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.
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
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 actuallysubscribing to it:
__block unsigned subscriptions = 0; RACSignal *loggingSignal = [RACSignal createSignal:^ RACDisposable * (id<RACSubscriber> subscriber) { subscriptions++; [subscriber sendCompleted]; return nil; }]; // Does not output anything yet loggingSignal = [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,andcreate 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 II RACSequence *mapped = [letters map:^(NSString *value) { return [value stringByAppendingString:value]; }];
Filtering
The [-filter:][RACStream] method uses a block to test each value,including itinto 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 8 RACSequence *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 9 RACSequence *concatenated = [letters concat:numbers];
Flattening
The [-flatten][RACStream] operator is applied to a stream-of-streams,andcombines 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 9 RACSequence *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 understandinghow it works is important for [-flattenMap:][RACStream].
-flattenMap:
is used to transform each of a stream's values into a newstream. Then,all of the streams returned will be flattened down into a singlestream. 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 9 RACSequence *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 I RACSignal *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,thenstarting another,and only returning the second signal's values.
Merging
The [+merge:][RACSignal+Operations] method will forward the values from manysignals 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:
methodswill watch multiple signals for changes,and then send the latest values fromall 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 theinputs have sent at least one. In the example above,@"A"
was neverforwarded because numbers
had not sent a value yet.
Switching
The [-switchToLatest][RACSignal+Operations] operator is applied toa 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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