在iOS 8中使用UIAlertController

1 UIAlertView *alertview = [[UIAlertView alloc] initWithTitle:@"标题" message:@"这个是UIAlertView的默认样式" delegate:self cancelButtonTitle:@"取消" otherButtonTitles:@"好的", nil];
2 [alertview show];

1 var alertView = UIAlertView(title: "标题", message: "这个是UIAlertView的默认样式", delegate: self, cancelButtonTitle: "取消")
2 alertView.show()

1 var alertView = UIAlertView()
2 alertView.delegate = self
3 alertView.title = "标题"
4 alertView.message = "这个是UIAlertView的默认样式"
5 alertView.addButtonWithTitle("取消")
6 alertView.addButtonWithTitle("好的")
7 alertView.show()

1 UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"标题" message:@"这个是UIAlertController的默认样式" preferredStyle:UIAlertControllerStyleAlert];

1 var alertController = UIAlertController(title: "标题", message: "这个是UIAlertController的默认样式", preferredStyle: UIAlertControllerStyle.Alert)

1 UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:nil];
2 UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"好的" style:UIAlertActionStyleDefault handler:nil];
3 [alertController addAction:cancelAction];
4 [alertController addAction:okAction];

1 var cancelAction = UIAlertAction(title: "取消", style: UIAlertActionStyle.Cancel, handler: nil)
2 var okAction = UIAlertAction(title: "好的", style: UIAlertActionStyle.Default, handler: nil)
3 alertController.addAction(cancelAction)
4 alertController.addAction(okAction)

1 [self presentViewController:alertController animated:YES completion:nil];

self.presentViewController(alertController, animated: true, completion: nil)

1 UIAlertAction *resetAction = [UIAlertAction actionWithTitle:@"重置" style:UIAlertActionStyleDestructive handler:nil];
2 [alertController addAction:resetAction];

1 var resetAction = UIAlertAction(title: "重置", style: UIAlertActionStyle.Destructive, handler: nil)
2 alertController.addAction(resetAction)

1 UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"文本对话框" message:@"登录和密码对话框示例" preferredStyle:UIAlertControllerStyleAlert];
2 [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField){
3     textField.placeholder = @"登录";
4 }];
5 [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField) {
6     textField.placeholder = @"密码";
7     textField.secureTextEntry = YES;
8 }];

1 alertController.addTextFieldWithConfigurationHandler { 
2 (textField: UITextField!) -> Void in
3     textField.placeholder = "登录"
4 }
5 alertController.addTextFieldWithConfigurationHandler { 
6 (textField: UITextField!) -> Void in
7     textField.placeholder = "密码"
8     textField.secureTextEntry = true
9 }

1 UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"好的" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
2     UITextField *login = alertController.textFields.firstObject;
3     UITextField *password = alertController.textFields.lastObject;
4     ...
5 }];

1 var okAction = UIAlertAction(title: "好的", style: UIAlertActionStyle.Default) {
2 (action: UIAlertAction!) -> Void in
3     var login = alertController.textFields?.first as UITextField
4     var password = alertController.textFields?.last as UITextField
5 }

1 [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField){
2     ...
3     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(alertTextFieldDidChange:) name:UITextFieldTextDidChangeNotification object:textField];
4 }];

1 alertController.addTextFieldWithConfigurationHandler {
2 (textField: UITextField!) -> Void in
3     ...
4     NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("alertTextFieldDidChange:"), name: UITextFieldTextDidChangeNotification, object: textField)
5 }

1 UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"好的" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
2     ...
3     [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidChangeNotification object:nil];
4 }];

1 alertController.addTextFieldWithConfigurationHandler {
2 (textField: UITextField!) -> Void in
3     ...
4     NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("alertTextFieldDidChange:"), name: UITextFieldTextDidChangeNotification, object: textField)
5 }

1 UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"好的" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
2     ...
3     [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidChangeNotification object:nil];
4 }];

1 var okAction = UIAlertAction(title: "好的", style: UIAlertActionStyle.Default) {
2 (action: UIAlertAction!) -> Void in
3     ...
4     NSNotificationCenter.defaultCenter().removeObserver(self, name: UITextFieldTextDidChangeNotification, object: nil)
5 }

1 okAction.enabled = NO;

1 okAction.enabled = false

1 - (void)alertTextFieldDidChange:(NSNotification *)notification{
2     UIAlertController *alertController = (UIAlertController *)self.presentedViewController;
3     if (alertController) {
4         UITextField *login = alertController.textFields.firstObject;
5         UIAlertAction *okAction = alertController.actions.lastObject;
6         okAction.enabled = login.text.length > 2;
7     }
8 }

1 func alertTextFieldDidChange(notification: NSNotification){
2     var alertController = self.presentedViewController as UIAlertController?
3     if (alertController != nil) {
4         var login = alertController!.textFields?.first as UITextField
5         var okAction = alertController!.actions.last as UIAlertAction
6         okAction.enabled = countElements(login.text) > 2
7     }
8 }

1 UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"保存或删除数据" message:@"删除数据将不可恢复" preferredStyle: UIAlertControllerStyleActionSheet];

swift版本：

1 var alertController = UIAlertController(title: "保存或删除数据", message: "删除数据将不可恢复", preferredStyle: UIAlertControllerStyle.ActionSheet)

