iOS 新浪微部落格戶端Demo實踐之(二) 授權頁面

前面一篇博文--- 新浪微部落格戶端Demo實踐之（一）OAuth2.0認證 已經談得如何擷取access_token了，那麼現在要做的是授權介面的視圖部分--UI。

    授權頁面是一個webview，根據url就可以load到授權介面，下面就是授權的API 是https://api.weibo.com/oauth2/authorize，完整的授權介面的url如下

+ (NSString *) returnOAuthUrlString {    return [NSString stringWithFormat:@"%@?client_id=%@&redirect_uri=%@&response_type=code&display=mobile&state=authorize",OAuth_URL,APP_KEY,APP_REDIRECT_URL];}

下面介紹一下我在這個視圖中是如何處理的。

（1）首先要儲存acess_token，用NSUserDefaults實現資料持久化，這樣的好處是，如果是第一次登陸就出現授權介面，授權後儲存access_token，之後登陸就不出現授權介面，直接進入微博首頁視圖了。

處理的相關代碼如下（在這個處理過程中我還添加了一個方法：擷取使用者的uid，這個參數在之後的API 呼叫中也是經常用到的，uid也儲存到NSUserDefaults）：

- (void) getAccessToken : (NSString *) code{        //access token調用URL的string    NSMutableString *accessTokenUrlString = [[NSMutableString alloc] initWithFormat:@"%@?client_id=%@&client_secret=%@&grant_type=authorization_code&redirect_uri=%@&code=",ACCESS_TOKEN_URL,APP_KEY,APP_SECRET,APP_REDIRECT_URL];    [accessTokenUrlString appendString:code];        //同步POST請求    NSURL *urlstring = [NSURL URLWithString:accessTokenUrlString];    //第二步，建立請求    NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:urlstring cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];    [request setHTTPMethod:@"POST"];//佈建要求方式為POST，預設為GET        //第三步，串連伺服器    NSData *received = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];    NSString *backString = [[NSString alloc]initWithData:received encoding:NSUTF8StringEncoding];        //如何從backString中擷取到access_token    NSDictionary *dictionary = [backString objectFromJSONString];      [[NSUserDefaults standardUserDefaults] setObject:[dictionary objectForKey:@"access_token"] forKey:@"access_token"];    [[NSUserDefaults standardUserDefaults] synchronize];    //在擷取到access_token之後就擷取使用者uid    [self getUIDString];}- (void) getUIDString {        NSString *uidURLString = [[NSString alloc] initWithFormat:@"%@?access_token=%@",GET_UID_URL,[InfoForSina returnAccessTokenString]];    NSURLRequest *request = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:uidURLString]];    NSError *error;    NSData *uidData = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:&error];    NSString *uidString = [[NSString alloc] initWithData:uidData encoding:NSUTF8StringEncoding];        NSDictionary *uidDictionary = [uidString objectFromJSONString];            [[NSUserDefaults standardUserDefaults] setObject:[uidDictionary objectForKey:@"uid"] forKey:@"uid"];    [[NSUserDefaults standardUserDefaults] synchronize];}

下面簡單介紹一下NSUserDefaults：

The NSUserDefaults class provides convenience methods for accessing common types such as floats, doubles, integers, Booleans, and URLs. A default object must be a property list, that is, an instance of (or for collections
a combination of instances of): NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary. If you want to store any other type of object, you should typically archive it to create an instance of NSData. 
NSUserDefaults 是本機存放區資料最簡單的一種方式，NSUserDefaults用於儲存資料量小的資料，例如使用者配置。並不是所有的東西都能往裡放的，只支援：NSString, NSNumber, NSDate, NSArray, NSDictionary，如果你想儲存一些自訂的（除了前面提到的以外）資料，你就應該將他轉換成NSData
的形式（有人可能會想到說把我自訂的資料存到NSArray中，不就可以了嗎？答案是否定的！）

  The synchronize method, which is automatically invoked at periodic intervals, keeps the in-memory cache in sync with a user’s defaults database.

定期調用同步方法 synchronize就可以保持資料，實現資料同步

Values returned from NSUserDefaults are immutable, even if you set a mutable object as the value.

