new Intent(this, EditorPresenter.class);
    intent.putExtra("model", model);
    startActivity(intent);

以及我在哪里使用它

 Intent intent = getIntent();
    model= intent.getParcelableExtra("model");
    MyStack[] sf = model.surfaces.toArray(new MyStack[model.numSurfaces()]);
    //surf = new Stack();
    surf = new Stack[model.numSurfaces()];
    Log.i(TAG, "ss="+Integer.toString(sf.length));  //expected value
    for(int s=0; s<sf.length; s++) {
        Log.i(TAG, "s="+Integer.toString(s));     //expected value
        Stack st= new Stack();
        Log.i(TAG, "vv="+Integer.toString(sf[s].getStack().size()));     //expected value
        for(int v=0; v<sf[s].getStack().size(); v++) {
            Log.i(TAG, "v="+Integer.toString(v) +sf[s].stack.elementAt(v).getVector().toString());  //NullPointerException
            MyVector3 mv = (MyVector3) sf[s].stack.elementAt(v);
            if(mv!=null) st.add(mv.getVector());
        }
        surf[s]=st;
    }

但每当我尝试 read/write Vector3 值时，我都会收到 NullPointerException。

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String org.rajawali3d.math.vector.Vector3.toString()' on a null object reference

问题可能出在 Parcelable classes 中，直到我从意图中得到错误的模型（预期的面数和顶点数是正确的，矢量值可能为空）。非常感谢任何帮助。

Answer 1

从 parcelable 读取后，您没有实例化 Vector 对象。变化

private MyVector3(Parcel in) {
  double[] data = new double[3];
  in.readDoubleArray(data);

  this.x= data[0];
  this.y= data[1];
  this.z= data[2];
}

和

private MyVector3(Parcel in) {
    double[] data = new double[3];
    in.readDoubleArray(data);

    this.x= data[0];
    this.y= data[1];
    this.z= data[2];
    vector = new Vector3(x,y,z);
}

Answer 2

您可以使用此工具从您的代码生成 Parcelable 类 http://www.parcelabler.com/，然后使用新生成的类.

再试一次

当我尝试读取通过 Intent 传递的 Vector 时出现 NullPointerException

NullPointerException when I try to read a Vector passed through Intent

java

android

nullpointerexception

parcelable

android-intent