如何使用嵌套对象创建一个类Parcelable

Question

我想让A级Parcelable.

public class A {
    public String str;
    public ArrayList<B> list;
}

这是我到目前为止所提出的.但是它崩溃了NullPointerException.问题是这两个陈述:dest.writeList(list);&in.readList(list, this.getClass().getClassLoader());.我无法弄清楚从这里做什么:(

A级

public class A implements Parcelable {
    public String str;
    public ArrayList<B> list;

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

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(str);
        dest.writeList(list);
    }

    private A(Parcel in) {
        str = in.readString();
        in.readList(list, this.getClass().getClassLoader());
    }

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

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

B级

public class B implements Parcelable {
    public String str;

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

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

    private B(Parcel in) {
        str = in.readString();
    }

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

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

感谢您的时间.

Answer 1

我终于找到了输入Google的内容:),并发现了这个Android,如何在Parcelable类中正确使用readTypedList方法？

解决方案是使用read-/writeTypedList.我还初始化arraylist以避免任何进一步的NullPointerException.

A级

public class A implements Parcelable {
    public String str;
    public ArrayList<B> list = new ArrayList<B>();

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

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(str);
        dest.writeTypedList(list);
    }

    private A(Parcel in) {
        str = in.readString();
        in.readTypedList(list, B.CREATOR);
    }

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

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

B级

public class B implements Parcelable {
    public String str;

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

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

    private B(Parcel in) {
        str = in.readString();
    }

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

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

Answer 2

如果主对象中只有一个Parcelable对象Parcelable,则不会像接受的答案一样列出.然后它将如下所示:

A级

public class A implements Parcelable {
    public String str;
    public B objectB;

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

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        //The parcelable object has to be the first one
        dest.writeParcelable(objectB, flags);
        dest.writeString(str);
    }

    private A(Parcel in) {
        this.objectB = in.readParcelable(B.class.getClassLoader());
        str = in.readString();
    }

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

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

B级

public class B implements Parcelable {
    public String str;

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

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

    private B(Parcel in) {
        str = in.readString();
    }

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

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

重要提示: 请注意您编写和阅读Parcelable对象的顺序很重要.查看此答案以获取更多详细信息