获取更多信息p po

• p & po
  po广泛用于OC和Swift的调试中用于输出变量、对象的值、地址或者description信息。

po -- Evaluate an expression on the current thread. Displays any
returned value with formatting controlled by the type's author.

在MasterViewController.swift中添加断点并重写description方法

  override var description: String {
    return "Yay! debugging " + super.description
  }
//  override var debugDescription: String {
//    return "debugDescription: " + super.debugDescription
//  }

MasterViewController

(lldb) po self
// 相当于调用了 description方法
Yay! debugging <Signals.MasterViewController: 0x7feae9e13140>

如果打开上文中debugDescription的注释这po self调的是debugDescription。
可以看出po在默认情况下是调用实例对象的description方法的，在重写了debugDescription的时候才调用debugDescription。通过image lookup命令可以查看哪些模块是重写的debugDescription的

(lldb)  image lookup -rn '\ debugDescription\]'

24 matches found in /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/Library/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/Foundation.framework/Foundation:
        Address: Foundation[0x0000000000007130] (Foundation.__TEXT.__text + 23312)
        Summary: Foundation`-[NSAffineTransform debugDescription]        Address: Foundation[0x000000000000b57e] (Foundation.__TEXT.__text + 40798)
        Summary: Foundation`-[NSArray(NSArray) debugDescription]        Address: Foundation[0x0000000000010861] (Foundation.__TEXT.__text + 62017)
        Summary: Foundation`+[NSBundle debugDescription]        Address: Foundation[0x00000000000202cd] (Foundation.__TEXT.__text + 126125)
...

(lldb) po self.view!.layer.description
"<CALayer: 0x6000005af740>"

(lldb) po self.view!.layer
<CALayer:0x6000005af740; position = CGPoint (187.5 333.5); bounds = CGRect (0 0; 375 667); delegate = <UITableView: 0x7f8165060600; frame = (0 0; 375 667); clipsToBounds = YES; autoresize = W+H; gestureRecognizers = <NSArray: 0x600000bb9d70>; layer = <CALayer: 0x6000005af740>; 
contentOffset: {0, 0}; contentSize: {0, 0}; adjustedContentInset: {0, 0, 0, 0}>; sublayers = (<CALayer: 0x6000005a9980>, <CALayer: 0x6000005afc00>); masksToBounds = YES; allowsGroupOpacity = YES; backgroundColor = <CGColor 0x6000021e0c60> 
[<CGColorSpace 0x6000021eb180> (kCGColorSpaceICCBased; kCGColorSpaceModelRGB; sRGB IEC61966-2.1; extended range)] ( 0.980392 0.980392 0.980392 1 ); _uikit_viewPointer = <UITableView: 0x7f8165060600; frame = (0 0; 375 667); clipsToBounds = YES; 
autoresize = W+H; gestureRecognizers = <NSArray: 0x600000bb9d70>; layer = <CALayer: 0x6000005af740>; contentOffset: {0, 0}; contentSize: {0, 0}; adjustedContentInset: {0, 0, 0, 0}>>

可以看出在不同的类中用po 或者直接调用description输出的信息是不一样的。

p -- Evaluate an expression on the current thread. Displays any
returned value with LLDB's default formatting.

在同样的断点出 p self

(lldb) p self
(Signals.MasterViewController) $R16 = 0x00007f8164d14f00 {
  UIKit.UITableViewController = {
    baseUIViewController@0 = <extracting data from value failed>
    _tableViewStyle = 0
    _keyboardSupport = nil
    _staticDataSource = nil
    _filteredDataSource = 0x0000600000bbc330
    _filteredDataType = 0
  }
  detailViewController = nil
}

在Swfit项目中采用OC语法会报错，可以通过expression 命令告诉lldb采用OC的语法

(lldb)expression -l objc -O -- [UIApplication sharedApplication]