iOS开发_7_UITextField

UIResponder

UIResponder是UIkit框架中的一个抽象类，其定义了一系列方法，用于接收和处理用户事件，例如触摸事件、运动事件（摇晃设备）和功能控制事件（编辑文本或播放音乐）等。UIResponder的子类会覆盖这些方法。

UIWindow有一个firstResponder属性指向第一响应者。例如，当用户点击UITextField对象时，UITextfield对象就会成为第一响应者。UIWindow会将firstResponder指向该对象，之后，如果应用接收到运动事件和功能控制事件，都会发送给UITextField对象。

当某个UITextField对象或者UITextView对象成为第一响应者时，屏幕会弹出键盘。除了用户点击外，还可以在代码中向UITextField对象发送becomeFirstResponser消息，使其成为第一响应者。如果要关闭键盘，则可以向UITextField对象发送resignFirstResponder消息。

设置UITextField的键盘

UITextField的几个属性

  • autocapitalizationType：设置UITextField对象的自动大写功能，包括none、words（单词）、sentence、allcharacter（所有字母）

  • autocorrectionType：启用/禁用（设置为YES/NO，下同）UITextField对象的拼写建议功能

  • enablesReturnKeyAutomatically：启用/禁用UITextField对象的换行键自动检测功能，如果将该属性设置为YES，UITextField对象会自动检测用户输入，并根据是否输入文字启用/禁用换行键

  • keyboardType：设置UITextField对象弹出键盘类型，例如ASCII Capble（ASCII标准键盘）、E-Mail Address（电子邮件地址）、Number pad（数字键盘）和URL（网址）

  • secureTextEntry：启用/禁用UITextField对象的安全输入功能，如果将该属性设置为YES、UITextField对象会以原点代替用户输入的文字，常见于密码输入框

委托

UITextField对象具有一个委托属性，通过UITextField对象设置委托，UiTextField对象会在发生事件时向委托发送相应的消息，由委托处理该事件。

对于编辑UiTextField对象文本内容的事件，有以下两个对应的委托方法：

-(void) textFieldDidEndEditing: (UITextField *) textField;

-(void) textFieldDidBeginEditing: (UITextField *) textField;

还有带返回值的委托方法，用于从委托中查询需要的信息

-(void) textFieldShouldEndEditing: (UITextField *) textField;

-(void) textFieldShouldBeginEditing: (UITextField *) textField;

-(void) textFieldShouldClear: (UITextField *) textField;

-(void) textFieldShouldReturn: (UITextField *) textField;

注意，在委托方法中，通常应该将对象自身作为第一个参数。

多个对象可能具有相同的委托，当委托收到消息时，需要根据该参数判断发送给该消息的对象。例如，某个控制器中包含多个UITextField对象，他们的委托都是该控制器，那么控制器要根据TextField参数获取相应的UITextField对象并执行不同操作。

协议

凡是支持委托的对象，其背后都有一个相应的协议，声明可以向该对象的委托对象发送的消息。被委托对象需要根据这个协议为其“感兴趣”的事件实现相应的方法。如果一个类实现了某个协议中规定的方法，称这个类遵守协议。

UITextField的协议：

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@protocol UITextFieldDelegate <NSObject>

@optional

- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField;        // return NO to disallow editing.
- (void)textFieldDidBeginEditing:(UITextField *)textField;           // became first responder
- (BOOL)textFieldShouldEndEditing:(UITextField *)textField;          // return YES to allow editing to stop and to resign first responder status. NO to disallow the editing session to end
- (void)textFieldDidEndEditing:(UITextField *)textField;             // may be called if forced even if shouldEndEditing returns NO (e.g. view removed from window) or endEditing:YES called
- (void)textFieldDidEndEditing:(UITextField *)textField reason:(UITextFieldDidEndEditingReason)reason NS_AVAILABLE_IOS(10_0); // if implemented, called in place of textFieldDidEndEditing:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string;   // return NO to not change text

- (BOOL)textFieldShouldClear:(UITextField *)textField;               // called when clear button pressed. return NO to ignore (no notifications)
- (BOOL)textFieldShouldReturn:(UITextField *)textField;              // called when 'return' key pressed. return NO to ignore.

