如何建立基于CocoaPods的ReactiveCocoa工程

ReactiveCocoa 和 CocoaPods 一样也是目前很流行的 能方便和提高效率的框架.

其实不光ios 学习任何一门语音最快最直接的方法就是上手. 如果单单是看看文档只能是走马观花得到一个感性认识罢了.前两天之前一个公司的测试人员跟我联系说如何学习JAVA,我问他是怎么学的,他说从网上下了好多视频教程,一直在看视频教程,也买了一些书. 我问他敲了多少代码,他说很少. 其实跟他一样的人不少. 我觉得任何事情都不简单,因为看起来简单的事情自己没有实际做过的话 往往会遇到各种各样的问题. 这也是为什么在工作中制定项目进度计划的时候 我尽量给自己和团队中的人多争取时间的最主要的一个因素.

好了,自己一些啰嗦和感悟. 下面开始正式.

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What is Reactive Cocoa?

RAV is an Object-C framework for Functional Reavtive Programming; 两个关键点: 1:framework 既然是framework 那就跟你用的其他framework没什么区别 无非就是加到工程中引用罢了.不做多余解释 2:Functional Reavtive Programming 实时响应式编程

虾米引用被阿里收购后现在先上的mac版本的虾米音乐就是用Reactive Cocoa开发的.用阿里人自己的话来说就是

好东西啊，以前我们用 KVO 或 Notification 来自动绑定数据，改用 ReactiveCocoa 写以后，代码结构更佳简单清晰，同时代码行数直接减少 60% 以上

来点直观的对比吧,比如我们想要实现一个需求:当变量中的字符串改变后即时做出相应的反馈 我们用KVO 需要如下这样做

// In your viewDidLoad/awakeFromNib/init[self addObserver:self        forKeyPath:@"someString"           options:NSKeyValueObservingOptionNew           context:&someStringChangeContext];// In dealloc[self removeObserver:self           forKeyPath:@"someString"              context:&someStringChangeContext];// Elsewhere in your class- (void)observeValueForKeyPath:(NSString *)keyPath                       ofObject:(id)object                         change:(NSDictionary *)change                        context:(void *)context{    if (context == &someStringChangeContext) {        if ([keyPath isEqualToString:@"someString"]) {                    // Do a bunch of stuff here        }    }}

上面一坨代码 在应用Reactive Cocoa后 只有短短一行

[RACObserve(self, someString) distinctUntilChanged] subscribeNext:^(NSString *string) {    // Do a bunch of things here, just like you would with KVO}];

开始动手

因为我之前安装了CocoaPods,所以我这次写的ReactiveCocoaDemo 是基于CocoaPods的.如果没有安装的可以童鞋,可以直接从github上下载ReactiveCocoa

前期工作:

1.打开xcode 创建一个工程,我命名的工程名为ReactiveCocoaDemo,

2.终端到工程路径下

cd ReactiveCocoaDemo/pod search ReactiveCocoa

3.配置依赖文件

vi Podfile    platform :ios,'5.0'    pod 'ReactiveCocoa'wq

4.下载文件

 pod install /update

5:打开"Build Phases" 选中相应的target, 添加 RAC 到 "Link Binary With Libraries".加上libReactiveCocoa-iOS.a

如下图

6:在Header Search Paths 中添加$(BUILD_ROOT)/../IntermediateBuildFilesPath/UninstalledProducts/include"

7:在 "Other Linker Flags" 添加 -ObjC

8:在ReactiveCocoaDemo-Prefix.pch 将RAC的头文件加进去

#import "ReactiveCocoa.h"

现在要实现如下功能

两个输入框 一个提示的Lable 一个按钮, 1.当两个输入框的内容相同时 提示文字显示"成功" 按钮可以点击 2.当任意一个输入框没有输入内容时 提示文字显示"请输入" 按钮不可点击 3.当输入框非空且两个输入内容不同时 提示"请重新输入" 按钮不可点击

下面是部分实现代码:

@weakify(self);[[RACObserve(self, warningText)  filter:^(NSString *newString) {      self.resultLabel.text = newString;      return YES;//          return [newString hasPrefix:@"Success"];  }] subscribeNext:^(NSString *newString) {     @strongify(self);     self.bt.enabled = [newString hasPrefix:@"Success"]; }];RAC(self,self.warningText) = [RACSignal combineLatest:@[RACObserve(self,self.input.text),RACObserve(self, self.verifyInput.text)]reduce:^(NSString *password, NSString *passwordConfirm){    if ([passwordConfirm isEqualToString:password])    {        return @"Success";    }    else if([password length] == 0 || [passwordConfirm length] ==0 )    {        return @"Please Input";    }    else    return @"Input Error";}  ];

