README.md
1 Protocol Buffers - Google's data interchange format 2 =================================================== 3 4 [](https://travis-ci.org/google/protobuf) 5 6 Copyright 2008 Google Inc. 7 8 This directory contains the Objective C Protocol Buffers runtime library. 9 10 Requirements 11 ------------ 12 13 The Objective C implementation requires: 14 15 - Objective C 2.0 Runtime (32bit & 64bit iOS, 64bit OS X). 16 - Xcode 7.0 (or later). 17 - The library code does *not* use ARC (for performance reasons), but it all can 18 be called from ARC code. 19 20 Installation 21 ------------ 22 23 The full distribution pulled from github includes the sources for both the 24 compiler (protoc) and the runtime (this directory). To build the compiler 25 and run the runtime tests, you can use: 26 27 $ objectivec/DevTools/full_mac_build.sh 28 29 This will generate the `src/protoc` binary. 30 31 Building 32 -------- 33 34 There are two ways to include the Runtime sources in your project: 35 36 Add `objectivec/\*.h` & `objectivec/GPBProtocolBuffers.m` to your project. 37 38 *or* 39 40 Add `objectivec/\*.h` & `objectivec/\*.m` except for 41 `objectivec/GPBProtocolBuffers.m` to your project. 42 43 44 If the target is using ARC, remember to turn off ARC (`-fno-objc-arc`) for the 45 `.m` files. 46 47 The files generated by `protoc` for the `*.proto` files (`\*.pbobjc.h' and 48 `\*.pbobjc.m`) are then also added to the target. 49 50 Usage 51 ----- 52 53 The objects generated for messages should work like any other Objective C 54 object. They are mutable objects, but if you don't change them, they are safe 55 to share between threads (similar to passing an NSMutableDictionary between 56 threads/queues; as long as no one mutates it, things are fine). 57 58 There are a few behaviors worth calling out: 59 60 A property that is type NSString\* will never return nil. If the value is 61 unset, it will return an empty string (@""). This is inpart to align things 62 with the Protocol Buffers spec which says the default for strings is an empty 63 string, but also so you can always safely pass them to isEqual:/compare:, etc. 64 and have deterministic results. 65 66 A property that is type NSData\* also won't return nil, it will return an empty 67 data ([NSData data]). The reasoning is the same as for NSString not returning 68 nil. 69 70 A property that is another GPBMessage class also will not return nil. If the 71 field wasn't already set, you will get a instance of the correct class. This 72 instance will be a temporary instance unless you mutate it, at which point it 73 will be attached to its parent object. We call this pattern *autocreators*. 74 Similar to NSString and NSData properties it makes things a little safer when 75 using them with isEqual:/etc.; but more importantly, this allows you to write 76 code that uses Objective C's property dot notation to walk into nested objects 77 and access and/or assign things without having to check that they are not nil 78 and create them each step along the way. You can write this: 79 80 ``` 81 - (void)updateRecord:(MyMessage *)msg { 82 ... 83 // Note: You don't have to check subMessage and otherMessage for nil and 84 // alloc/init/assign them back along the way. 85 msg.subMessage.otherMessage.lastName = @"Smith"; 86 ... 87 } 88 ``` 89 90 If you want to check if a GPBMessage property is present, there is always as 91 `has\[NAME\]` property to go with the main property to check if it is set. 92 93 A property that is of an Array or Dictionary type also provides *autocreator* 94 behavior and will never return nil. This provides all the same benefits you 95 see for the message properties. Again, you can write: 96 97 ``` 98 - (void)updateRecord:(MyMessage *)msg { 99 ... 100 // Note: Just like above, you don't have to check subMessage and otherMessage 101 // for nil and alloc/init/assign them back along the way. You also don't have 102 // to create the siblingsArray, you can safely just append to it. 103 [msg.subMessage.otherMessage.siblingsArray addObject:@"Pat"]; 104 ... 105 } 106 ``` 107 108 If you are inspecting a message you got from some other place (server, disk, 109 etc), you may want to check if the Array or Dictionary has entries without 110 causing it to be created for you. For this, there is always a `\[NAME\]_Count` 111 property also provided that can return zero or the real count, but won't trigger 112 the creation. 113 114 For primitive type fields (ints, floats, bools, enum) in messages defined in a 115 `.proto` file that use *proto2* syntax there are conceptual differences between 116 having an *explicit* and *default* value. You can always get the value of the 117 property. In the case that it hasn't been set you will get the default. In 118 cases where you need to know whether it was set explicitly or you are just 119 getting the default, you can use the `has\[NAME\]` property. If the value has 120 been set, and you want to clear it, you can set the `has\[NAME\]` to `NO`. 121 *proto3* syntax messages do away with this concept, thus the default values are 122 never included when the message is encoded. 123 124 The Objective C classes/enums can be used from Swift code. 125 126 Objective C Generator Options 127 ----------------------------- 128 129 **objc_class_prefix=\<prefix\>** (no default) 130 131 Since Objective C uses a global namespace for all of its classes, there can 132 be collisions. This option provides a prefix that will be added to the Enums 133 and Objects (for messages) generated from the proto. Convention is to base 134 the prefix on the package the proto is in. 135 136 Contributing 137 ------------ 138 139 Please make updates to the tests along with changes. If just changing the 140 runtime, the Xcode projects can be used to build and run tests. If your change 141 also requires changes to the generated code, 142 `objectivec/DevTools/full_mac_build.sh` can be used to easily rebuild and test 143 changes. Passing `-h` to the script will show the addition options that could 144 be useful. 145 146 Documentation 147 ------------- 148 149 The complete documentation for Protocol Buffers is available via the 150 web at: 151 152 https://developers.google.com/protocol-buffers/ 153
