JSON对象转NSData再转回后NSNumber值变更问题求助

Let's figure out why your price value (originally set to 106 as an NSNumber) is getting altered when you serialize your dictionary to NSData and deserialize it back to a JSON object. Below are the most common causes and actionable fixes to resolve this issue:

Common Causes & Fixes #

1. Accidental Floating-Point Conversion #

JSON doesn’t natively distinguish between integers and floats. When NSJSONSerialization deserializes numeric values, it returns NSNumber instances—but if your original price was stored as a float (e.g., @(106.0) instead of @106), deserialization might keep it as a float. While 106.0 represents the same value, this could look like a "change" if you’re expecting an integer type. In rare cases, floating-point precision errors might skew the value (though this is unlikely with a small integer like 106).

Fix:
Initialize the price explicitly as an integer to avoid ambiguity:

// Correct integer initialization for price
paramDict[@"storeInfo"][@"qrCodeInfo"][@"price"] = @106; 
// Or use [NSNumber numberWithInteger:106]; for older syntax

When deserializing, explicitly cast back to an integer type to eliminate any floating-point confusion:

NSDictionary *deserializedDict = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];
NSInteger price = [deserializedDict[@"storeInfo"][@"qrCodeInfo"][@"price"] integerValue];
// This will reliably return 106, even if the NSNumber is stored as a float

2. Unhandled Serialization/Deserialization Errors #

You’re passing nil for the error parameter in both serialization and deserialization calls. If there’s a hidden error (like invalid types in your dictionary), the resulting NSData could be malformed, leading to incorrect values when deserialized.

Fix:
Always check for errors to catch issues early:

// Serialization with error checking
NSError *serializationError = nil;
NSData *data = [NSJSONSerialization dataWithJSONObject:paramDict options:kNilOptions error:&serializationError];
if (serializationError) {
    NSLog(@"Serialization failed: %@", serializationError.localizedDescription);
    // Handle the error (e.g., fix invalid dictionary entries)
}

// Deserialization with error checking
NSError *deserializationError = nil;
NSDictionary *deserializedDict = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&deserializationError];
if (deserializationError) {
    NSLog(@"Deserialization failed: %@", deserializationError.localizedDescription);
    // Handle the error (e.g., check for corrupted data)
}

3. Unexpected Type in the Original Dictionary #

Double-check that the price value in your original paramDict is actually an NSNumber. If you accidentally stored it as a string (e.g., @"106"), deserialization will keep it as a string, which might look like a value change if you’re expecting a number.

Fix:
Validate the type before serialization to catch mismatches:

id priceValue = paramDict[@"storeInfo"][@"qrCodeInfo"][@"price"];
if ([priceValue isKindOfClass:[NSNumber class]]) {
    NSLog(@"Price is a valid NSNumber: %@", priceValue);
} else {
    NSLog(@"Unexpected type for price: %@", [priceValue class]);
    // Correct the type here (e.g., convert string to NSNumber)
}

4. Quick Test to Isolate the Issue #

Run this minimal test with your exact dictionary structure to verify if the round-trip works as expected. If this test outputs correct values, the problem is likely in how you’re building your original paramDict elsewhere in your code:

// Build your exact dictionary
NSDictionary *paramDict = @{
    @"channelId": @201,
    @"lang": @"EN",
    @"reqRefNo": @"vZRIzNd",
    @"storeInfo": @{
        @"clientInfo": @{
            @"deviceId": @"XXXXXXXXA67F488B836D19D80EC4FD8D"
        },
        @"loginLogId": @"XXXXXXXX5CAD4A0DA06BE2F055929856",
        @"qrCodeInfo": @{
            @"itemDesc": @"",
            @"itemName": @"hahsj",
            @"price": @106
        },
        @"userInfo": @{
            @"storeId": @3252
        }
    }
};

// Serialize
NSError *error = nil;
NSData *data = [NSJSONSerialization dataWithJSONObject:paramDict options:kNilOptions error:&error];
if (error) {
    NSLog(@"Serialize error: %@", error);
    return;
}

// Deserialize
NSDictionary *deserialized = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
if (error) {
    NSLog(@"Deserialize error: %@", error);
    return;
}

// Verify price
NSNumber *price = deserialized[@"storeInfo"][@"qrCodeInfo"][@"price"];
NSLog(@"Original price: %@ | Deserialized price: %@ | Integer value: %ld", @106, price, (long)[price integerValue]);

内容的提问来源于stack exchange，提问作者Sanket_B