对应关系如下图所示

学过C++ 的应该觉得这个很类似于Qt中的信号槽机制

需要说明的是 因为RAC很大程度上是依赖于Block的.所以在RAC前面我们加上@weakify(my_variable) 避免循环引用,然后在每一个 RAC块中为了防止提前释放我们需要用@strongify(my_variable)来对对象进行持有.详情点击

运行效果图如下

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文档附录

Subscription

The [-subscribe…][RACSignal] methods give you access to the current and future values in a signal:

RACSignal *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence.signal;// Outputs: A B C D[letters subscribeNext:^(NSString *x) {    NSLog(@"%@", x);}];

For a cold signal, side effects will be performed once per subscription:

__block unsigned subscriptions = 0;RACSignal *loggingSignal = [RACSignal createSignal:^ RACDisposable * (id<RACSubscriber> subscriber) {    subscriptions++;    [subscriber sendCompleted];    return nil;}];// Outputs:// subscription 1[loggingSignal subscribeCompleted:^{    NSLog(@"subscription %u", subscriptions);}];// Outputs:// subscription 2[loggingSignal subscribeCompleted:^{    NSLog(@"subscription %u", subscriptions);}];

This behavior can be changed using a [connection][Connections].

Injecting effects

The [-do…][RACSignal+Operations] methods add side effects to a signal without actually subscribing to it:

__block unsigned subscriptions = 0;RACSignal *loggingSignal = [RACSignal createSignal:^ RACDisposable * (id<RACSubscriber> subscriber) {    subscriptions++;    [subscriber sendCompleted];    return nil;}];// Does not output anything yetloggingSignal = [loggingSignal doCompleted:^{    NSLog(@"about to complete subscription %u", subscriptions);}];// Outputs:// about to complete subscription 1// subscription 1[loggingSignal subscribeCompleted:^{    NSLog(@"subscription %u", subscriptions);}];

Transforming streams

These operators transform a single stream into a new stream.

Mapping

The [-map:][RACStream] method is used to transform the values in a stream, and create a new stream with the results:

RACSequence *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence;// Contains: AA BB CC DD EE FF GG HH IIRACSequence *mapped = [letters map:^(NSString *value) {    return [value stringByAppendingString:value];}];

Filtering

The [-filter:][RACStream] method uses a block to test each value, including it into the resulting stream only if the test passes:

RACSequence *numbers = [@"1 2 3 4 5 6 7 8 9" componentsSeparatedByString:@" "].rac_sequence;// Contains: 2 4 6 8RACSequence *filtered = [numbers filter:^ BOOL (NSString *value) {    return (value.intValue % 2) == 0;}];

Combining streams

These operators combine multiple streams into a single new stream.

Concatenating

The [-concat:][RACStream] method appends one stream's values to another:

RACSequence *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence;RACSequence *numbers = [@"1 2 3 4 5 6 7 8 9" componentsSeparatedByString:@" "].rac_sequence;// Contains: A B C D E F G H I 1 2 3 4 5 6 7 8 9RACSequence *concatenated = [letters concat:numbers];

Flattening

The [-flatten][RACStream] operator is applied to a stream-of-streams, and combines their values into a single new stream.

Sequences are concatenated:

RACSequence *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence;RACSequence *numbers = [@"1 2 3 4 5 6 7 8 9" componentsSeparatedByString:@" "].rac_sequence;RACSequence *sequenceOfSequences = @[ letters, numbers ].rac_sequence;// Contains: A B C D E F G H I 1 2 3 4 5 6 7 8 9RACSequence *flattened = [sequenceOfSequences flatten];

Signals are merged:

RACSubject *letters = [RACSubject subject];RACSubject *numbers = [RACSubject subject];RACSignal *signalOfSignals = [RACSignal createSignal:^ RACDisposable * (id<RACSubscriber> subscriber) {    [subscriber sendNext:letters];    [subscriber sendNext:numbers];    [subscriber sendCompleted];    return nil;}];RACSignal *flattened = [signalOfSignals flatten];// Outputs: A 1 B C 2[flattened subscribeNext:^(NSString *x) {    NSLog(@"%@", x);}];[letters sendNext:@"A"];[numbers sendNext:@"1"];[letters sendNext:@"B"];[letters sendNext:@"C"];[numbers sendNext:@"2"];

Mapping and flattening

Flattening isn't that interesting on its own, but understanding how it works is important for [-flattenMap:][RACStream].

