Parcelable 在何处/何时使用 describeContents()? [英] Parcelable where/when is describeContents() used?

问题描述

有谁知道Parcelable的这个方法在哪里/何时被调用?

Does anyone know where/when this method of a Parcelable is called?

@Override
public int describeContents() {
    return 0;
}

它必须被覆盖.但是我应该考虑用它做一些有用的事情吗?

It has to be overriden. But should I consider doing something useful with it?

推荐答案

Parcelable 中定义了一个名为 CONTENTS_FILE_DESCRIPTOR 的常量，用于describeContents() 创建位掩码返回值.

There is a constant defined in Parcelable called CONTENTS_FILE_DESCRIPTOR which is meant to be used in describeContents() to create bitmask return value.

API ref中对CONTENTS_FILE_DESCRIPTOR的描述是:

与 describeContents() 一起使用的位掩码:每个位代表一种在编组时被认为具有潜在特殊意义的对象.

Bit masks for use with describeContents(): each bit represents a kind of object considered to have potential special significance when marshalled.

这真正意味着:如果您需要将 FileDescriptor 对象放入 Parcelable，您应该/必须指定 CONTENTS_FILE_DESCRIPTOR 作为 describeContents() 的返回值，即通过特殊对象"(在 describeContents() 的描述中)它们的真正意思是:FileDescriptor.

Which really means: If you need to put FileDescriptor object into Parcelable you should/must specify CONTENTS_FILE_DESCRIPTOR as return value of describeContents(), i.e. by "special object" (in describeContents()'s description) they really mean: FileDescriptor.

整个Parcelable 功能看起来还没有完成(阅读:设计很糟糕).文档中还有一件奇怪的事情:

This whole Parcelable functionality looks unfinished (read: has bad design). There is one other strange thing in the docs:

实现 Parcelable 接口的类还必须有一个名为 CREATOR 的静态字段，它是一个实现 Parcelable.Creator 接口的对象

Classes implementing the Parcelable interface must also have a static field called CREATOR, which is an object implementing the Parcelable.Creator interface

通过以人类可读形式定义的规则实现多重继承?:-)

Implementing multiple inheritance by rules defined in human readable form? :-)

似乎 C++ 程序员设计了 Parceable 并且在某些时候他意识到:哦，该死，Java 中没有多重继承...... :-)

It seems like C++ programmer designed Parceable and at some point he realized: Oh, damn, there is no multiple inheritance in Java... :-)

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