iOS 浅赋值、深复制、完全复制的知识点梳理验证(附加归档解档)

最新推荐文章于 2021-11-27 16:51:10 发布

转载最新推荐文章于 2021-11-27 16:51:10 发布 · 391 阅读

本文探讨了iOS开发中浅复制、深复制及完全复制的区别，通过代码验证了不同复制方式下多层对象的行为表现，并介绍了如何使用归档和解档实现完全复制。

转载请注明出处http://blog.youkuaiyun.com/zsk_zane

写于前：

在之前转载的一片文章中，文中对浅复制和深复制进行了详细的解读，同时还提到了深复制（one-level-deep copy）、完全复制（true copy）的概念，并指出iOS开发中的深复制是单层深赋值，本文将对这几个概念进行验证梳理。

（单层和完全概念区分：例如多层数组只实现一层内容拷贝，其他层为指针拷贝成为单层深复制；若多层内容都实现拷贝称为完全赋值）

程序中用到的几点概念补充

（1）

浅复制(shallow copy)：在浅复制操作时，对于被复制对象的每一层都是指针复制。
深复制(one-level-deep copy)：在深复制操作时，对于被复制对象，至少有一层是深复制。
完全复制(real-deep copy)：在完全复制操作时，对于被复制对象的每一层都是对象复制。

（2）

归档和解档的概念补充：
有时存在这样的需求，即将程序中使用的多个对象及其属性值，以及它们的相互关系保存到文件中，或者发送给另外的进程。为了实现此功能，foundation框架中，可以把相互关联的多个对象归档为二进制文件，而且还能将对象的关系从二进制文件中还原出来。

归档：将对象打包成二进制文件。NSKeyedArchiver：归档器
解档：归档的逆变换。NSKeyedUnarchiver：解档器
因此可以利用归档和解档来实现完全复制

代码验证

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//创建多层数组</span>
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSArray</span> *array = @[@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>];
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSArray</span> *oldArray = @[@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"xxxx"</span>,array];

    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//浅复制</span>
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSArray</span> *shallowArray = [oldArray copy];
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//深复制</span>
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSArray</span> *oneDeepLevelArray = [oldArray mutableCopy];
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//完全深复制，利用归档和解档的方式</span>
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSArray</span> *trueDeepCopyArray = [NSKeyedUnarchiver unarchiveObjectWithData:[NSKeyedArchiver archivedDataWithRootObject:oldArray]];</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

<code class="hljs mel has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    NSLog(<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@"</span><span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%p</span>,<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%p</span>,<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%p</span>,<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%p</span><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">",oldArray,shallowArray,oneDeepLevelArray,trueDeepCopyArray);</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

输出结果：

<code class="hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">0x7fc7e9c1c0d0,0x7fc7e9c1c0d0,0x7fc7e9c0c5c0,0x7fc7e9c22ef0</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

从上述打印地址可以看出：

浅复制只是简单的指针赋值，指向内存仍相同；
深复制，和完全深复制都实现了内容的复制，但是是否实现对被复制对象的每一层都复制，通过查看多层数组第二层元素的地址来验证：

<code class="hljs perl has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    NSLog(<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@"</span>shallow——<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%p</span>,<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%p</span><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">",oldArray[1][0],shallowArray[1][0]);
    NSLog(<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@"</span>oneDeep——<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%p</span>,<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%p</span>"</span>,oldArray[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>][<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>],oneDeepLevelArray[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>][<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>]);
    NSLog(<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@"</span>trueDeep——<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%p</span>,<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%p</span><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">",oldArray[1][0],trueDeepCopyArray[1][0]);
</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

输出结果：

<code class="hljs bash has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    shallow——<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>xb000000000000012,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>xb000000000000012
    oneDeep——<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>xb000000000000012,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>xb000000000000012
    <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">true</span>Deep——<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>xb000000000000012,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>xb000000000000013</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>