如何知道用户是否更新了应用程序或安装了新副本？

Question

I will be sending out an update to my app with a new data structure, therefore if a user is updating my app I need to update their current data. So I was wondering how can I programatically tell if the user updated my app or installed a new copy (if a new copy is installed I don't need to update anything) ?

Answer 1

That depends on the kind of data structure you're using.

In general, I would advise you against relying on checking your application version: a user using 2.0 might have just upgraded or it might be a new user.

I'd rather check if there's a data structure already, and act accordingly. Assuming that you're using a Sqlite-backed Core Data storage, you can either check whether the .sqlite file exists, or check if there are objects in your storage.

Answer 2

Checking the data structure is a solid solution. I began to worry in my own apps about folks who don't upgrade for several versions. I felt this would lead to a myriad of structure checks. The code I show below determines and stores the version and previous version in the NSUserDefaults . You could code for those varying version difference scenarios if needed.

NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
BOOL versionUpgraded;
NSString *version = [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleVersion"];
NSString *preVersion = [prefs stringForKey:@"appVersion"];

if ([prefs stringForKey:@"appVersion"] != nil) {
    //see if version is the same as prior
    //if not it is an Upgraded
    versionUpgraded = !([preVersion isEqualToString: version]);
} else {
    //nil means new install
            //This needs to be YES for the case that
            //"appVersion" is not set anywhere else.
    versionUpgraded = YES; 
}

if (versionUpgraded) {
    [prefs setObject:version forKey:@"appVersion"];
    [prefs setObject:preVersion forKey:@"prevAppVersion"];

    [prefs synchronize];
}

Answer 3

Just save the bundle version somewhere and check if it differs from

[[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleVersion"]]

on each app startup.

Answer 4

I have created a category for this. Just implement the two new delegate calls found in the header. It relies quite heavily on the obj-c runtime libraries, so make sure you are confident with them before using this.

.h

#import <UIKit/UIKit.h>

@protocol UIApplicationDelegate <UIApplicationDelegate>
@optional
- (void) application:(UIApplication *)application willUpdateToVersion: (NSString*) newVersion fromVersion: (NSString*) previousVersion;
- (void) application:(UIApplication *)application didUpdateToVersion: (NSString*) newVersion fromVersion: (NSString*) previousVersion;

@end

@interface UIApplication (Versioning)

@end

.m

#import "UIApplication+Versioning.h"

#import <objc/message.h>
#import <objc/runtime.h>

static NSString* UIApplicationVersionFileName = @"app.ver";

@implementation UIApplication (Versioning)

+ (void) load {
    Method original, swizzled;

    original = class_getInstanceMethod(self, @selector(setDelegate:));
    swizzled = class_getInstanceMethod(self, @selector(swizzled_setDelegate:));

    method_exchangeImplementations(original, swizzled);
}

- (void) swizzled_setDelegate: (id<UIApplicationDelegate>) delegate {

    IMP implementation = class_getMethodImplementation([self class], @selector(swizzled_application:didFinishLaunchingWithOptions:));
    class_addMethod([delegate class], @selector(swizzled_application:didFinishLaunchingWithOptions:), implementation, "B@:@@");

    Method original, swizzled;

    original = class_getInstanceMethod([delegate class], @selector(application:didFinishLaunchingWithOptions:));
    swizzled = class_getInstanceMethod([delegate class], @selector(swizzled_application:didFinishLaunchingWithOptions:));

    method_exchangeImplementations(original, swizzled);

    [self swizzled_setDelegate: delegate];
}

- (BOOL)swizzled_application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    //Check for a version change
    NSError* error;
    NSArray* directories = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString* versionFilePath = [[directories objectAtIndex: 0] stringByAppendingPathComponent: UIApplicationVersionFileName];
    NSString* oldVersion = [NSString stringWithContentsOfFile: versionFilePath
                                                     encoding: NSUTF8StringEncoding
                                                        error: &error];
    NSString* currentVersion = [[[NSBundle mainBundle] infoDictionary] objectForKey: @"CFBundleVersion"];

    switch (error.code) {
        case NSFileReadNoSuchFileError:
        {
            //Delegate methods will not be called first time
            oldVersion = [currentVersion copy];
            [currentVersion writeToFile: versionFilePath
                             atomically: YES
                               encoding: NSUTF8StringEncoding
                                  error: &error];
            break;
        }
        default:
        {
            NSLog(@"Warning: An error occured will loading the application version file -> Recreating file");
            [[NSFileManager defaultManager] removeItemAtPath: versionFilePath
                                                       error: nil];
            oldVersion = [currentVersion copy];
            [currentVersion writeToFile: versionFilePath
                             atomically: YES
                               encoding: NSUTF8StringEncoding
                                  error: &error];
            break;
        }
    }

    if( ![oldVersion isEqualToString: currentVersion] ) {

        if ([[application delegate] respondsToSelector: @selector(application:willUpdateToVersion:fromVersion:)]) {
            objc_msgSend([application delegate], @selector(application:willUpdateToVersion:fromVersion:), currentVersion, oldVersion);
        }

        [currentVersion writeToFile: versionFilePath
                         atomically: YES
                           encoding: NSUTF8StringEncoding
                              error: &error];

        if ([[application delegate] respondsToSelector: @selector(application:didUpdateToVersion:fromVersion:)]) {
            objc_msgSend([application delegate], @selector(application:willUpdateToVersion:fromVersion:), currentVersion, oldVersion);
        }

    }

    SEL realSelector =  @selector(swizzled_application:didFinishLaunchingWithOptions:);
    return (BOOL) objc_msgSend([application delegate], realSelector, application, launchOptions);
}

@end