iOS8下的UIAlertContoller初探

iOS8推出了几个新的“controller”，主要是把类似之前的UIAlertView变成了UIAlertController，这不经意的改变，貌似把我之前理解的“controller”一下子推翻了～但是也无所谓，有新东西不怕，学会使用了就行。接下来会探讨一下这些个新的Controller。

- (void)showOkayCancelAlert {
    NSString *title = NSLocalizedString(@"A Short Title Is Best", nil);
    NSString *message = NSLocalizedString(@"A message should be a short, complete sentence.", nil);
    NSString *cancelButtonTitle = NSLocalizedString(@"Cancel", nil);
    NSString *otherButtonTitle = NSLocalizedString(@"OK", nil);

    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];
    
    // Create the actions.
    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:cancelButtonTitle style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
        NSLog(@"The \"Okay/Cancel\" alert's cancel action occured.");
    }];
    
    UIAlertAction *otherAction = [UIAlertAction actionWithTitle:otherButtonTitle style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
        NSLog(@"The \"Okay/Cancel\" alert's other action occured.");
    }];
    
    // Add the actions.
    [alertController addAction:cancelAction];
    [alertController addAction:otherAction];
    
    [self presentViewController:alertController animated:YES completion:nil];
}

这是最普通的一个alertcontroller，一个取消按钮，一个确定按钮。

新的alertcontroller，其初始化方法也不一样了，按钮响应方法绑定使用了block方式，有利有弊。需要注意的是不要因为block导致了引用循环，记得使用__weak，尤其是使用到self。

上面的界面如下：

iOS8下的UIAlertContoller初探

如果UIAlertAction *otherAction这种otherAction多几个的话，它会自动排列成如下：

iOS8下的UIAlertContoller初探

另外，很多时候，我们需要在alertcontroller中添加一个输入框，例如输入密码：

iOS8下的UIAlertContoller初探

这时候可以添加如下代码：

 [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField) {
        // 可以在这里对textfield进行定制，例如改变背景色
        textField.backgroundColor = [UIColor orangeColor];
    }];

而改变背景色会这样：

iOS8下的UIAlertContoller初探

完整的密码输入：

- (void)showSecureTextEntryAlert {
    NSString *title = NSLocalizedString(@"A Short Title Is Best", nil);
    NSString *message = NSLocalizedString(@"A message should be a short, complete sentence.", nil);
    NSString *cancelButtonTitle = NSLocalizedString(@"Cancel", nil);
    NSString *otherButtonTitle = NSLocalizedString(@"OK", nil);

    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];
    
    // Add the text field for the secure text entry.
    [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField) {
        // Listen for changes to the text field's text so that we can toggle the current
        // action's enabled property based on whether the user has entered a sufficiently
        // secure entry.
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleTextFieldTextDidChangeNotification:) name:UITextFieldTextDidChangeNotification object:textField];

        textField.secureTextEntry = YES;
    }];

    // Create the actions.
    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:cancelButtonTitle style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
        NSLog(@"The \"Secure Text Entry\" alert's cancel action occured.");

        // Stop listening for text changed notifications.
        [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidChangeNotification object:alertController.textFields.firstObject];
    }];

    UIAlertAction *otherAction = [UIAlertAction actionWithTitle:otherButtonTitle style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
        NSLog(@"The \"Secure Text Entry\" alert's other action occured.");

        // Stop listening for text changed notifications.
        [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidChangeNotification object:alertController.textFields.firstObject];
    }];
    
    // The text field initially has no text in the text field, so we'll disable it.
    otherAction.enabled = NO;

    // Hold onto the secure text alert action to toggle the enabled/disabled state when the text changed.
    self.secureTextAlertAction = otherAction;

    // Add the actions.
    [alertController addAction:cancelAction];
    [alertController addAction:otherAction];
    
    [self presentViewController:alertController animated:YES completion:nil];
}

注意四点：

1.添加通知，监听textfield内容的改变：

// Add the text field for the secure text entry.
    [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField) {
        // Listen for changes to the text field's text so that we can toggle the current
        // action's enabled property based on whether the user has entered a sufficiently
        // secure entry.
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleTextFieldTextDidChangeNotification:) name:UITextFieldTextDidChangeNotification object:textField];

        textField.secureTextEntry = YES;
    }];

2.初始化时候，禁用“ok”按钮：

otherAction.enabled = NO;

self.secureTextAlertAction = otherAction;//定义一个全局变量来存储

3.当输入超过5个字符时候，使self.secureTextAlertAction ＝ YES：

- (void)handleTextFieldTextDidChangeNotification:(NSNotification *)notification {
    UITextField *textField = notification.object;

    // Enforce a minimum length of >= 5 characters for secure text alerts.
    self.secureTextAlertAction.enabled = textField.text.length >= 5;
}

4.在“OK”action中去掉通知：

UIAlertAction *otherAction = [UIAlertAction actionWithTitle:otherButtonTitle style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
        NSLog(@"The \"Secure Text Entry\" alert's other action occured.");

        // Stop listening for text changed notifications.
        [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidChangeNotification object:alertController.textFields.firstObject];
    }];

最后是以前经常是alertview与actionsheet结合使用，这里同样也有：

- (void)showOkayCancelActionSheet {
    NSString *cancelButtonTitle = NSLocalizedString(@"Cancel", nil);
    NSString *destructiveButtonTitle = NSLocalizedString(@"OK", nil);
    
    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:nil message:nil preferredStyle:UIAlertControllerStyleActionSheet];
    
    // Create the actions.
    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:cancelButtonTitle style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
        NSLog(@"The \"Okay/Cancel\" alert action sheet's cancel action occured.");
    }];
    
    UIAlertAction *destructiveAction = [UIAlertAction actionWithTitle:destructiveButtonTitle style:UIAlertActionStyleDestructive handler:^(UIAlertAction *action) {
        NSLog(@"The \"Okay/Cancel\" alert action sheet's destructive action occured.");
    }];
    
    // Add the actions.
    [alertController addAction:cancelAction];
    [alertController addAction:destructiveAction];
    
    [self presentViewController:alertController animated:YES completion:nil];
}