- Cocoa用NSPredicate描述查詢的方式,原理類似於在數據庫中進行查詢
- 計算謂詞:
- //基本的查詢
- NSPredicate *predicate;
- predicate = [NSPredicate predicateWithFormat: @"name == 'Herbie'"];
- BOOL match = [predicate evaluateWithObject: car];
- NSLog (@"%s", (match) ? "YES" : "NO");
- //在整個cars裏面循環比較
- predicate = [NSPredicate predicateWithFormat: @"engine.horsepower > 150"];
- NSArray *cars = [garage cars];
- for (Car *car in [garage cars]) {
- if ([predicate evaluateWithObject: car]) {
- NSLog (@"%@", car.name);
- }
- }
- //輸出完整的信息
- predicate = [NSPredicate predicateWithFormat: @"engine.horsepower > 150"];
- NSArray *results;
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", results);
- //含有變量的謂詞
- NSPredicate *predicateTemplate = [NSPredicate predicateWithFormat:@"name == $NAME"];
- NSDictionary *varDict;
- varDict = [NSDictionary dictionaryWithObjectsAndKeys:
- @"Herbie", @"NAME", nil];
- predicate = [predicateTemplate predicateWithSubstitutionVariables: varDict];
- NSLog(@"SNORGLE: %@", predicate);
- match = [predicate evaluateWithObject: car];
- NSLog (@"%s", (match) ? "YES" : "NO");
- //注意不能使用$VARIABLE作爲路徑名,因爲它值代表值
- //謂詞字符竄還支持c語言中一些常用的運算符
- predicate = [NSPredicate predicateWithFormat:
- @"(engine.horsepower > 50) AND (engine.horsepower < 200)"];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"oop %@", results);
- predicate = [NSPredicate predicateWithFormat: @"name < 'Newton'"];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", [results valueForKey: @"name"]);
- //強大的數組運算符
- predicate = [NSPredicate predicateWithFormat:
- @"engine.horsepower BETWEEN { 50, 200 }"];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", results);
- NSArray *betweens = [NSArray arrayWithObjects:
- [NSNumber numberWithInt: 50], [NSNumber numberWithInt: 200], nil];
- predicate = [NSPredicate predicateWithFormat: @"engine.horsepower BETWEEN %@", betweens];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", results);
- predicateTemplate = [NSPredicate predicateWithFormat: @"engine.horsepower BETWEEN $POWERS"];
- varDict = [NSDictionary dictionaryWithObjectsAndKeys: betweens, @"POWERS", nil];
- predicate = [predicateTemplate predicateWithSubstitutionVariables: varDict];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", results);
- //IN運算符
- predicate = [NSPredicate predicateWithFormat: @"name IN { 'Herbie', 'Snugs', 'Badger', 'Flap' }"];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", [results valueForKey: @"name"]);
- predicate = [NSPredicate predicateWithFormat: @"SELF.name IN { 'Herbie', 'Snugs', 'Badger', 'Flap' }"];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", [results valueForKey: @"name"]);
- names = [cars valueForKey: @"name"];
- predicate = [NSPredicate predicateWithFormat: @"SELF IN { 'Herbie', 'Snugs', 'Badger', 'Flap' }"];
- results = [names filteredArrayUsingPredicate: predicate];//這裏限制了SELF的範圍
- NSLog (@"%@", results);
- //BEGINSWITH,ENDSWITH,CONTAINS
- //附加符號,[c],[d],[cd],c表示不區分大小寫,d表示不區分發音字符,cd表示什麼都不區分
- predicate = [NSPredicate predicateWithFormat: @"name BEGINSWITH 'Bad'"];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", results);
- predicate = [NSPredicate predicateWithFormat: @"name BEGINSWITH 'HERB'"];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", results);
- predicate = [NSPredicate predicateWithFormat: @"name BEGINSWITH[cd] 'HERB'"];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", results);
- //LIKE運算符(通配符)
- predicate = [NSPredicate predicateWithFormat: @"name LIKE[cd] '*er*'"];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", results);
- predicate = [NSPredicate predicateWithFormat: @"name LIKE[cd] '???er*'"];
- results = [cars filteredArrayUsingPredicate: predicate];
- NSLog (@"%@", results);
NSPredicate過濾器 用法
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