如何在Objective-C中动态分类NSMutableArray？

Question

我正在从sqlite表中检索行，然后动态创建对象，然后将对象添加到nsmutablearray。我的问题是，我无法找到一种方法，可以根据距离属性（是双重）动态分类数组中的对象最大。

我的相关代码看起来像这样：

sqlite3 *database;

//Init the restaurant array
restaurants = [[NSMutableArray alloc] init];

CLLocation *firstLocation = [[[CLLocation alloc] initWithLatitude:userLatitude longitude:userLongitude] autorelease];

//Open the database from the users filesystem
if (sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) {

    //setup the SQL statement and compile it for faster access
    const char *sqlStatement = "select * from restaurant";
    sqlite3_stmt *compiledStatement;

    if (sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) {

        //loop through the results and add them to the feeds array
        while (sqlite3_step(compiledStatement) == SQLITE_ROW) {

            //read the data from the result row
            NSString *aName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 1)];
            NSString *aAddress = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 2)];
            NSString *aCity = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 3)];
            NSString *aProvinceState = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 4)];
            NSString *aPostalZipCode = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 5)];
            NSString *aCountry = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 6)];
            NSString *aPhoneNumber = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 7)];
            NSString *aHours = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 8)];
            double aLat = sqlite3_column_double(compiledStatement, 9);
            double aLon = sqlite3_column_double(compiledStatement, 10);

            CLLocation *secondLocation = [[[CLLocation alloc] initWithLatitude:aLat longitude:aLon] autorelease];
            CLLocationDistance restDistance = [secondLocation distanceFromLocation:firstLocation];

            CLLocationDistance distanceKm = restDistance / 1000.0;

            NSString *aDist = [[NSString alloc] initWithFormat: @"%f", distanceKm];

            Restaurant *restaurant = [[Restaurant alloc] initWithName:aName address:aAddress city:aCity provinceState:aProvinceState postalZipCode:aPostalZipCode country:aCountry phoneNumber:aPhoneNumber hours:aHours latitude:aLat longitude:aLon distance:aDist];

            //add the restaurant object to the restaurant array
            [restaurants addObject:restaurant];

            [restaurant release];

        }


    }

    sqlite3_finalize(compiledStatement);

}

sqlite3_close(database);

}

此功能完成课程后，餐厅阵列应该是一个排序的阵列，其中包含按最接近（最小距离双值）到最远（最大距离双值）的餐厅对象。

Answer 1

使用Nsmutablearray的sortusingSelector来调用您的餐厅对象的比较功能。

@implementation Restaurant

- (double) distance { return _distance; }

- (NSComparisonResult) compareDistance:(Restaurant *) iRHS {
    double                      lhs, rhs;

    lhs = [self distance];
    rhs = [iRHS distance];

    if ( lhs < rhs ) return NSOrderedAscending;
    if ( lhs > rhs ) return NSOrderedDescending;

    return NSOrderedSame;
}


@end

...

[restaurants sortUsingSelector: @selector(compareDistance:)];