For Loop和Array的问题

Question

以下方法代码是FOR循环，它从SQLite数据库构建26个数组（每个字母表一个字母）。

问题是名为MultipleArray的返回数组只返回16个数组，而不是应该返回25个数组。谁能发现为什么它没有返回完整的25个阵列？

编辑 - 问题似乎是因为字母Q在数据库中没有数据（这是正确的）数组17（字母Q）没有内容。构建mulptipleArray的语句然后在此时终止添加数组。有谁知道如何解决这个问题？

谢谢。

- (NSMutableArray *)placesInfo {

NSString *tmpLike = [[NSString alloc] init];
multipleArray = [[NSMutableArray alloc] init];

for (int i = 0; i < 26; i++) {

    NSMutableArray *retval = [[[NSMutableArray alloc] init] autorelease];
    tmpLike = @"";

    switch (i) {
        case 0:
            tmpLike = @"A";
            break;
        case 1:
            tmpLike = @"B";
            break;
        case 2:
            tmpLike = @"C";
            break;
        case 3:
            tmpLike = @"D";
            break;
        case 4:
            tmpLike = @"E";
            break;
        case 5:
            tmpLike = @"F";
            break;
        case 6:
            tmpLike = @"G";
            break;
        case 7:
            tmpLike = @"H";
            break;
        case 8:
            tmpLike = @"I";
            break;
        case 9:
            tmpLike = @"J";
            break;
        case 10:
            tmpLike = @"K";
            break;
        case 11:
            tmpLike = @"L";
            break;
        case 12:
            tmpLike = @"M";
            break;
        case 13:
            tmpLike= @"N";
            break;
        case 14:
            tmpLike = @"O";
            break;
        case 15:
            tmpLike = @"P";
            break;
        case 16:
            tmpLike = @"Q";
            break;
        case 17:
            tmpLike = @"R";
            break;
        case 18:
            tmpLike = @"S";
            break;
        case 19:
            tmpLike = @"T";
            break;
        case 20:
            tmpLike = @"U";
            break;
        case 21:
            tmpLike = @"V";
            break;
        case 22:
            tmpLike = @"W";
            break;
        case 23:
            tmpLike = @"X";
            break;
        case 24:
            tmpLike = @"Y";
            break;
        case 25:
            tmpLike = @"Z";
            break;
        default:
            break;
    }  

NSString *query = [[NSString alloc] initWithFormat: @"SELECT Name, Description, Postcode, AddressLine1, ImageURL, Free, Area, OpeningTimes, NearestTube, Cost,UniqueID, URL, Number, FirstLetter FROM MainDetails WHERE FirstLetter = '%@%'",tmpLike];

sqlite3_stmt *statement;
if (sqlite3_prepare_v2(_database, [query UTF8String], -1, &statement, nil) 
    == SQLITE_OK) {
    while (sqlite3_step(statement) == SQLITE_ROW) {

        char *nameChars = (char *) sqlite3_column_text(statement, 0);
        char *desChars = (char *) sqlite3_column_text(statement, 1);
        char *postChars = (char *) sqlite3_column_text(statement, 2);
        char *addyChars = (char *) sqlite3_column_text(statement, 3);
        char *imageChars = (char *) sqlite3_column_text(statement, 4);
        char *freeChars = (char *) sqlite3_column_text(statement, 5);
        char *areaChars = (char *) sqlite3_column_text(statement, 6);
        char *openChars = (char *) sqlite3_column_text(statement, 7);
        char *nearChars = (char *) sqlite3_column_text(statement, 8);
        char *costChars = (char *) sqlite3_column_text(statement, 9);
        int uniqueID = sqlite3_column_int(statement, 10);
        char *urlChars = (char *) sqlite3_column_text(statement, 11);
        char *numberChars = (char *) sqlite3_column_text(statement, 12);

        NSString *name = [[NSString alloc] initWithUTF8String:nameChars];
        NSString *description = [[NSString alloc] initWithUTF8String:desChars];
        NSString *postcode = [[NSString alloc] initWithUTF8String:postChars];
        NSString *address = [[NSString alloc] initWithUTF8String:addyChars];
        NSString *image = [[NSString alloc] initWithUTF8String:imageChars];
        NSString *free = [[NSString alloc] initWithUTF8String:freeChars];
        NSString *area = [[NSString alloc] initWithUTF8String:areaChars];
        NSString *openT = [[NSString alloc] initWithUTF8String:openChars];
        NSString *near = [[NSString alloc] initWithUTF8String:nearChars];
        NSString *cost = [[NSString alloc] initWithUTF8String:costChars];
        NSString *url = [[NSString alloc] initWithUTF8String:urlChars];
        NSString *number = [[NSString alloc] initWithUTF8String:numberChars];

