CRASH: -[NSNull length]: unrecognized selector sent to instance錯誤的處理辦法

開發中從後臺請求數據，返回如下：

2014-12-05 16:44:52.535 掌麥[6984:613] getDefaultAddress: reuslt == {
    item =     {
        data =         {
            address = "<null>";
            area = "<null>";
            city = "<null>";
            name = "";
            phone = 18503051318;
            province = "<null>";
        };
        mark = 1;
        msg = "\U6210\U529f";
    };
    status = 1;
}

我直接解析出字典dic，賦值：

<span style="font-size:18px;">    NSString *address = [dic objectForKey:@"address"];
    //NSString *area = [dic objectForKey:@"area"];
    NSString *name = [dic objectForKey:@"name"];
    //NSString *city = [dic objectForKey:@"city"];
    NSString *phone = [dic objectForKey:@"phone"];
    //NSString *province = [dic objectForKey:@"province"];
    self.addressLabel.text = address;
    self.nameLabel.text    = name;
    self.phoneLabel.text   = phone;

</span>

   結果報錯：CRASH: -[NSNull length]: unrecognized selector sent to instance

原因及時後臺返回有些值爲null，在object－c中就是nsull的空值

所以解析後，應加一判斷，防止出錯

<span style="font-size:18px;">    if (![address isKindOfClass:[NSNull class]]) {
        self.addressLabel.text = address;
    }
    if (![name isKindOfClass:[NSNull class]]) {
        self.nameLabel.text    = name;
    }
    if (![phone isKindOfClass:[NSNull class]]) {
        self.phoneLabel.text   = phone;
    }
</span>

這樣就OK了