UIAlertController

UIAlertController
iOS2.0之后，使用UIAlertView来设置提示框，使用initWithTitle:message: delegate:self cancelButtonTitle:otherButtonTitles:初始化alertView，然后使用-show显示alert。如果想获取button则需要使用delegate方法。(UIActionSheet类似)
在IOS8之后，UIAlertController替代了UIActionSheet和UIAlertView。是UIViewController的子类，它使用工厂方法，利用preferredStyle属性，暂时提供alert以及actionSheet（实际使用时，使用alertControllerWithTitle:message:preferredStyle中preferredStyle即可制定提示框的类型）。
注意，
(1) 这个class不能通过继承的方式来自定义。
(2)UIAlertController必须等到View Controller加载后才能显示，如果将UIAlertController类写在View Controller中没有效果。

1、下面是常用的属性和方法

//在actionWithTitle:Style:handler中的style参数，设置按钮的styletypedef NS_ENUM(NSInteger, UIAlertActionStyle) {    UIAlertActionStyleDefault = 0,    UIAlertActionStyleCancel,//取消    UIAlertActionStyleDestructive//销毁,红色的字体} NS_ENUM_AVAILABLE_IOS(8_0);//alertControllerWithTitle:message:preferredStyle:初始化UIAlertController时,perferredStyle的参数，表示信息框是ActionSheet还是Alert。typedef NS_ENUM(NSInteger, UIAlertControllerStyle) {    UIAlertControllerStyleActionSheet = 0,    UIAlertControllerStyleAlert} NS_ENUM_AVAILABLE_IOS(8_0);@interface UIAlertAction : NSObject <NSCopying>＋(instancetype)actionWithTitle:(nullable NSString *)title style:(UIAlertActionStyle)style handler:(void (^ __nullable)(UIAlertAction *action))handler;@property (nullable, nonatomic, readonly) NSString *title;@property (nonatomic, readonly) UIAlertActionStyle style;@property (nonatomic, getter=isEnabled) BOOL enabled;@end@interface UIAlertController : UIViewController＋(instancetype)alertControllerWithTitle:(nullable NSString *)title message:(nullable NSString *)message preferredStyle:(UIAlertControllerStyle)preferredStyle;//添加向controller中添加action- (void)addAction:(UIAlertAction *)action;@property (nonatomic, readonly) NSArray<UIAlertAction *> *actions;@property (nonatomic, strong, nullable) UIAlertAction *preferredAction NS_AVAILABLE_IOS(9_0);//添加文本框- (void)addTextFieldWithConfigurationHandler:(void (^ __nullable)(UITextField *textField))configurationHandler;@property (nullable, nonatomic, readonly) NSArray<UITextField *> *textFields;//获取所有的文本框@property (nullable, nonatomic, copy) NSString *title;@property (nullable, nonatomic, copy) NSString *message;@property (nonatomic, readonly) UIAlertControllerStyle preferredStyle;@end

2、例子：使用警示框输入账户、密码，实现登录。

-(void)AlertAchieveLogin{    //1、初始化UIAlertController    /*     +alertControllerWithTitle:message:preferredStyle:声明     title:UIAlertController的标题     message:title下面的解释文字     preferredStyle:AlertController是Alert还是ActionSheet     */    UIAlertController *controller = [UIAlertController alertControllerWithTitle:@"登录" message:@"请输入姓名和密码" preferredStyle:UIAlertControllerStyleAlert];    //2、UIAlertAction设置按钮    //取消按钮,alert信息框消失    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {        [self dismissViewControllerAnimated:YES completion:nil];    }];    //登录按钮    /*     +actionWithTitle:style:handler:     title:action的标题     style:alertAction的风格,UIAlertActionStyleDefault,UIAlertActionStyleCancel,UIAlertActionStyleDestructive     handler:处理用户按下该按钮后要做的操作     */    UIAlertAction *loginAction = [UIAlertAction actionWithTitle:@"登录" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {        //点击登录按钮后,获取账户和密码        NSString *account = [controller.textFields objectAtIndex:0].text;        NSString *pwd = [controller.textFields objectAtIndex:1].text;        NSLog(@"账户是:%@,密码:%@",account,pwd);    }];    //3、向UIAlertController添加按钮    [controller addAction:cancelAction];    [controller addAction:loginAction];    //4、设置文本框    [controller addTextFieldWithConfigurationHandler:^(UITextField * _Nonnull textField) {        //在文本框中,显示account        textField.placeholder = @"account";        textField.layer.masksToBounds = YES;        textField.layer.cornerRadius  = 10;        textField.backgroundColor = [UIColor lightGrayColor];    }];    [controller addTextFieldWithConfigurationHandler:^(UITextField * _Nonnull textField) {        //在文本框中,显示password        textField.placeholder = @"password";        textField.layer.masksToBounds = YES;        textField.layer.cornerRadius  = 10;    }];    //5、展示信息框    //使用presentViewController:animated:completion:呈现alertController    [self presentViewController:controller animated:YES completion:nil];}