从一个视图控制器访问 CLLocationManager 变量到另一个视图控制器

Posted 2023-03-05

【中文标题】从一个视图控制器访问 CLLocationManager 变量到另一个视图控制器

【英文标题】：Accessing CLLocationManager variable from one viewcontroller to another viewcontroller

【发布时间】：2014-12-15 15:28:38

【问题描述】：

在 ios 中，我已经像这样声明了 CLLocationManager 变量：

DashBoardViewController.h

#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>

@class AppDelegate;
@interface DashBoardViewController : UIViewController<CLLocationManagerDelegate, UIAlertViewDelegate>

    AppDelegate *appDel;

@property(nonatomic,strong) CLLocationManager *locationManager;
@property (nonatomic,retain) CLLocation *current;

-(void)localnotification;
@end

在 DashBoardViewController.m 文件中：

#import "DashBoardViewController.h"
#import "AppDelegate.h"

#define IS_OS_8_OR_LATER ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0)

@interface DashBoardViewController ()
@end

@implementation DashBoardViewController

@synthesize current,locationManager;
- (void)viewDidLoad

    [super viewDidLoad];
    appDel = (AppDelegate*)[UIApplication sharedApplication].delegate;
    [self localnotification];


-(void)localnotification 
    locationManager = [[CLLocationManager alloc] init];
    locationManager.delegate = self;
    locationManager.distanceFilter = kCLDistanceFilterNone;
    locationManager.desiredAccuracy = kCLLocationAccuracyBest;

    if(IS_OS_8_OR_LATER) 
        [locationManager requestAlwaysAuthorization];
    

    [locationManager startMonitoringSignificantLocationChanges];

我也实现了

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations

  //some code

现在我正在像这样访问 "locationManager" 和 "localnotification" 方法 SettingsViewController.m

#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>
#import "DashBoardViewController.h"

//To stop the Location Manager service
- (IBAction)stopButtonAction:(id)sender 
DashBoardViewController *dash=[[DashBoardViewController alloc] init];
    dash.locationManager=nil;


//To start the Location Manager service
- (IBAction)startButtonAction:(id)sender 

    DashBoardViewController *dash=[[DashBoardViewController alloc] init];
    [dash localnotification];

但它不起作用。所有时间 locationManager 返回 null。这段代码有什么问题？

【参考方案1】：

当你

DashBoardViewController *dash=[[DashBoardViewController alloc] init];

它创建一个新的DashBoardViewController 实例。您可以在 AppDelegate 中定义 locationManager 并从代码中的任何位置直接访问它。

AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
appDelegate.locationManager = nil;

【参考方案2】：

在你分配初始化视图控制器时不会调用viewDidLoad。它在加载视图时调用，稍后在您实际显示它时完成。这就是为什么它为零。如果您想跨多个视图控制器访问它，我建议在 AppDelegate 中创建位置管理器。