-flattenMap:is used to transform each of a stream's values into a new stream. Then, all of the streams returned will be flattened down into a single stream. In other words, it's -map: followed by -flatten.

This can be used to extend or edit sequences:

RACSequence *numbers = [@"1 2 3 4 5 6 7 8 9" componentsSeparatedByString:@" "].rac_sequence;// Contains: 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9RACSequence *extended = [numbers flattenMap:^(NSString *num) {    return @[ num, num ].rac_sequence;}];// Contains: 1_ 3_ 5_ 7_ 9_RACSequence *edited = [numbers flattenMap:^(NSString *num) {    if (num.intValue % 2 == 0) {        return [RACSequence empty];    } else {        NSString *newNum = [num stringByAppendingString:@"_"];        return [RACSequence return:newNum];     }}];

Or create multiple signals of work which are automatically recombined:

RACSignal *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence.signal;[[letters    flattenMap:^(NSString *letter) {        return [database saveEntriesForLetter:letter];    }]    subscribeCompleted:^{        NSLog(@"All database entries saved successfully.");    }];

Combining signals

These operators combine multiple signals into a single new [RACSignal][].

Sequencing

[-then:][RACSignal+Operations] starts the original signal, waits for it to complete, and then only forwards the values from a new signal:

RACSignal *letters = [@"A B C D E F G H I" componentsSeparatedByString:@" "].rac_sequence.signal;// The new signal only contains: 1 2 3 4 5 6 7 8 9//// But when subscribed to, it also outputs: A B C D E F G H IRACSignal *sequenced = [[letters    doNext:^(NSString *letter) {        NSLog(@"%@", letter);    }]    then:^{        return [@"1 2 3 4 5 6 7 8 9" componentsSeparatedByString:@" "].rac_sequence.signal;    }];

This is most useful for executing all the side effects of one signal, then starting another, and only returning the second signal's values.

Merging

The [+merge:][RACSignal+Operations] method will forward the values from many signals into a single stream, as soon as those values arrive:

RACSubject *letters = [RACSubject subject];RACSubject *numbers = [RACSubject subject];RACSignal *merged = [RACSignal merge:@[ letters, numbers ]];// Outputs: A 1 B C 2[merged subscribeNext:^(NSString *x) {    NSLog(@"%@", x);}];[letters sendNext:@"A"];[numbers sendNext:@"1"];[letters sendNext:@"B"];[letters sendNext:@"C"];[numbers sendNext:@"2"];

Combining latest values

The [+combineLatest:][RACSignal+Operations] and+combineLatest:reduce:methods will watch multiple signals for changes, and then send the latest values from all of them when a change occurs:

RACSubject *letters = [RACSubject subject];RACSubject *numbers = [RACSubject subject];RACSignal *combined = [RACSignal    combineLatest:@[ letters, numbers ]    reduce:^(NSString *letter, NSString *number) {        return [letter stringByAppendingString:number];    }];// Outputs: B1 B2 C2 C3[combined subscribeNext:^(id x) {    NSLog(@"%@", x);}];[letters sendNext:@"A"];[letters sendNext:@"B"];[numbers sendNext:@"1"];[numbers sendNext:@"2"];[letters sendNext:@"C"];[numbers sendNext:@"3"];

Note that the combined signal will only send its first value when all of the inputs have sent at least one. In the example above,@"A"was never forwarded becausenumbershad not sent a value yet.

Switching

The [-switchToLatest][RACSignal+Operations] operator is applied to a signal-of-signals, and always forwards the values from the latest signal:

RACSubject *letters = [RACSubject subject];RACSubject *numbers = [RACSubject subject];RACSubject *signalOfSignals = [RACSubject subject];RACSignal *switched = [signalOfSignals switchToLatest];// Outputs: A B 1 D[switched subscribeNext:^(NSString *x) {    NSLog(@"%@", x);}];[signalOfSignals sendNext:letters];[letters sendNext:@"A"];[letters sendNext:@"B"];[signalOfSignals sendNext:numbers];[letters sendNext:@"C"];[numbers sendNext:@"1"];[signalOfSignals sendNext:letters];[numbers sendNext:@"2"];[letters sendNext:@"D"];

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