從NSUserDefaults進行返回的值是不可改變的，即使你設定一個可變的對象作為value。

Persistence of NSURL and file reference URLs

當然也可以持久化保持NSURL和URLs

可以在文檔中找到相關的getter和setter 方法進行設定。這裡就不多說了。

下面詳細講一下如何在NSUserDefaults讀取和寫入自訂的資料（一般都是些自訂的類）。

解決方案：對自訂的類對象進行編碼成NSData形式進行儲存，使用時再對其進行解碼。需要在自訂的類中實現<NSCoding>協議中的兩個方法：- (id) initWithCoder: (NSCoder *)coder （編碼）  和  - (void) encodeWithCoder:(NSCoder
*)aCoder （解碼）。

下面以一個小小的demo程式實踐一下。我定義了一個student類，裡面有兩個property：chinaeseNameString  和  englishNameString，在實現方法中實現編碼和解碼的兩個方法。（注意添加NSCoding協議）。

  以下分別是.h和.m檔案代碼，十分的簡單。

#import <Foundation/Foundation.h>@interface Student : NSObject <NSCoding>@property (nonatomic, strong) NSString *chinaeseNameString;@property (nonatomic, strong) NSString *englishNameString;@end

#import "Student.h"@implementation Student@synthesize chinaeseNameString = _chinaeseNameString;@synthesize englishNameString = _englishNameString;- (void) encodeWithCoder:(NSCoder *)aCoder {    [aCoder encodeObject:_chinaeseNameString forKey:@"chinaeseNameString"];    [aCoder encodeObject:_englishNameString forKey:@"englishNameString"];}- (id) initWithCoder: (NSCoder *)coder {    if (self = [super init])    {        _chinaeseNameString = [coder decodeObjectForKey:@"chinaeseNameString"];        _englishNameString = [coder decodeObjectForKey:@"englishNameString"];    }    return self;}@end

下面這段代碼建立一個student執行個體，編碼成NSData，儲存到NSUserDefaults，然後取出解碼，進行顯示。

Student *stu = [[Student alloc] init];    stu.chinaeseNameString= @"小鄧";    stu.englishNameString = @"xiaodeng";        NSData *data = [[NSData alloc] init];    data = [NSKeyedArchiver archivedDataWithRootObject:stu];        [[NSUserDefaults standardUserDefaults] setObject:data forKey:@"Student"];    [[NSUserDefaults standardUserDefaults] synchronize];        Student *anotherStu = [[Student alloc] init];    NSData *anotherData = [[NSData alloc] init];    anotherData = [[NSUserDefaults standardUserDefaults] objectForKey:@"Student"];    anotherStu = [NSKeyedUnarchiver unarchiveObjectWithData:anotherData];        NSLog(@"anotherStu chinaeseName:%@",anotherStu.chinaeseNameString);    NSLog(@"anotherStu englishName:%@",anotherStu.englishNameString);

注意到兩個方法：

+ (id)unarchiveObjectWithData:(NSData *)data
Decodes and returns the object graph previously encoded by NSKeyedArchiver and stored in a given NSData object.是 NSKeyedArchiver 的類方法

+ (id)unarchiveObjectWithData:(NSData *)data
Decodes and returns the object graph previously encoded by NSKeyedArchiver and stored in a given NSData object.  是 NSKeyedUnarchiver 的類方法

（2）程式啟動並執行最開始我設定了一個歡迎介面視圖imageview，顯示一張sina微博的圖片，延遲0.8秒進行動畫跳轉。根據NSUserDefaults中是否儲存有access_token決定跳轉到哪一個視圖（授權視圖webView，還是微博首頁視圖mainView）。

代碼實現如下：

- (void)viewDidLoad{    [super viewDidLoad];// Do any additional setup after loading the view.    hud = [[MBProgressHUD alloc] init];    if ([[NSUserDefaults standardUserDefaults] objectForKey:@"access_token"] == nil) {        hud.labelText = @"正在載入授權頁面...";        [hud show:YES];        [self.view addSubview:hud];                NSString *oauthUrlString = [InfoForSina returnOAuthUrlString];        NSURLRequest *request = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:oauthUrlString]];        [self.webView setDelegate:self];        [self.webView loadRequest:request];        _imageView.hidden = NO;        timer = [NSTimer scheduledTimerWithTimeInterval:0.8 target:self selector:@selector(goWebView) userInfo:nil repeats:NO];    }    else {        hud.labelText = @"正在載入微博內容...";        [hud show:YES];        [self.view addSubview:hud];        _imageView.hidden = NO;        timer = [NSTimer scheduledTimerWithTimeInterval:0.8 target:self selector:@selector(goMainView) userInfo:nil repeats:NO];    }    }- (void) goWebView {        [UIView beginAnimations:nil context:NULL];[UIView setAnimationDuration:0.8];[UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight                           forView:self.view cache:YES];    _imageView.hidden = YES;    [UIView commitAnimations];}- (void) goMainView {    [UIView beginAnimations:nil context:NULL];[UIView setAnimationDuration:0.8];[UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight                           forView:self.view cache:YES];    _imageView.hidden = YES;    [UIView commitAnimations];    [hud removeFromSuperview];    [self performSegueWithIdentifier:@"MainSegue" sender:nil];}- (void) webViewDidFinishLoad:(UIWebView *)webView {    [hud removeFromSuperview];}