iOS UITextField 设置内边距
[self.yourTextField setValue:[NSNumber numberWithInt:5] forKey:@"_paddingTop"];
[self.yourTextField setValue:[NSNumber numberWithInt:5] forKey:@"_paddingLeft"];
[self.yourTextField setValue:[NSNumber numberWithInt:5] forKey:@"_paddingBottom"];
[self.yourTextField setValue:[NSNumber numberWithInt:5] forKey:@"_paddingRight"];