153 lines
5.7 KiB
Markdown
153 lines
5.7 KiB
Markdown
Protocol Buffers - Google's data interchange format
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===================================================
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[](https://travis-ci.org/google/protobuf)
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Copyright 2008 Google Inc.
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This directory contains the Objective C Protocol Buffers runtime library.
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Requirements
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------------
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The Objective C implementation requires:
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- Objective C 2.0 Runtime (32bit & 64bit iOS, 64bit OS X).
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- Xcode 7.0 (or later).
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- The library code does *not* use ARC (for performance reasons), but it all can
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be called from ARC code.
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Installation
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------------
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The full distribution pulled from github includes the sources for both the
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compiler (protoc) and the runtime (this directory). To build the compiler
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and run the runtime tests, you can use:
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$ objectivec/DevTools/full_mac_build.sh
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This will generate the `src/protoc` binary.
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Building
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--------
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There are two ways to include the Runtime sources in your project:
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Add `objectivec/\*.h` & `objectivec/GPBProtocolBuffers.m` to your project.
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*or*
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Add `objectivec/\*.h` & `objectivec/\*.m` except for
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`objectivec/GPBProtocolBuffers.m` to your project.
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If the target is using ARC, remember to turn off ARC (`-fno-objc-arc`) for the
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`.m` files.
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The files generated by `protoc` for the `*.proto` files (`\*.pbobjc.h' and
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`\*.pbobjc.m`) are then also added to the target.
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Usage
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-----
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The objects generated for messages should work like any other Objective C
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object. They are mutable objects, but if you don't change them, they are safe
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to share between threads (similar to passing an NSMutableDictionary between
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threads/queues; as long as no one mutates it, things are fine).
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There are a few behaviors worth calling out:
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A property that is type NSString\* will never return nil. If the value is
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unset, it will return an empty string (@""). This is inpart to align things
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with the Protocol Buffers spec which says the default for strings is an empty
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string, but also so you can always safely pass them to isEqual:/compare:, etc.
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and have deterministic results.
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A property that is type NSData\* also won't return nil, it will return an empty
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data ([NSData data]). The reasoning is the same as for NSString not returning
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nil.
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A property that is another GPBMessage class also will not return nil. If the
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field wasn't already set, you will get a instance of the correct class. This
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instance will be a temporary instance unless you mutate it, at which point it
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will be attached to its parent object. We call this pattern *autocreators*.
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Similar to NSString and NSData properties it makes things a little safer when
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using them with isEqual:/etc.; but more importantly, this allows you to write
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code that uses Objective C's property dot notation to walk into nested objects
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and access and/or assign things without having to check that they are not nil
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and create them each step along the way. You can write this:
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```
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- (void)updateRecord:(MyMessage *)msg {
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...
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// Note: You don't have to check subMessage and otherMessage for nil and
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// alloc/init/assign them back along the way.
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msg.subMessage.otherMessage.lastName = @"Smith";
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...
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}
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```
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If you want to check if a GPBMessage property is present, there is always as
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`has\[NAME\]` property to go with the main property to check if it is set.
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A property that is of an Array or Dictionary type also provides *autocreator*
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behavior and will never return nil. This provides all the same benefits you
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see for the message properties. Again, you can write:
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```
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- (void)updateRecord:(MyMessage *)msg {
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...
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// Note: Just like above, you don't have to check subMessage and otherMessage
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// for nil and alloc/init/assign them back along the way. You also don't have
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// to create the siblingsArray, you can safely just append to it.
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[msg.subMessage.otherMessage.siblingsArray addObject:@"Pat"];
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...
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}
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```
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If you are inspecting a message you got from some other place (server, disk,
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etc), you may want to check if the Array or Dictionary has entries without
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causing it to be created for you. For this, there is always a `\[NAME\]_Count`
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property also provided that can return zero or the real count, but won't trigger
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the creation.
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For primitive type fields (ints, floats, bools, enum) in messages defined in a
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`.proto` file that use *proto2* syntax there are conceptual differences between
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having an *explicit* and *default* value. You can always get the value of the
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property. In the case that it hasn't been set you will get the default. In
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cases where you need to know whether it was set explicitly or you are just
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getting the default, you can use the `has\[NAME\]` property. If the value has
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been set, and you want to clear it, you can set the `has\[NAME\]` to `NO`.
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*proto3* syntax messages do away with this concept, thus the default values are
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never included when the message is encoded.
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The Objective C classes/enums can be used from Swift code.
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Objective C Generator Options
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-----------------------------
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**objc_class_prefix=\<prefix\>** (no default)
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Since Objective C uses a global namespace for all of its classes, there can
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be collisions. This option provides a prefix that will be added to the Enums
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and Objects (for messages) generated from the proto. Convention is to base
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the prefix on the package the proto is in.
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Contributing
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------------
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Please make updates to the tests along with changes. If just changing the
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runtime, the Xcode projects can be used to build and run tests. If your change
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also requires changes to the generated code,
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`objectivec/DevTools/full_mac_build.sh` can be used to easily rebuild and test
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changes. Passing `-h` to the script will show the addition options that could
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be useful.
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Documentation
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-------------
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The complete documentation for Protocol Buffers is available via the
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web at:
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https://developers.google.com/protocol-buffers/
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