1、导入SQLite库和头文件
1 #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。
1 sqlite3 * database; 2 if (sqlite3_open([[self dataFilePath] UTF8String], &database) 3 != SQLITE_OK) { 4 sqlite3_close(database); 5 NSAssert(0, @"Failed to open database"); 6 }
3、确保有一个表来保存数据
1 NSString * createSQL = @"CREATE TABLE IF NOT EXISTS FIELDS " 2 "(ROW INTEGER PRIMARY KEY, FIELD_DATA TEXT);"; 3 char * errorMsg; 4 if (sqlite3_exec (database, [createSQL UTF8String], 5 NULL, NULL, &errorMsg) != SQLITE_OK) { 6 sqlite3_close(database); 7 NSAssert(0, @"Error creating table: %s", errorMsg); 8 }
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。
1 NSString * query = @"SELECT ROW, FIELD_DATA FROM FIELDS ORDER BY ROW"; 2 sqlite3_stmt * statement; 3 if (sqlite3_prepare_v2(database, [query UTF8String], 4 -1, &statement, nil) == SQLITE_OK) 5 { 6 while (sqlite3_step(statement) == SQLITE_ROW) { 7 int row = sqlite3_column_int(statement, 0); 8 char *rowData = (char *)sqlite3_column_text(statement, 1); 9 10 NSString *fieldValue = [[NSString alloc] 11 initWithUTF8String:rowData]; 12 UITextField *field = self.lineFields[row]; 13 field.text = fieldValue; 14 } 15 sqlite3_finalize(statement); 16 } 17 sqlite3_close(database);
5、applicationWillResignActive：方法首先会打开数据库，然后保存数据。
1 UIApplication * app = [UIApplication sharedApplication]; 2 [[NSNotificationCenter defaultCenter] 3 addObserver:self 4 selector:@selector(applicationWillResignActive:) 5 name:UIApplicationWillResignActiveNotification 6 object:app];
1 - (void)applicationWillResignActive:(NSNotification *)notification 2 { 3 sqlite3 * database; 4 if (sqlite3_open([[self dataFilePath] UTF8String], &database) 5 != SQLITE_OK) { 6 sqlite3_close(database); 7 NSAssert(0, @"Failed to open database"); 8 } 9 for (int i = 0; i < 4; i++) { 10 UITextField *field = self.lineFields[i]; 11 // Once again, inline string concatenation to the rescue: 12 char *update = "INSERT OR REPLACE INTO FIELDS (ROW, FIELD_DATA) " 13 "VALUES (?, ?);"; 14 char * errorMsg = NULL; 15 sqlite3_stmt * stmt; 16 if (sqlite3_prepare_v2(database, update, -1, &stmt, nil) 17 == SQLITE_OK) { 18 sqlite3_bind_int(stmt, 1, i); 19 sqlite3_bind_text(stmt, 2, [field.text UTF8String], -1, NULL); 20 } 21 if (sqlite3_step(stmt) != SQLITE_DONE) 22 NSAssert(0, @"Error updating table: %s", errorMsg); 23 sqlite3_finalize(stmt); 24 } 25 sqlite3_close(database); 26 }