数据库SQLite应用

1、导入SQLite库和头文件

#import <sqlite3.h>

2、打开数据库，如果在打开的时候遇到了问题，则关闭它并抛出一个断言错误。

     sqlite3 * database;
     if (sqlite3_open([[self dataFilePath] UTF8String], &database)
         != SQLITE_OK) {
         sqlite3_close(database);
         NSAssert(, @"Failed to open database");
     }

3、确保有一个表来保存数据

     NSString * createSQL = @"CREATE TABLE IF NOT EXISTS FIELDS "
     "(ROW INTEGER PRIMARY KEY, FIELD_DATA TEXT);";
     char * errorMsg;
     if (sqlite3_exec (database, [createSQL UTF8String],
                       NULL, NULL, &errorMsg) != SQLITE_OK) {
         sqlite3_close(database);
         NSAssert(, @"Error creating table: %s", errorMsg);
     }

4、加载数据

创建一个SELECT来从数据库请求所有行，并要求SQLite准备我们的SELECT。这里是告诉SQLite按行号排序各行，以便我们总是以相同顺序获取他们。否则SQLite会按内部存储顺序返回各行。

     NSString * query = @"SELECT ROW, FIELD_DATA FROM FIELDS ORDER BY ROW";
     sqlite3_stmt * statement;
     if (sqlite3_prepare_v2(database, [query UTF8String],
                            -, &statement, nil) == SQLITE_OK)
     {
         while (sqlite3_step(statement) == SQLITE_ROW) {
             int row = sqlite3_column_int(statement, );
             char *rowData = (char *)sqlite3_column_text(statement, );

             NSString *fieldValue = [[NSString alloc]
                                     initWithUTF8String:rowData];
             UITextField *field = self.lineFields[row];
             field.text = fieldValue;
         }
         sqlite3_finalize(statement);
     }
     sqlite3_close(database);

5、applicationWillResignActive：方法首先会打开数据库，然后保存数据。

     UIApplication * app = [UIApplication sharedApplication];
     [[NSNotificationCenter defaultCenter]
      addObserver:self
      selector:@selector(applicationWillResignActive:)
      name:UIApplicationWillResignActiveNotification
      object:app];

 - (void)applicationWillResignActive:(NSNotification *)notification
 {
     sqlite3 * database;
     if (sqlite3_open([[self dataFilePath] UTF8String], &database)
         != SQLITE_OK) {
         sqlite3_close(database);
         NSAssert(, @"Failed to open database");
     }
     for (int i = ; i < ; i++) {
         UITextField *field = self.lineFields[i];
         // Once again, inline string concatenation to the rescue:
         char *update = "INSERT OR REPLACE INTO FIELDS (ROW, FIELD_DATA) "
         "VALUES (?, ?);";
         char * errorMsg = NULL;
         sqlite3_stmt * stmt;
         if (sqlite3_prepare_v2(database, update, -, &stmt, nil)
             == SQLITE_OK) {
             sqlite3_bind_int(stmt, , i);
             sqlite3_bind_text(stmt, , [field.text UTF8String], -, NULL);
         }
         if (sqlite3_step(stmt) != SQLITE_DONE)
             NSAssert(, @"Error updating table: %s", errorMsg);
         sqlite3_finalize(stmt);
     }
     sqlite3_close(database);
 }