【Harmony OS】【JAVA UI】鸿蒙系统中怎么使用Parcel进行存储数据或数据传递

 Parcel简介

在IPC过程中，发送方可以使用Parcel提供的写方法，将待发送的数据以特定格式写入Parcel对象。接收方可以使用Parcel提供的读取方法从Parcel对象中读取特定格式的数据。

Parcel实例的默认容量为200KB。如果您想要更多或更少，请使用setCapacity(int)更改它。

注意：只有以下数据类型的数据才能写入或从包裹中读取： byte, byteArray, short, shortArray, int, intArray, long, longArray, float, floatArray, double, doubleArray, boolean, booleanArray, char, charArray, String, StringArray、 PlainBooleanArray, Serializable, Sequenceable, 和 SequenceableArray。

方法介绍

2.1 addAppClassLoader(ClassLoader newClassLoader)public void addAppClassLoader（ClassLoader newClassLoader）添加第三方ClassLoader用于实例初始化。如果您需要封装或取消封装自定义序列化数据，请添加您自己的ClassLoader。

2.2 writeSequenceablepublic final void writeSequenceable(Sequenceable val)将可序列化对象写入Parcel实例。其余的方法参考文档Parcel资料

封装Sequenceable实体类我们参考Sequenceable资料

动手实践

今天将一个Sequenceable的集合存到Parcel然后读取出来
4.1 新建两个类 A类用户存放具体属性，B类用于存放A的实体类集合
A类代码如下

 public static class A implements Sequenceable {
   private int a;
 
private int b;
 
private int c;
 
public A() {
    this(0, 0, 0);
}
 
public A(int a, int b, int c) {
    this.a = a;
    this.b = b;
    this.c = c;
}
 
@Override
public boolean hasFileDescriptor() {
    return false;
}
 
@Override
public boolean marshalling(Parcel out) {
    out.writeInt(a);
    out.writeInt(b);
    out.writeInt(c);
    return true;
}
 
@Override
public boolean unmarshalling(Parcel in) {
    a = in.readInt();
    b = in.readInt();
    c = in.readInt();
    return true;
}
 
public static final Sequenceable.Producer PRODUCER = new Sequenceable.Producer() {
    public A createFromParcel(Parcel in) {
        A instance = new A();
        instance.unmarshalling(in);
        return instance;
    }
};
 
@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    A a1 = (A) o;
    return a == a1.a &&
            b == a1.b &&
            c == a1.c;
}
 
@Override
public int hashCode() {
    return Objects.hash(a, b, c);
}
 
@Override
public String toString() {
    return "A{" +
            "a=" + a +
            ", b=" + b +
            ", c=" + c +
            '}';
}

    public static class B implements Sequenceable {
    private List list;
         private B() {
    }
 
    private B(List list) {
        this.list = list;
    }
 
    @Override
    public boolean hasFileDescriptor() {
        return false;
    }
 
    @Override
    public boolean marshalling(Parcel out) {
        out.writeSequenceableList(list);
        return true;
    }
 
    @Override
    public boolean unmarshalling(Parcel in) {
        in.addAppClassLoader(getClass().getClassLoader());
        list = in.readSequenceableList(A.class);
        return true;
    }
 
    public static final Sequenceable.Producer PRODUCER = new Sequenceable.Producer() {
        public B createFromParcel(Parcel in) {
            B instance = new B();
            instance.unmarshalling(in);
            return instance;
        }
    };
 
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        B b = (B) o;
        return Objects.equals(list, b.list);
    }
 
    @Override
    public int hashCode() {
        return Objects.hash(list);
    }
}

<DirectionalLayout
    xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:height="match_parent"
    ohos:width="match_parent"
    ohos:orientation="vertical">
 
    <Text
        ohos:id="$+id:bt1"
        ohos:height="100vp"
        ohos:background_element="#Ed6262"
        ohos:width="match_parent"
        ohos:text_alignment="center"
        ohos:text_size="30fp"
        ohos:text_color="#ffffff"
        ohos:text="存储数据"/>
    <Text
        ohos:top_margin="10vp"
        ohos:id="$+id:Result"
        ohos:height="100vp"
        ohos:multiple_lines="true"
        ohos:width="match_parent"
        ohos:text_alignment="center|left"
        ohos:text_size="20fp"
        ohos:text_color="#ed6262"
        />
DirectionalLayout>

 findComponentById(ResourceTable.Id_bt1).setClickedListener(new Component.ClickedListener() {
            @Override
            public void onClick(Component component) {
                List list = new ArrayList<>();
                A a = new A(1, 2, 3);
                A a2 = new A(2, 2, 3);
                A a3 = new A(3, 2, 3);
                list.add(a);
                list.add(a2);
                list.add(a3);
                B b = new B(list);
                Parcel parcel = Parcel.create();
                parcel.writeSequenceable(b);
                B b1 = new B();
                parcel.readSequenceable(b1);
                StringBuilder stringBuilder=new StringBuilder();
                if (b1.list.size() > 0) {
                    for (int i = 0; i < b1.list.size(); i++) {
                        stringBuilder.append(" b1.list====>" + b1.list.get(i).toString());
                        stringBuilder.append("\n");
                    }
                }
                mResult.setText(stringBuilder.toString());
            }
        });