什么是谓词? ios面试攻克篇（二）

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Cocoa 提供了一个类 NSPredicate 类，该类主要用于指定过滤器的条件，该对象可以准确的描述所需条件，对每个对象通过谓词进行筛选，判断是否与条件相匹配。谓词表示计算真值或假值的函数。

NSPredicate *predicate;
    predicate=[NSPredicatepredicateWithFormat:@"name=='Herbie'"];//用predicateWithFormat创建一个谓词，name作为键路径
   BOOL match=[predicateevaluateWithObject:car];//car作为接收对象,evaluateWithObject返回一个bool值。
    NSLog(@"%s",(match)?"YES":"NO");
  predicate = [NSPredicatepredicateWithFormat:@"engine.horsepower > 150"];
    NSArray *cars = [garage cars];
    for (Car *car in [garage cars]) {
        if ([predicate evaluateWithObject: car]) {
            NSLog (@"%@", car.name);
    }

遍历cars判断是否是真，然后输出。

predicate = [NSPredicatepredicateWithFormat:@"engine.horsepower > 150"];
    NSArray *results;
    results = [carsfilteredArrayUsingPredicate: predicate];//它将循环过滤数组内容，根据谓词计算每个对象的值，并将值为YES的对象累计到将被返回的新数组中。
    NSLog (@"%@", results);
filteredArrayUsingPredicate这个方法可以得到我们所需要的值。加上
   NSArray *names;
    names=[results valueForKey:@"name"];
    NSLog (@"%@", names);

就和上面的值一样。

NSMutableArray *carsCopy = [carsmutableCopy];
  [carsCopyfilterUsingPredicate: predicate];//filterUsingPredicate和NSMutableArray构成新数组。
  NSLog (@"%@", carsCopy);
predicate = [NSPredicatepredicateWithFormat:@"engine.horsepower > %d", 50];
results = [cars filteredArrayUsingPredicate: predicate];
NSLog (@"%@", results);
NSPredicate *predicateTemplate;
    NSDictionary *varDict;
    predicateTemplate = [NSPredicatepredicateWithFormat: @"engine.horsepower > $POWER"];//创建一个键/值字典来存储，这里$符号用于变量
    varDict = [NSDictionarydictionaryWithObjectsAndKeys:
               [NSNumbernumberWithInt: 150],@"POWER", nil];//@后面参数名
    predicate = [predicateTemplatepredicateWithSubstitutionVariables: varDict];
    results = [cars filteredArrayUsingPredicate: predicate];
    NSLog (@"%@", results);
  predicate = [NSPredicatepredicateWithFormat:
                @"(engine.horsepower > 50) AND (engine.horsepower < 200)"];//可以运用运算符
    results = [cars filteredArrayUsingPredicate: predicate];
    NSLog (@"oop %@", results);
    predicate = [NSPredicatepredicateWithFormat:
                @"engine.horsepower BETWEEN { 50, 200 }"];//这里可以运用between关键字。和上面效果一样
    results = [cars filteredArrayUsingPredicate: predicate];
    NSLog (@"%@", results);
    NSArray *betweens = [NSArray arrayWithObjects:
                         [NSNumbernumberWithInt: 50], [NSNumbernumberWithInt: 200],nil];
    predicate = [NSPredicatepredicateWithFormat: @"engine.horsepower BETWEEN %@", betweens];
    results = [cars filteredArrayUsingPredicate: predicate];
    NSLog (@"%@", results);
    predicateTemplate = [NSPredicatepredicateWithFormat:@"engine.horsepower BETWEEN $POWERS"];
    varDict = [NSDictionarydictionaryWithObjectsAndKeys: betweens, @"POWERS", nil];
    predicate = [predicateTemplatepredicateWithSubstitutionVariables: varDict];//用变量
    results = [cars filteredArrayUsingPredicate: predicate];
    NSLog (@"%@", results);
    predicate = [NSPredicatepredicateWithFormat:@"name < 'Newton'"];//不等号不仅可以用于数字，也可以用于字符串值。
    results = [cars filteredArrayUsingPredicate: predicate];
    NSLog (@"%@", [results valueForKey: @"name"]);
    predicate = [NSPredicatepredicateWithFormat:@"name IN { 'Herbie', 'Snugs', 'Badger', 'Flap' }"];//包含在其中用IN
    results = [cars filteredArrayUsingPredicate: predicate];
    NSLog (@"%@", [results valueForKey: @"name"]);
    predicate = [NSPredicatepredicateWithFormat:@"SELF.name IN { 'Herbie', 'Snugs', 'Badger', 'Flap' }"];//self关键字
    results = [cars filteredArrayUsingPredicate: predicate];
    NSLog (@"%@", [results valueForKey: @"name"]);
    names = [cars valueForKey: @"name"];
    predicate = [NSPredicatepredicateWithFormat:@"SELF IN { 'Herbie', 'Snugs', 'Badger', 'Flap' }"];//self关键字
    results = [namesfilteredArrayUsingPredicate: predicate];
    NSLog (@"%@", results);
    predicate = [NSPredicatepredicateWithFormat:@"name BEGINSWITH 'Bad'"];//字符串运算符BEGINSWITH,ENDSWITH,CONTAINS[c][d][cd]
    results = [cars filteredArrayUsingPredicate: predicate];
    NSLog (@"%@", results);

