按与当前位置的距离对 TableView 进行排序

Question

我有一个包含经纬度信息的 SQL 数据库。我找到了我当前的位置，并且能够获得每个位置与我当前位置的距离。我可以让我的 tableview 显示这个距离，但我知道我想对该 tableview 进行排序，以便首先列出最接近的。

我的想法是我需要将距离添加到我的 SQL DB 数据中，以某种方式对其进行排序，然后将该信息显示回 tableview。

我的想法是我会在我的 TableView 中完成所有这些工作。寻找有关如何执行此操作以及是否应该在 tableview 中执行此操作的指导。

#import "TulsaMasterViewController.h"
#import "TulsaDetailViewController.h"
#import "Bars.h"
#import "BarDatabase.h"

@implementation TulsaMasterViewController

@synthesize barArray = _barArray;
@synthesize currentLat = _currentLat;


- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
currentLat = newLocation;

if (newLocation.horizontalAccuracy <= 100.0f) {
    [lm stopUpdatingLocation];
}

[self.tableView reloadData];
}

- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
{
NSString *msg = [[NSString alloc]initWithString:@"Error obtaining location"];
UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Error" message:msg delegate:nil cancelButtonTitle:@"Done" otherButtonTitles:nil];
[alert show];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return [self.barArray count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

static NSString *CellIdentifier = @"Cell";

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
    cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
}

//Get the object from the array.
Bars *barObj = [self.barInfo objectAtIndex:indexPath.row];

//Set the name.
cell.textLabel.text = barObj.barName;

if (currentLat == nil) {
    cell.detailTextLabel.text = [NSString stringWithFormat:@"?"];
}else
{
    cell.detailTextLabel.text = [NSString stringWithFormat:@"%.02f", cachedDist];
}

// Set up the cell
return cell;
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([[segue identifier] isEqualToString:@"ShowDetails"]) {
    TulsaDetailViewController *detailViewController = [segue destinationViewController];

    detailViewController.detailItem = [self.barArray objectAtIndex:[self.tableView indexPathForSelectedRow].row];
}
}

- (void)viewDidLoad
{
[super viewDidLoad];

self.barArray = [BarDatabase database].barInfo;

lm = [[CLLocationManager alloc] init];
lm.delegate = self;
[lm startUpdatingLocation];
}

- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];

for (Bars *barObj in barArray) {
    NSString *strLat = barObj.Lat;
    NSString *strLong = barObj.Long;
    CLLocation *barLocation = [[CLLocation alloc] initWithLatitude:[strLat doubleValue] longitude:[strLong doubleValue]];
    CLLocationDistance distance = [currentLat distanceFromLocation:barLocation]/1000;

    [barArray addObject:[NSNumber numberWithDouble:distance]];
    NSSortDescriptor *sort=[NSSortDescriptor sortDescriptorWithKey:@"cachedDist" ascending:YES];
    [barArray sortUsingDescriptors:[NSArray arrayWithObject:sort]];
}

我的其余代码供参考

酒吧.h

#import <Foundation/Foundation.h>

@interface Bars : NSObject {
    NSString *barName;
    NSString *barAddress;
    NSString *Lat;
    NSString *Long;
    NSString *cachedDist;
}

@property (nonatomic, copy) NSString *barName;
@property (nonatomic, copy) NSString *barAddress;
@property (nonatomic, copy) NSString *Lat;
@property (nonatomic, copy) NSString *Long;
@property (nonatomic, copy) NSString *cachedDist;

- (id)initWithName:(NSString *)name address:(NSString *)address latitude:(NSString *)latitude longitude:(NSString *)longitude distance:(NSString *)distance;

@end

酒吧.m

#import "Bars.h"

@implementation Bars

@synthesize barName = _barName;
@synthesize barAddress = _barAddress;
@synthesize Lat = _Lat;
@synthesize Long = _Long;
@synthesize cachedDist = _cachedDist;

- (id)initWithName:(NSString *)name address:(NSString *)address latitude:(NSString *)latitude longitude:(NSString *)longitude distance:(NSString *)distance;
{
if ((self = [super init])) {
    self.barName = name;
    self.barAddress = address;
    self.Lat = latitude;
    self.Long = longitude;
    self.cachedDist = distance;
}
return self;
}

@end

BarDatabase.h

#import <Foundation/Foundation.h>
#import <sqlite3.h>

@interface BarDatabase : NSObject
{
    sqlite3 *_database;
}

+ (BarDatabase *)database;
- (NSMutableArray *)barInfo;

@end

BarDatabase.m

#import "BarDatabase.h"
#import "Bars.h"

@implementation BarDatabase

static BarDatabase *_database;

+ (BarDatabase *)database {
if (_database == nil) {
    _database = [[BarDatabase alloc] init];
}
return _database;
}

- (id)init {
if ((self = [super init])) {
    NSString *sqLiteDb = [[NSBundle mainBundle] pathForResource:@"TulsaBars" 
                                                         ofType:@"sqlite"];

    if (sqlite3_open([sqLiteDb UTF8String], &_database) != SQLITE_OK) {
        NSLog(@"Failed to open database!");
    }
}
return self;
}

- (void)dealloc {
sqlite3_close(_database);
}

- (NSMutableArray *)barInfo {

NSMutableArray *retval = [[NSMutableArray alloc] init];
NSString *query = @"SELECT * FROM TulsaBars";
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, 1);
        char *addressChars = (char *) sqlite3_column_text(statement, 2);
        char *latChars = (char *) sqlite3_column_text(statement, 8);
        char *longChars = (char *) sqlite3_column_text(statement, 9);
        NSString *name = [[NSString alloc] initWithUTF8String:nameChars];
        NSString *address = [[NSString alloc] initWithUTF8String:addressChars];
        NSString *latitude = [[NSString alloc] initWithUTF8String:latChars];
        NSString *longitude = [[NSString alloc] initWithUTF8String:longChars];

        Bars *info = [[Bars alloc]
                      initWithName:name address:address latitude:latitude longitude:longitude];                        
        [retval addObject:info];
    }
    sqlite3_finalize(statement);
}
return retval;

}
@end

Answer 1

嗯。在 cellForRowAtIndexPath 内不应该发生排序。在游戏中为时已晚。如果每个单元格为 1 个条形，并且条形应按距离排序，我建议在您的 self.barInfo 的惰性 getter 中实现排序（如果这是您的条形列表）。

我不确定您的模型是什么样的，但如果每个条形对象都有一个与您的参考点的距离属性，那么您的排序看起来与您在那里的相似。

这种排序只会在第一个单元格被加载（即“惰性”部分）然后被缓存时发生。所以你的 cellForRowAtIndexPath: 只会在它的 indexPath 行中请求模型对象，相信它的顺序是正确的。

我不确定您对这个术语了解多少，所以请随时提出澄清问题，我会重复回答。

分享更多代码后编辑： 我认为您应该向名为 cachedDistance 之类的栏添加一个@property，并且每当您进入屏幕（viewWillAppear）时，迭代这些栏并设置它们的缓存距离（使用与 cellForRow 中类似的代码...）。然后为 self.barArray 实现一个 getter：-(NSArray *)barArray，它本质上返回使用 sortDescriptor 排序的 barArray，其中缓存的距离属性的名称作为它的键。这将大大简化您的 cellForRow... 代码。

然后，您可以扩展逻辑以在获取位置更新时重新计算距离，也许只有当它与之前的距离有一定距离时。