谓语用NSPredicate对象来代表三个子类：
NSCompoundPredicate NSCompoundPredicate和NSExpression
//FKUser是一个自定义的类，包含Name和pass两个属性
NSPredicate* pred=[NSPredicate predicateWithFormat:
@"name like 's*'"];
FKUser* user1=[[FKUser alloc]initWithName:@"sum" pass:@"123"];
BOOL reslult1=[pred evaluateWithObject:
user1];
NSLog(@"user1的name是否以s开头:%d",reslult1);
FKUser* user2=[[FKUser alloc]initWithName:@"bai" pass:@"321"];
BOOL result2=[pred evaluateWithObject:user2];
NSLog(@"user2的name是否以s开头:%d",result2);
NSMutableArray* arr2=[[NSMutableArray alloc] initWithObjects:
@2,@20,@40,@30,@15, nil];
NSPredicate* pred1=[NSPredicate predicateWithFormat:@"self>20"];
[arr2 filterUsingPredicate:
pred1];
NSLog(@"%@",arr2);
NSSet* set=[NSSet setWithObjects:
[[FKUser alloc] initWithName:@"孙悟空" pass:@"123"],
[[FKUser alloc]initWithName:
@"金角大王"pass:@"321"],nil];
NSPredicate* pred2=[NSPredicate predicateWithFormat:
@"name CONTAINS '大王'"];
NSSet* newSet=[set filteredSetUsingPredicate:
pred2];
NSLog(@"%@",newSet);
7.9.3 在谓语中使用占位符参数
1.%K 动态传入属性名
2、%@ 动态设置属性名
如果使用了形如￥SUBSTR的占位符，传入参数：
1、县调用NSPredicate的predicateWithSubstitutionVariables:方法为占位符参数设置参数值，该方法返回一个可用的NSPredicate对象
2.直接调用NSPredicate的evaluateWithObject:substitutionVariables:方法同时完成参数设置和计算结果
NSPredicate* predTemplate=[NSPredicate predicateWithFormat:@"%K contains $SUBSTR",@"pass"];
NSPredicate* pred4=[predTemplate predicateWithSubstitutionVariables:[NSDictionary dictionaryWithObjectsAndKeys:@"123",@"SUBSTR", nil]];
NSSet* newSet3=[set filteredSetUsingPredicate:pred4];
NSLog(@"%@",newSet3);