        PlaceObject *info = [[PlaceObject alloc] 
                             initWithUniqueID: uniqueID name : name description:description postCode:postcode addressOne : address image:image free:free area:area openingTimes:openT nearestTube:near cost:cost url:url number:number];


        [retval addObject:info];

        int x= [retval count];

        NSLog(@"%d",i);

        if (x ==0) {

            NSLog(@"No content");
        }


    switch (i) {
            case 0:
            letterA = retval;
            break;
            case 1:
            letterB = retval;
            break;
            case 2:
                letterC = retval;
                break;
            case 3:
                letterD = retval;
                break;
            case 4:
                letterE = retval;
                break;
            case 5:
                letterF = retval;
                break;
            case 6:
                letterG = retval;
                break;
            case 7:
                letterH = retval;
                break;
            case 8:
                letterI = retval;
                break;
            case 9:
                letterJ = retval;
                break;
            case 10:
                letterK = retval;
                break;
            case 11:
                letterL = retval;
                break;
            case 12:
                letterM = retval;
                break;
            case 13:
                letterN = retval;
                break;
            case 14:
                letterO = retval;
                break;
            case 15:
                letterP = retval;
                break;
            case 16:
                letterQ = retval;
                break;
            case 17:
                letterR = retval;
                break;
            case 18:
                letterS = retval;
                break;
            case 19:
                letterT = retval;
                break;
            case 20:
                letterU = retval;
            break;
            case 21:
                letterV = retval;
                break;
            case 22:
                letterW = retval;
                break;
            case 23:
                letterX = retval;
            break;
            case 24:
                letterY = retval;
                break;
            case 25:
                letterZ = retval;
                break;
        default:
            break;                    
    } 
        [name release];
        query = @"";
        [query release];
        [description release];
        [url release];
        [number release];
        [postcode release];
        [address release];
        [image release];
        [free release];
        [area release];
        [openT release];
        [near release];
        [cost release];
        [info release];
    }
    sqlite3_finalize(statement);
}

}

tmpLike = @"";
[tmpLike release];

multipleArray = [NSMutableArray arrayWithObjects: letterA, letterB, letterC, letterD, letterE, letterF, letterG, letterH, letterI, letterJ, letterK, letterL, letterM, letterN, letterO,letterP, letterQ, letterR, letterS, letterT, letterU, letterV, letterW, letterX, letterY, letterZ, nil];  

int x= [multipleArray count];
NSLog(@"Mulptilpe Array Contents: %d", x);
NSLog(@"%@",multipleArray);
return multipleArray;
}

Answer 1

  

编辑 - 问题似乎是因为字母Q在数据库中没有数据（这是正确的）数组17（字母Q）没有内容。构建mulptipleArray的语句然后在此时终止添加数组。有谁知道如何解决这个问题？

如果您需要在数组中插入nil值，请使用[NSNull null]。这个价值没有什么神奇之处。它只是一个你可以在以后测试的对象。您无法将真实nil插入NSMutableArray。

Answer 2

我首先要简化你的代码。两个大的switch语句是不必要的。 您可以通过删除tmpLike变量并替换它来删除第一个 查询字符串：

NSString *query = [[NSString alloc] initWithFormat: @"SELECT ...blah blah blah... WHERE FirstLetter = '%c%'", 'A' + i];

我认为字母A ... letterZ是NSMutableArray在其他地方宣布的。你可以摆脱第二个switch语句 只需将letter*添加到retval。

，即可填充所有multipleArray数组

[multipleArray addObject:retval]

这样你就可以逐步构建multipleArray，而不是试图在最后一次构建它。此外，如果任何一个字母的查询失败，则只会丢失该字母。仍会添加以下字母。

Answer 3

我将给出一些基本字符的提示，这将为您节省大量代码！你可以对它们进行算术改变字母。

unichar letter = L'A' + i;
tempLike = [NSString stringWithCharacters:&letter length:1];

现在实际的问题是你需要检查每个对象是否为nil并将其替换为自定义对象（通常为[NSNull null]），因为一旦你将nil sentinel传递给方法，它就会认为它是结束。< / p>

Answer 4

我会建议你。实现在进入数据库之前检查字符串的代码。如果string为null，则替换为@“”（空白）。 感谢

Answer 5

在第二个switch语句之前尝试这个：

if (!retval) {
    retval = [NSMutableArray arrayWithObject:[NSNull null]];
} else if (![retval count]) {
    [retval addObject:[NSNull null]];
    NSLog(@"No content");
}
....