我正在从SQLite表中检索行,然后动态创建一个对象,然后将该对象添加到NSMutableArray。我的问题是我无法找到一种方法来根据distance属性(这是一个double)动态地对数组中的对象进行排序,因为我将每个对象添加到for循环中的NSMutableArray,从最小到最大。
我的相关代码如下所示:
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);
}
一旦此功能完成其过程,餐馆阵列应该是一个排序的数组,其中包含餐馆对象,这些对象按最近(最小距离双倍值)到最远(最大距离双倍值)的顺序排列。
使用NSMutableArray的sortUsingSelector来调用Restaurant对象上的比较函数。
@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:)];