以编程方式将 SQLite 数据导出到 iOS 中的 Excel

Question

在我的应用程序中，我使用 sqlite 作为后端（在本地存储数据）。 我能够将数据插入到我的表中。但我想要做的是，想以编程方式将我所有的 sqlite 数据导入到 excel 中。我不想为这个应用程序使用服务器。一旦生成了 excel 表，用户应该能够邮寄那张纸。 这在 iPhone 中是否可行： 请帮帮我。

以下是我将数据插入表格的代码：

-(IBAction)Login
{
sqlite3_stmt *stmt;
        char *errorMsg; 
        char *update1 = "insert into Login1 values (?,?,?,?);";
        int x = sqlite3_prepare_v2(database, update1, -1, &stmt, nil);

    if (x == SQLITE_OK) 
    { 
        sqlite3_bind_text(stmt, 1, NULL,-1, NULL);
        sqlite3_bind_text(stmt, 2, [USERID UTF8String],-1, NULL);
        sqlite3_bind_text(stmt, 3, [str1 UTF8String],-1, NULL);
        sqlite3_bind_text(stmt, 4, [str4 UTF8String],-1, NULL);


    } 

    if (sqlite3_step(stmt) != SQLITE_DONE)
        NSLog(@"Error: %@",errorMsg); 
    sqlite3_finalize(stmt);

}

Answer 1

对于我这样做的应用程序，SQLite 数据相当大。因此，我使用后台线程将所有数据导出到 Excel 可以导入的 CSV（逗号分隔值）文件，然后以 CSV 文件作为附件打开邮件编写器。如果您的数据很小，您可能不需要使用后台线程：

- (IBAction) export: (id) sender
{    
    // in my full code, I start a UIActivityIndicator spinning and show a 
    //  message that the app is "Exporting ..."

    [self performSelectorInBackground: @selector(exportImpl) withObject: nil];
}

这里是exportImpl

- (void) exportImpl
{
    NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];

    NSArray* documentPaths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSSystemDomainMask, YES);
    NSString* documentsDir = [documentPaths objectAtIndex:0];
    NSString* csvPath = [documentsDir stringByAppendingPathComponent: @"export.csv"];

    // TODO: mutex lock?
    [sqliteDb exportCsv: csvPath];

    [pool release];

    // mail is graphical and must be run on UI thread
    [self performSelectorOnMainThread: @selector(mail:) withObject: csvPath waitUntilDone: NO];
}

- (void) mail: (NSString*) filePath
{
    // here I stop animating the UIActivityIndicator

    // http://howtomakeiphoneapps.com/home/2009/7/14/how-to-make-your-iphone-app-send-email-with-attachments.html
    BOOL success = NO;
    if ([MFMailComposeViewController canSendMail]) {
        // TODO: autorelease pool needed ?
        NSData* database = [NSData dataWithContentsOfFile: filePath];

        if (database != nil) {
            MFMailComposeViewController* picker = [[MFMailComposeViewController alloc] init];
            picker.mailComposeDelegate = self;
            [picker setSubject:[NSString stringWithFormat: @"%@ %@", [[UIDevice currentDevice] model], [filePath lastPathComponent]]];

            NSString* filename = [filePath lastPathComponent];
            [picker addAttachmentData: database mimeType:@"application/octet-stream" fileName: filename];
            NSString* emailBody = @"Attached is the SQLite data from my iOS device.";
            [picker setMessageBody:emailBody isHTML:YES];

            [self presentModalViewController:picker animated:YES];
            success = YES;
            [picker release];
        }
    }

    if (!success) {
        UIAlertView* warning = [[UIAlertView alloc] initWithTitle: @"Error"
                                                          message: @"Unable to send attachment!"
                                                         delegate: self
                                                cancelButtonTitle: @"Ok"
                                                otherButtonTitles: nil];
        [warning show];
        [warning release];
    }
}

