@interface User : NSObject    @property (nonatomic,retain) NSString* tRetain;  @property (nonatomic,assign) NSString* tAssign;  @property (nonatomic,copy) NSString* tcopy;    @end

类User有个属性tRetain, 只是就用NSString类型了（此类型一般用copy, 因为可能是个NSMutableString,不希望在赋值后被其他地方修改内容）。

User* user = [[User alloc]init];    NSString* testRetain = [NSString stringWithFormat:@"retain"];  NSLog(@"testRetain.retainCount=%lu",(unsigned long)testRetain.retainCount);  //1    user.tRetain = testRetain;  NSLog(@"testRetain.retainCount=%lu",(unsigned long)testRetain.retainCount);   //2  NSLog(@"user.tRetain.retainCount=%lu",(unsigned long)user.tRetain.retainCount); //2    NSString* testRetain2 = @"retain2";  NSLog(@"testRetain2.retainCount=%lu",(unsigned long)testRetain2.retainCount); //4294967295 自动释放对象  返回max unsigned long      user.tRetain = testRetain2;  NSLog(@"testRetain.retainCount=%lu",(unsigned long)testRetain.retainCount);   //1  NSLog(@"testRetain2.retainCount=%lu",(unsigned long)testRetain2.retainCount); //4294967295  NSLog(@"user.RetainValue.retainCount=%lu",(unsigned long)user.tRetain.retainCount); //4294967295      NSString* testRetain3 = [NSString stringWithFormat: @"retain3"];  NSLog(@"testRetain3.retainCount=%lu",(unsigned long)testRetain3.retainCount); //1    [testRetain3 retain];  NSLog(@"testRetain3.retainCount=%lu",(unsigned long)testRetain3.retainCount); //2    NSString* testRetain4 = [NSString stringWithString:testRetain3];  NSLog(@"testRetain3.retainCount=%lu",(unsigned long)testRetain3.retainCount); //3  NSLog(@"testRetain4.retainCount=%lu",(unsigned long)testRetain4.retainCount); //3

strong是ARC后引入的关键字， 在ARC环境中等同于Retain。

 

NSSring* str = [NSString stringWithString:字符串]；   此方法相当于上文对一个retain属性赋值。   若后面的字符串参数的计数为4294967295，则str的计数也是。   若字符串参数可计数， 例如1， 则执行后计数加1.