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然后在.m文件中有,如下所示:
- (NSString *)preview { if ([self.body length] < 200) { _preview = self.body; } else { _preview = [self.body substringWithRange:NSMakeRange(0, 200)]; } return _preview; }
看起来像是:
- (NSString *)preview { [self willAccessValueForKey:@"preview"]; NSString *preview = [self primitiveValueForKey:@"preview"]; [self didAccessValueForKey:@"preview"]; if (preview == nil) { if ([self.body length] < 200) { preview = self.body; } else { preview = [self.body substringWithRange:NSMakeRange(0, 200)]; } [self setPrimitiveValue:preview forKey:@"preview"]; } return preview; }