然后，我有一个封装我所有 SQLite 数据的类。这个类是唯一一个进行 sqlite 调用的类。在这个类中，我有一种方法可以将数据导出到我的应用程序 caches 目录中的 CSV 文件中。上面代码中的变量sqliteDb就是这个类的一个实例。导出数据的方法如下：

-(void) exportCsv: (NSString*) filename
{
    // We record this filename, because the app deletes it on exit
    self.tempFile = filename;

    NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
    // Setup the database object
    sqlite3* database;

    // Open the database from the users filessytem
    if (sqlite3_open([self.databasePath UTF8String], &database) == SQLITE_OK)
    {
        [self createTempFile: filename];
        NSOutputStream* output = [[NSOutputStream alloc] initToFileAtPath: filename append: YES];
        [output open];
        if (![output hasSpaceAvailable]) {
            NSLog(@"No space available in %@", filename);
            // TODO: UIAlertView?
        } else {
            NSString* header = @"Source,Time,Latitude,Longitude,Accuracy\n";
            NSInteger result = [output write: [header UTF8String] maxLength: [header length]];
            if (result <= 0) {
                NSLog(@"exportCsv encountered error=%d from header write", result);
            }

            BOOL errorLogged = NO;
            NSString* sqlStatement = @"select timestamp,latitude,longitude,horizontalAccuracy from my_sqlite_table";

            // Setup the SQL Statement and compile it for faster access
            sqlite3_stmt* compiledStatement;
            if (sqlite3_prepare_v2(database, [sqlStatement UTF8String], -1, &compiledStatement, NULL) == SQLITE_OK)
            {
                 // Loop through the results and write them to the CSV file
                 while (sqlite3_step(compiledStatement) == SQLITE_ROW) {
                     // Read the data from the result row
                     NSInteger secondsSinceReferenceDate = (NSInteger)sqlite3_column_double(compiledStatement, 0);
                     float lat = (float)sqlite3_column_double(compiledStatement, 1);
                     float lon = (float)sqlite3_column_double(compiledStatement, 2);
                     float accuracy = (float)sqlite3_column_double(compiledStatement, 3);

                     if (lat != 0 && lon != 0) {
                         NSDate* timestamp = [[NSDate alloc] initWithTimeIntervalSinceReferenceDate: secondsSinceReferenceDate];
                         NSString* line = [[NSString alloc] initWithFormat: @"%@,%@,%f,%f,%d\n",
                                       table, [dateFormatter stringFromDate: timestamp], lat, lon, (NSInteger)accuracy];
                         result = [output write: [line UTF8String] maxLength: [line length]];
                         if (!errorLogged && (result <= 0)) {
                             NSLog(@"exportCsv write returned %d", result);
                             errorLogged = YES;
                         }
                         [line release];
                         [timestamp release];
                     }
                     // Release the compiled statement from memory
                     sqlite3_finalize(compiledStatement);
                 }
            }
        }
        [output close];
        [output release];
    }

    sqlite3_close(database);
    [pool release];
}

-(void) createTempFile: (NSString*) filename {
    NSFileManager* fileSystem = [NSFileManager defaultManager];
    [fileSystem removeItemAtPath: filename error: nil];

    NSMutableDictionary* attributes = [[NSMutableDictionary alloc] init];
    NSNumber* permission = [NSNumber numberWithLong: 0640];
    [attributes setObject: permission forKey: NSFilePosixPermissions];
    if (![fileSystem createFileAtPath: filename contents: nil attributes: attributes]) {
        NSLog(@"Unable to create temp file for exporting CSV.");
        // TODO: UIAlertView?
    }
    [attributes release];
}

我的代码正在导出位置信息数据库。显然，在 exportCsv 中，您需要将我的 sqlite 调用替换为适合您的数据库内容的调用。

此外，代码将数据存储在临时文件中。您可能需要决定何时清除这些临时文件。

显然，此代码是在 ARC 可用之前编写的。根据需要进行调整。