读取和放大器; Parcelable对象的写作阵列 [英] Read & writing arrays of Parcelable objects

问题描述

我有下面的类读取和写入对象的数组从/到一个包裹：

I have following class which reads and writes an array of objects from/to a parcel:

class ClassABC extends Parcelable {
    MyClass[] mObjList;

    private void readFromParcel(Parcel in) {
        mObjList = (MyClass[]) in.readParcelableArray(
                com.myApp.MyClass.class.getClassLoader()));
    }

    public void writeToParcel(Parcel out, int arg1) {
        out.writeParcelableArray(mObjList, 0);
    }

    private ClassABC(Parcel in) {
        readFromParcel(in);
    }

    public int describeContents() {
        return 0;
    }

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

        public ClassABC createFromParcel(Parcel in) {
            return new ClassABC(in);
        }

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

在上面的code，我收到了 ClassCastException异常阅读时 readParcelableArray ：

In above code I get a ClassCastException when reading readParcelableArray:

ERROR / AndroidRuntime（5880）：java.lang.ClassCastException：产生的原因[Landroid.os.Parcelable;

ERROR/AndroidRuntime(5880): Caused by: java.lang.ClassCastException: [Landroid.os.Parcelable;

什么是错在上述code？在写对象的数组，我应该首先将阵列的的ArrayList ？

What is wrong in above code? While writing the object array, should I first convert the array to an ArrayList?

更新：

是否确定对象数组转换为的ArrayList ，并将其添加到包裹？例如，书写时：

Is it OK to convert an Object array to an ArrayList and add it to parcel? For instance, when writing:

    ArrayList<MyClass> tmpArrya = new ArrayList<MyClass>(mObjList.length);
    for (int loopIndex=0;loopIndex != mObjList.length;loopIndex++) {
        tmpArrya.add(mObjList[loopIndex]);
    }
    out.writeArray(tmpArrya.toArray());

当阅读：

    final ArrayList<MyClass> tmpList = 
            in.readArrayList(com.myApp.MyClass.class.getClassLoader());
    mObjList= new MyClass[tmpList.size()];
    for (int loopIndex=0;loopIndex != tmpList.size();loopIndex++) {
        mObjList[loopIndex] = tmpList.get(loopIndex);
    }

但现在我得到一个 NullPointerException异常。是上面的做法是正确的？为什么它是抛出一个NPE？

But now I get a NullPointerException. Is above approach is correct? Why it is throwing an NPE?

推荐答案

您需要使用 Parcel.writeTypedArray（）方法写入阵列，并与读回 Parcel.createTypedArray（）的方法，像这样：

You need to write the array using the Parcel.writeTypedArray() method and read it back with the Parcel.createTypedArray() method, like so:

MyClass[] mObjList;

public void writeToParcel(Parcel out) {
    out.writeTypedArray(mObjList, 0);
}

private void readFromParcel(Parcel in) {
    mObjList = in.createTypedArray(MyClass.CREATOR);
}

为什么你不应该使用 readParcelableArray（） / writeParcelableArray（）方法的原因是， readParcelableArray（）真正创建一个 Parcelable [] 结果。这意味着你可以不投的方法的结果为 MyClass的[] 。相反，你必须创建相同的长度作为结果的 MyClass的数组和复制的每个元素从结果数组的 MyClass的阵列。

The reason why you shouldn't use the readParcelableArray()/writeParcelableArray() methods is that readParcelableArray() really creates a Parcelable[] as a result. This means you cannot cast the result of the method to MyClass[]. Instead you have to create a MyClass array of the same length as the result and copy every element from the result array to the MyClass array.

Parcelable[] parcelableArray =
        parcel.readParcelableArray(MyClass.class.getClassLoader());
MyClass[] resultArray = null;
if (parcelableArray != null) {
    resultArray = Arrays.copyOf(parcelableArray, parcelableArray.length, MyClass[].class);
}

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