添加按钮动作的方式和对话框相同。

Objective-C版本：

1 UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:nil];
2 UIAlertAction *deleteAction = [UIAlertAction actionWithTitle:@"删除" style:UIAlertActionStyleDestructive handler:nil];
3 UIAlertAction *archiveAction = [UIAlertAction actionWithTitle:@"保存" style:UIAlertActionStyleDefault handler:nil];
4 [alertController addAction:cancelAction];
5 [alertController addAction:deleteAction];
6 [alertController addAction:archiveAction];

swift版本：

1 var cancelAction = UIAlertAction(title: "取消", style: UIAlertActionStyle.Cancel, handler: nil)
2 var deleteAction = UIAlertAction(title: "删除", style: UIAlertActionStyle.Destructive, handler: nil)
3 var archiveAction = UIAlertAction(title: "保存", style: UIAlertActionStyle.Default, handler: nil)
4 alertController.addAction(cancelAction)
5 alertController.addAction(deleteAction)
6 alertController.addAction(archiveAction)

您不能在上拉菜单中添加文本框，如果您强行作死添加了文本框，那么就会荣幸地得到一个运行时异常：

* Terminating app due to uncaught exception ‘NSInternalInconsistencyException’, reason: ‘Text fields can only be added to an alert controller of style UIAlertControllerStyleAlert’

同样，简单的异常说明，我们也不多说了。

接下来我们就可以在iPhone或者其他紧缩宽度的设备上展示了，不出我们所料，运行得很成功。

Objective-C版本：

1 [self presentViewController:alertController animated:YES completion:nil];

swift版本：

1 self.presentViewController(alertController, animated: true, completion: nil)

iPhone上的上拉菜单效果

如果上拉菜单中有“取消”按钮的话，那么它永远都会出现在菜单的底部，不管添加的次序是如何（就是这么任性）。其他的按钮将会按照添加的次序从上往下依次显示。《iOS 用户界面指南》要求所有的“毁坏”样式按钮都必须排名第一（红榜嘛，很好理解的，对不对？）。

别激动得太早，我们现在还有一个很严重的问题，这个问题隐藏得比较深。当我们使用iPad或其他常规宽度的设备时，就会得到一个运行时异常：

Terminating app due to uncaught exception ‘NSGenericException’, reason: ‘UIPopoverPresentationController (<_uialertcontrolleractionsheetregularpresentationcontroller: 0x7fc619588110="">) should have a non-nil sourceView or barButtonItem set before the presentation occurs.’

就如我们之前所说，在常规宽度的设备上，上拉菜单是以弹出框的形式展现。弹出框必须要有一个能够作为源视图或者栏按钮项目的描点(anchor point)。由于在本例中我们是使用了常规的UIButton来触发上拉菜单的，因此我们就将其作为描点。

在iOS 8中我们不再需要小心翼翼地计算出弹出框的大小，UIAlertController将会根据设备大小自适应弹出框的大小。并且在iPhone或者紧缩宽度的设备中它将会返回nil值。配置该弹出框的代码如下：

Objective-C版本：

1 UIPopoverPresentationController *popover = alertController.popoverPresentationController;
2 if (popover){
3     popover.sourceView = sender;
4     popover.sourceRect = sender.bounds;
5     popover.permittedArrowDirections = UIPopoverArrowDirectionAny;
6 }

swift版本：

1 var popover = alertController.popoverPresentationController
2 if (popover != nil){
3     popover?.sourceView = sender
4     popover?.sourceRect = sender.bounds
5     popover?.permittedArrowDirections = UIPopoverArrowDirection.Any
6 }

iPad上的上拉菜单效果

UIPopoverPresentationController类同样也是在iOS 8中新出现的类，用来替换UIPopoverController的。这个时候上拉菜单是以一个固定在源按钮上的弹出框的形式显示的。

要注意UIAlertController在使用弹出框的时候自动移除了取消按钮。用户通过点击弹出框的外围部分来实现取消操作，因此取消按钮便不再必需。

释放对话框控制器

通常情况下，当用户选中一个动作后对话框控制器将会自行释放。不过您仍然可以在需要的时候以编程方式释放它，就像释放其他视图控制器一样。您应当在应用程序转至后台运行时移除对话框或者上拉菜单。假定我们正在监听UIApplicationDidEnterBackgroundNotification通知消息，我们可以在observer中释放任何显示出来的视图控制器。（参考在viewDidLoad方法中设立observer的示例代码）。

Objective-C版本：

1 - (void)didEnterBackground:(NSNotification *)notification
2 {
3   [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidChangeNotification object:nil];
4   [self.presentedViewController dismissViewControllerAnimated:NO completion:nil];
5 }

swift版本：

1 func didEnterackground(notification: NSNotification){
2     NSNotificationCenter.defaultCenter().removeObserver(self, name: UITextFieldTextDidChangeNotification, object: nil)
3     self.presentedViewController?.dismissViewControllerAnimated(false, completion: nil)
4 }

注意，要保证运行安全我们同样要确保移除所有的文本框observer。

我们来总结一下

这篇文章比较长，但是希望能够对您有所帮助。原先的UIAlertView和UIActionSheet类仍然可以在iOS 8中工作得很好，所以没有必要急于更换代码（要知道本文用到的许多函数尽在iOS 8中支持）。