QString and Android String are not comparable??

Gourmet

Sorry if it was already discussed but I never met this in Internet. I did not find this in Qt Bug report site. Please let me know if I missed something.

I call Java function like this:

bool res = QAndroidJniObject::callStaticMethod<jboolean>( PCpath, 
                           "setAccountName", "(Ljava/lang/String;)Z", 
                           QAndroidJniObject::fromString( QString("stringInJavaCode") ).object<jstring>() );
qWarning()<<res;

The PCpath is static const char* string with proper content. The java method looks like:

    public static boolean setAccountName( String accountName )
    {
        //accountName = "stringInJavaCode";
        if( accountName == "stringInJavaCode" ) // defenitely the same cause it was copy-pasted
        {
            DebugMessage("BUT IT IS TRUE!!!");
            return true;
        }
        return false;
    }

And the output:

 : (null):0 ((null)): false

Uncomment accountName assignment and it will print:

 : (null):0 ((null)): "BUT IT IS TRUE!!!"
 : (null):0 ((null)): true

When printing both strings in Java code they are look identically. No difference. I suppose there was left invisible character from QString - the trailing '\0'. Looks like a bug in QAndroidJniObject::fromString() - it must convert QString content clearly. If there is trailing '\0' then it must be removed. Java strings are not null terminated. Backward conversion must add trailing zero.

J.Hilk

@gourmet
interesting, it shouldn't

this is the fromString function

QJNIObjectPrivate QJNIObjectPrivate::fromString(const QString &string)
{
    QJNIEnvironmentPrivate env;
    jstring res = env->NewString(reinterpret_cast<const jchar*>(string.constData()),
                                        string.length());
    QJNIObjectPrivate obj(res);
    env->DeleteLocalRef(res);
    return obj;
}

QString::length returns the number of chars that excludes the 0 termination QString("Hello").length() == 5

what do you get, when you log the string and the length of the string on the Java side?

Gourmet

@j-hilk Of course length() function excludes trailing zero. This is not a visible character and it is not taken in QString comparison.

@j-hilk said in QString and Android String are not comparable??:

when you log the string and the length of the string on the Java side?

Prints equal sizes.

    public static boolean setAccountName( String accountName )
    {
        String line = "stringInJavaCode";
        if( accountName == line ) // defenitely the same cause it was copy-pasted
        {
            DebugMessage("BUT IT IS TRUE!!!");
            return true;
        }
        DebugMessage(accountName.length()+" "+line.length());
        return false;
    }

: (null):0 ((null)): "16 16"
: (null):0 ((null)): false

Gourmet

Sorry I have find workaround this bug. It stopped my development. I will post official bug report later but now I finish discuss it here.

J.Hilk

@gourmet

well, to investigate further I suggest the following:

public static boolean setAccountName( String accountName )
    {
        String line = "stringInJavaCode";
        
       int l1 = accountName.length();
       int l2 = line.length();
       int lmin = Math.min(l1, l2); 
  
        for (int i = 0; i < lmin; i++) { 
            int str1_ch = (int)str1.charAt(i); 
            int str2_ch = (int)str2.charAt(i); 

            if(str1_ch != str2_ch)
               //Diff at index i
            DebugMessage("Diff here");

        }
        if( accountName == line ) // defenitely the same cause it was copy-pasted
        {
            DebugMessage("BUT IT IS TRUE!!!");
            return true;
        }
        DebugMessage(accountName.length()+" "+line.length());
        return false;
    }

Actually, in Java, == tests for reference equality (wether they are the same object) and .equals() tests for value equality (wether they are logically equal)

// These two have the same value
new String("test").equals("test") // --> true 

// ... but they are not the same object
new String("test") == "test" // --> false 

// ... neither are these
new String("test") == new String("test") // --> false

I guess,
working as indented...

Gourmet

if( accountName.equals( line ) )

This works. Hmmm... No wonder I hate Java.