BEGINSWITH：检查某个字符串是否以另一个字符串开头。
ENDSWITH：检查某个字符串是否以另一个字符串结尾。
CONTAINS：检查某个字符串是否以另一个字符串内部。
[c]不区分大小写[d]不区分发音符号即没有重音符号[cd]既不区分大小写，又不区分发音符号。

代表通配符Like还接受[cd].下面所示↓

predicate = [NSPredicatepredicateWithFormat:@"name LIKE[cd] '*er*'"];//*
    results = [cars filteredArrayUsingPredicate: predicate];
    NSLog (@"%@", results);

只匹配一个字符并且还可以接受[cd].下面所示↓

predicate = [NSPredicatepredicateWithFormat:@"name LIKE[cd] '???er*'"];
    results = [cars filteredArrayUsingPredicate: predicate];
    NSLog (@"%@", results);

还可以使用MATCHES运算符。赋给该运算符一个正则表达式。

iOS 谓词（NSPredicate）的应用

Cocoa实际开发中可以是使用NSPredicate及其父类NSComparisonPredicate和NSCompoundPredicate.其风格类似于SQL查询语言和正则表达式的混合体，提供了具有表现力的，自然语言界面来定义一个集合被搜寻的逻辑条件。一般来说稍微操作过数据库基本上很容易理解其中的方法，至于使用的方法也很简单。如下代码是实现方法:

//  BIDValidateMgr.h
//  TongHuiShop
//  Created by eJiupi on 14-10-29.
#import <Foundation/Foundation.h>
@interface BIDValidateMgr : NSObject
//手机号码验证
+ (BOOL)validateMobile:(NSString *)mobile;
+ (BOOL)validateEmail:(NSString *)email;
//身份证号
+ (BOOL)validateIdentityCard: (NSString *)identityCard;
@end

BIDValidateMgr.m 实现代码；

//
//  BIDValidateMgr.m
//  TongHuiShop
//  Created by eJiupi on 14-10-29.
#import "BIDValidateMgr.h"
@implementation BIDValidateMgr
//手机号码验证
+ (BOOL)validateMobile:(NSString *)mobile
    //手机号以13， 15，18开头，八个 \d 数字字符
    NSString *phoneRegex = @"^((13[0-9])|(15[^4,\\D])|(18[0,0-9]))\\d{8}$";
    NSPredicate *phoneTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@",phoneRegex];
    return [phoneTest evaluateWithObject:mobile];
+ (BOOL)validateEmail:(NSString *)email
    NSString *emailRegex = @"[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}";
    NSPredicate *emailTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", emailRegex];
    return [emailTest evaluateWithObject:email];
//身份证号
+ (BOOL)validateIdentityCard: (NSString *)identityCard
    BOOL flag;
    if (identityCard.length <= 0) {
        flag = NO;
        return flag;