1.設置tetxField的內邊距
[textField setValue:[NSNumber numberWithInt:5] forKey:@"paddingTop"];//上
[textField setValue:[NSNumber numberWithInt:5] forKey:@"paddingLeft"];//左
[textField setValue:[NSNumber numberWithInt:5] forKey:@"paddingBottom"];//下
[textField setValue:[NSNumber numberWithInt:5] forKey:@"paddingRight"];//右
