【iOS】浅拷贝和深拷贝

浅拷贝和深拷贝

  • 浅拷贝即指针拷贝，可以认为是给一只狗加了一条绳子；深拷贝不但拷贝了对象的指针，还在系统中在分配了一块内存用来存放拷贝对象的内容，可以认为是产生了一条带绳子的新狗。即浅拷贝是两根绳子一条狗，深拷贝是两根绳子两条狗且每只狗对应各自的绳子。
  • 图示：
  • 深浅拷贝取决于拷贝后的对象是不是和被拷贝对象的地址相同，如果不同，则产生了新的对象，即为深拷贝。如果不同，则只是指针拷贝，相当于retain一次原对象，即为浅拷贝。

copy与mutableCopy

  • copy复制后的对象是不可变对象，mutableCopy复制后的对象是可变对象，与原始对象是否可变无关。

非集合类的copy与mutableCopy

  • 对不可变对象执行copy操作，是指针复制（浅拷贝），执行mutableCopy操作是内容复制（深拷贝）。
  • 对可变对象执行copy操作和mutableCopy操作都是内容复制（深拷贝）。
  • 代码表示如下：
[immutableObject copy];				// 浅复制
[immutableObject mutableCopy];  	// 深复制
[mutableObject copy];				// 深复制
[mutableObject mutableCopy]	;		// 深复制

容器类的浅复制和深复制

  • 容器对象和非容器对象类似，可变对象复制的都是一个新对象，不可变对象copy的是浅复制，mutableCopy是深复制
  • 对于容器而言，元素对象始终是指针复制。
  • 验证代码：
	NSMutableArray *array01 = [NSMutableArray arrayWithObjects:@"a",@"b",@"c", nil];
    NSArray *copyArray01 = [array01 copy];
    NSMutableArray *mutableCopyArray01 = [array01 mutableCopy];
    NSLog(@"array01 = %p,copyArray01 = %p",array01,copyArray01);
    NSLog(@"array01 = %p,mutableCopyArray01 = %p",array01,mutableCopyArray01);
    NSLog(@"==================================================================");
    [array01 addObject:@"d"];
    NSLog(@"array01 = %p,copyArray01 = %p",array01,copyArray01);
    NSLog(@"array01 = %p,mutableCopyArray01 = %p",array01,mutableCopyArray01);
    NSLog(@"array01 =%@\n copyArray01 =%@\n mutableCopyArray01 =%@",array01,copyArray01,mutableCopyArray01);
    NSLog(@"array01[0] = %p,array01[1] = %p,array01[2] = %p,array01[3] = %p",array01[0],array01[1],array01[2],array01[3]);
    NSLog(@"copyArray01[0] = %p,copyArray01[1] = %p,copyArray01[2] = %p",copyArray01[0],copyArray01[1],copyArray01[2]);
    NSLog(@"mutableCopyArray01[0] = %p,mutableCopyArray01[1] = %p,mutableCopyArray01[2] = %p",mutableCopyArray01[0],mutableCopyArray01[1],mutableCopyArray01[2]);
    NSLog(@"==================================================================");
    [mutableCopyArray01 addObject:@"e"];
    NSLog(@"array01 = %p,copyArray01 = %p",array01,copyArray01);
    NSLog(@"array01 = %p,mutableCopyArray01 = %p",array01,mutableCopyArray01);
    NSLog(@"array01 =%@\n copyArray01 =%@\n mutableCopyArray01 =%@",array01,copyArray01,mutableCopyArray01);
    NSLog(@"array01[0] = %p,array01[1] = %p,array01[2] = %p",array01[0],array01[1],array01[2]);
    NSLog(@"copyArray01[0] = %p,copyArray01[1] = %p,copyArray01[2] = %p",copyArray01[0],copyArray01[1],copyArray01[2]);
    NSLog(@"mutableCopyArray01[0] = %p,mutableCopyArray01[1] = %p,mutableCopyArray01[2] = %p,mutableCopyArray01[3] = %p",mutableCopyArray01[0],mutableCopyArray01[1],mutableCopyArray01[2],mutableCopyArray01[3]);
  • 打印结果：
2018-06-14 11:16:43.117758+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,copyArray01 = 0x604000443bd0
2018-06-14 11:16:43.117887+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,mutableCopyArray01 = 0x604000443a80
2018-06-14 11:16:43.118014+0800 copy_demo[1988:95724] ==================================================================
2018-06-14 11:16:43.118108+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,copyArray01 = 0x604000443bd0
2018-06-14 11:16:43.118323+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,mutableCopyArray01 = 0x604000443a80
2018-06-14 11:16:43.118485+0800 copy_demo[1988:95724] array01 =(
    a,
    b,
    c,
    d
)
 copyArray01 =(
    a,
    b,
    c
)
 mutableCopyArray01 =(
    a,
    b,
    c
)
2018-06-14 11:16:43.118559+0800 copy_demo[1988:95724] array01[0] = 0x10bf06128,array01[1] = 0x10bf06148,array01[2] = 0x10bf06168,array01[3] = 0x10bf061e8
2018-06-14 11:16:43.118661+0800 copy_demo[1988:95724] copyArray01[0] = 0x10bf06128,copyArray01[1] = 0x10bf06148,copyArray01[2] = 0x10bf06168
2018-06-14 11:16:43.118758+0800 copy_demo[1988:95724] mutableCopyArray01[0] = 0x10bf06128,mutableCopyArray01[1] = 0x10bf06148,mutableCopyArray01[2] = 0x10bf06168
2018-06-14 11:16:43.118891+0800 copy_demo[1988:95724] ==================================================================
2018-06-14 11:16:43.119034+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,copyArray01 = 0x604000443bd0
2018-06-14 11:16:43.119095+0800 copy_demo[1988:95724] array01 = 0x604000443cf0,mutableCopyArray01 = 0x604000443a80
2018-06-14 11:16:43.119185+0800 copy_demo[1988:95724] array01 =(
    a,
    b,
    c,
    d
)
 copyArray01 =(
    a,
    b,
    c
)
 mutableCopyArray01 =(
    a,
    b,
    c,
    e
)
2018-06-14 11:16:43.119346+0800 copy_demo[1988:95724] array01[0] = 0x10bf06128,array01[1] = 0x10bf06148,array01[2] = 0x10bf06168
2018-06-14 11:16:43.119527+0800 copy_demo[1988:95724] copyArray01[0] = 0x10bf06128,copyArray01[1] = 0x10bf06148,copyArray01[2] = 0x10bf06168
2018-06-14 11:16:43.119595+0800 copy_demo[1988:95724] mutableCopyArray01[0] = 0x10bf06128,mutableCopyArray01[1] = 0x10bf06148,mutableCopyArray01[2] = 0x10bf06168,mutableCopyArray01[3] = 0x10bf06288

深拷贝浅拷贝面试中也经常问到，这只是一个简单的理解和总结，除了这些，还有很多比较复杂的以及自定义对象的深复制和浅复制。
推荐一篇讲得比较详细和深刻的文章：https://github.com/pro648/tips/wiki/深复制、浅复制、copy、mutableCopy。我在整理这篇文章的时候也参考了这篇文章，感谢作者的分享。

posted @ 2018-06-14 11:27  colorful_flowers  阅读(158)  评论(0)  编辑  收藏  举报