iphone开发常用代码

 

//判读对象是否响应某个消息

if( [Square instancesRespondToSelector: @selector(setSize:)] == YES ) {}

 

//根据给定的url获取字符串

 

NSString *jsonString = [NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncodingerror:&error];

 

 

 

我们在定义一个对象的时候，如果暂时不能给对象赋值，或者将对象的地址作为参数传递到别的方法里面，需要将此对象赋值为nil，这样可以避免"EXC_BAD_ACCESS"错误.

 

 

替换字符串
- (NSString *)stringByReplacingOccurrencesOfString:(NSString *)target withString:(NSString *)replacement;


分割字符串
- (NSArray *)componentsSeparatedByString:(NSString *)separator;

//创建sqlite数据库，执行查询

 

 

 

NSString *dbName="/db.sqlite";

NSError *error;

NSFileManager *fileManager = [NSFileManagerdefaultManager];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

NSString *documentsDirectory = [paths objectAtIndex:0];

 NSString *writableDBPath = [documentsDirectory stringByAppendingString:dbName];

    // -- test to see if it exists

BOOL success = [fileManager fileExistsAtPath:writableDBPath];

    

// -- it not yet create,do it.

if(!success){   

    

    NSString *defaultDBPath = [[[NSBundlemainBundle] resourcePath] stringByAppendingString:dbName];

    success = [fileManager copyItemAtPath:defaultDBPath toPath:writableDBPath error:&error];

    if(!success)

    {

        Assert(0, "Failed to create writable database file with message '%s'.", [error localizedDescription]);

    }

}

 

 //打开数据库

 

 

typedefunsigned int    uint32;

    

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    NSString *documentDirectory = [paths objectAtIndex:0];

    NSString *path = [documentDirectory stringByAppendingString:dbName];

    sqlite3                     *database;

    if(sqlite3_open([path UTF8String], &database) == SQLITE_OK)

    {

        // Get the primary key

        sqlite3_stmt *statement;

        constchar *sql = "SELECT id,name,slogan,skips FROM skips WHERE pk=? and desc=?";

        if(sqlite3_prepare_v2(database, sql, -1, &statement, NULL) == SQLITE_OK)

        {

            //绑定查询参数

            sqlite3_bind_int(init_statement, 1, key);

            sqlite3_bind_text(insert_statement, 2, [sInfo.slogan UTF8String], -1, SQLITE_TRANSIENT);

            // -- 循环,执行其他sql也使用这个语句

            while(sqlite3_step(statement) == SQLITE_ROW){

                //取出int型变量

                uint32 stationID = sqlite3_column_int(statement, 0);

                //取出字符串

                NSString name = [NSString stringWithUTF8String:(char*)sqlite3_column_text(statement, 1)];

            }

        }

        //重置查询语句，可以重新绑定参数

        sqlite3_reset(statement);

        //清除数据

        sqlite3_finalize(statement);

        //关闭数据库

        sqlite3_close(database);

    }

 

// 插入数据

// -- get the db

    sqlite3 *database = [StationPlayerAppDelegateInstance].database;

    

    if(insert_statement == nil)

    {

        staticchar *sql = "INSERT INTO favorites (id, name, slogan,orderNumber) VALUES (?, ?, ?,?)";

        if(sqlite3_prepare_v2(database, sql, -1, &insert_statement, NULL) != SQLITE_OK)

        {

            Assert(0, "Failed to prepare insert statement for '%s'.", sqlite3_errmsg(database));

        }

    }

    

    // -- prepare the values

sqlite3_bind_int(insert_statement, 4, sInfo.orderNumber);

    sqlite3_bind_text(insert_statement, 3, [sInfo.sloganUTF8String], -1, SQLITE_TRANSIENT);

    sqlite3_bind_text(insert_statement, 2, [sInfo.nameUTF8String], -1, SQLITE_TRANSIENT);

    sqlite3_bind_int(insert_statement, 1, sInfo.stationID);

    int32 success = sqlite3_step(insert_statement);

    

    sqlite3_reset(insert_statement);

    if(success != SQLITE_ERROR)

    {

        // 取回插入数据的主键

        sInfo.favoritesPrimaryKey = sqlite3_last_insert_rowid(database);

    }

    else

    {

        Assert(0, "Failed to insert into database with message '%s'.", sqlite3_errmsg(database));

    }    

 

 

 // 隐藏navigation bar上的返回按钮，设置为自定义的按钮

 

[self.navigationItemsetHidesBackButton:YES];

UIBarButtonItem *left=[[UIBarButtonItemalloc]initWithTitle:NSLocalizedString(@"Back",@"") style:UIBarButtonItemStyleBorderedtarget:selfaction:@selector(backroot)];

self.navigationItem.leftBarButtonItem=left;