UIAlertController的使用方法

UIAlertController在IOS8中新加的，整合了UIAlertView和UIActionSheet兩個控件

UIAlertView和UIActionSheet在IOS9中已經廢棄

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1.兩種表現形式：UIAlertControllerStyle

UIAlertControllerStyleAlert
UIAlertControllerStyleActionSheet

2. UIAlertControllerStyleAlert(UIAlertView)

//初始化UIAlertController
  UIAlertController *alert = [UIAlertController alertControllerWithTitle:nil message:@"請輸入message" preferredStyle:UIAlertControllerStyleAlert];

  //建立點擊按鈕
  UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:nil];
    UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
        //添加點擊事件
    }

    //添加按鈕到UIAlertController
    [alert addAction:cancelAction];
    [alert addAction:okAction];

    [self presentViewController:alert animated:YES completion:nil];

此外，還能夠在AlertView(僅限在當前模式，ActionSheet中不可用)中添加TextField，以下

//在畫面中添加TextField
    [alert addTextFieldWithConfigurationHandler:^(UITextField *textField) {

        //添加提示信息
        textField.placeholder = @"登錄,添加了監聽,輸入少於5個字符";
        
        // 消息通知機制(KVO): 監聽－－註冊通知
        [[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(textFileChange:) name:UITextFieldTextDidChangeNotification object:textField];
    }];

/** AlertView中TextField監聽*/
-(void)textFileChange:(NSNotification *)notification{
    UITextField *textField = (UITextField *)notification.object;
    
    UIAlertController *alert = (UIAlertController *)self.presentedViewController;
    
    UITextField *listen = alert.textFields[1];
    UIAlertAction *action = alert.actions.lastObject;
    //若是textFiled的長度超過5個字符，最後一個default按鈕點擊不可
    action.enabled = (listen.text.length <= 5);
}

3. UIAlertControllerStyleActionSheet(UIActionSheet)

//初始化
    UIAlertController *actionSheet = [UIAlertController alertControllerWithTitle:@"UIAlertControllerStyleActionSheet" message:@"Switched" preferredStyle:UIAlertControllerStyleActionSheet];
    
    //建立按鈕
    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:nil];
    UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action){
        //添加點擊事件
    }];

    //添加按鈕
    [actionSheet addAction:cancelAction];
    [actionSheet addAction:okAction];
    
    [self presentViewController:actionSheet animated:YES completion:nil];