私有成员属性

ObjC的私有成员属性

iOS的ObjC的私有属性，指的是：

• 大括号{}内部的
  • 属性名往往是以下划线开头的
• 且外部没有对应的同名的@property的属性

举例

AAURLSession

@interface AAURLSession : NSObject <NSURLSessionDataDelegate, NSURLSessionDelegate, NSURLSessionTaskDelegate>
{
...
    NSObject<OS_dispatch_queue> *_sessionQueue;
...
}

WAPreparedRegistrationURL

WhatsApp/headers/WhatsApp_v23.20.79_headers_WhatsApp/WAPreparedRegistrationURL.h

#import <objc/NSObject.h>

@class NSArray, NSString, NSURL;

@interface WAPreparedRegistrationURL : NSObject
{
    NSString *_baseURLString;
    NSArray *_params;
    NSURL *_proxyURL;
}

- (void).cxx_destruct;
- (id)urlWithTokenArray:(id)arg1;
- (id)urlWithRegistrationToken:(id)arg1 backupToken:(id)arg2;
- (id)initWithBaseURLString:(id)arg1 params:(id)arg2 encryptWithProxyURL:(id)arg3;

@end

-》

• 类WAPreparedRegistrationURL的私有属性
  • _baseURLString
  • _params
  • _proxyURL

访问私有成员属性的方式

下面以WAPreparedRegistrationURL为例，来介绍有多种方式可以查看私有成员属性值：

Xcode调试时，有对应的类的实例：

(lldb) po 0x0000000282170b80
<WAPreparedRegistrationURL: 0x282170b80>

想要查看：

• 类的WAPreparedRegistrationURL的私有属性=成员=变量的值
  • _baseURLString

具体方式：

valueForKey

• 语法：po [objcObj valueForKey: @"_xxx"]

  • 属性名不带下划线也可以：po [objcObj valueForKey: @"xxx"]

• 举例

(lldb) po [0x282170b80 valueForKey: @"_baseURLString"]
https://v.whatsapp.net/v2/exist

(lldb) po [0x282170b80 valueForKey: @"baseURLString"]
https://v.whatsapp.net/v2/exist

指针

• 语法

  po ((ClassName*)instanceAddress)->privatePropertyName
  

• 举例

  (lldb) po ((WAPreparedRegistrationURL*)0x282170b80)->_baseURLString
  https://v.whatsapp.net/v2/exist
  

偏移量+内存值 == 自己计算指针和内存中的值

(lldb) p/x 0x282170b80 + 0x08
(long) $18 = 0x0000000282170b88
(lldb) x/2gx 0x0000000282170b88
0x282170b88: 0x00000002833bbf80 0x000000028680ed90
(lldb) po 0x00000002833bbf80
https://v.whatsapp.net/v2/exist

其中：

• 0x282170b80 + 0x08 == ((*WAPreparedRegistrationURL)0x282170b80)->_baseURLString
• 而内存地址是：0x00000002833bbf80
  • 其中保存的内容，就是：NSString*类型的URL值了

常见错误

• 用点.去访问：不带下划线，是无法访问的

(lldb) po ((WAPreparedRegistrationURL*)0x282170b80).baseURLString
error: expression failed to parse:
error: <user expression 23>:1:43: property 'baseURLString' not found on object of type 'WAPreparedRegistrationURL *'
((WAPreparedRegistrationURL*)0x282170b80).baseURLString
                                          ^

• 用点.去访问：带下划线，虽然也可以打印出值的
  • 但其实语法是错误的，但会自动会告诉你正确的语法：用指针->访问

(lldb) po ((WAPreparedRegistrationURL*)0x282170b80)._baseURLString
https://v.whatsapp.net/v2/exist

  Fix-it applied, fixed expression was: 
    ((WAPreparedRegistrationURL*)0x282170b80)->_baseURLString

• po无法，以ObjC的语法，去直接查看属性名（不论是带下划线还是不带下划线）-》 都会报错

(lldb) po [0x282170b80 baseURLString]
error: Execution was interrupted, reason: Attempted to dereference an invalid ObjC Object or send it an unrecognized selector.
The process has been returned to the state before expression evaluation.

(lldb) po [0x282170b80 _baseURLString]
error: Execution was interrupted, reason: Attempted to dereference an invalid ObjC Object or send it an unrecognized selector.
The process has been returned to the state before expression evaluation.

• 用指针访问时，不带下划线的话，会报报语法错误：找不到属性名=成员名=member

(lldb) po ((WAPreparedRegistrationURL*)0x282170b80)->baseURLString
error: expression failed to parse:
error: <user expression 17>:1:44: 'WAPreparedRegistrationURL' does not have a member named 'baseURLString'
((WAPreparedRegistrationURL*)0x282170b80)->baseURLString
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  ^

即可。