@end

发送方在发送可选方法前，会先向其委托发送另一个名为respondsToSelector：方法。

所有objective-c对象都从NSObject继承了respondToSelector：方法，该方法能在运行时检查对象是否实现了指定的方法。

@selector()指令可以将选择器(selector)转换成数值，以便将其作为参数进行传递。

例如，UITextField可以实现如下方法

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- (void)clearButtonTapped
{
	//textFieldshouldClear:是可选方法，需要检查委托是否实现了该方法
	SEL clearAelector = @selector(textFieldShouldClear);
	if([self.delegate respondsToSelector:clearSelector]){
		if([self.delegate textFieldShouldClear:self]){
			self.text = @"";
		}
	}
}

iOS SDK很多类都具有委托，几乎所有的委托都是弱引用（weak）；这是为了避免对象及其委托之间产生强引用循环。

向屏幕中添加UILabel对象

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- (void)drawHypnoticMessage:(NSString *)message
{
    for (int i = 0; i < 20; i++) {
        UILabel *messageLabel = [[UILabel alloc] init];

        // Configure the label's colors and text
        messageLabel.backgroundColor = [UIColor clearColor];
        messageLabel.textColor = [UIColor whiteColor];
        messageLabel.text = message;

        // This method resizes the label, which will be relative
        // to the text that it is displaying
        [messageLabel sizeToFit];

        // Get a random x value that fits within the hypnosis view's width
        int width = self.view.bounds.size.width - messageLabel.bounds.size.width;
        int x = arc4random_uniform(width);

        // Get a random y value that fits within the hypnosis view's height
        int height = self.view.bounds.size.height - messageLabel.bounds.size.height;
        int y = arc4random_uniform(height);

        // Update the label's frame
        CGRect frame = messageLabel.frame;
        frame.origin = CGPointMake(x, y);
        messageLabel.frame = frame;

        // Add the label to the hierarchy
        [self.view addSubview:messageLabel];
        //添加视差效果
        UIInterpolatingMotionEffect *motionEffect;
        motionEffect = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:@"center.x"
                                                                       type:UIInterpolatingMotionEffectTypeTiltAlongHorizontalAxis];
        motionEffect.minimumRelativeValue = @-25;
        motionEffect.maximumRelativeValue = @25;
        [messageLabel addMotionEffect:motionEffect];

        motionEffect = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:@"center.y"
                                                                       type:UIInterpolatingMotionEffectTypeTiltAlongVerticalAxis];
        motionEffect.minimumRelativeValue = @-25;
        motionEffect.maximumRelativeValue = @25;
        [messageLabel addMotionEffect:motionEffect];
    }
}

附：

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//  BNRHypnosisViewController.m

#import "BNRHypnosisViewController.h"
#import "BNRHypnosisView.h"

@interface BNRHypnosisViewController () <UITextFieldDelegate>

@end

@implementation BNRHypnosisViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {

        // Set the tab bar item's title
        self.tabBarItem.title = @"Hypnotize";

        // Create a UIImage from a file
        // This will use Hypno@2x on retina display devices
        UIImage *image = [UIImage imageNamed:@"Hypno.png"];

        // Put that image on the tab bar item
        self.tabBarItem.image = image;
    }

    return self;
}

- (void)loadView
{
    // Create a view
    CGRect frame = [UIScreen mainScreen].bounds;
    BNRHypnosisView *backgroundView = [[BNRHypnosisView alloc] initWithFrame:frame];

    CGRect textFieldRect = CGRectMake(40, 70, 240, 30);
    UITextField *textField = [[UITextField alloc] initWithFrame:textFieldRect];

    // Setting the border style on the text field will allow us to see it easier
    textField.borderStyle = UITextBorderStyleRoundedRect;
    textField.placeholder = @"Hypnotize me";
    textField.returnKeyType = UIReturnKeyDone;
    [backgroundView addSubview:textField];

    textField.delegate = self;

    // Set it as *the* view of this view controller
    self.view = backgroundView;
}

- (void)viewDidLoad
{
    // Always call the super implementation of viewDidLoad
    [super viewDidLoad];

    NSLog(@"BNRHypnosisViewController loaded its view");
}

- (BOOL)textFieldShouldReturn:(UITextField *)textField
{
    [self drawHypnoticMessage:textField.text];

    textField.text = @"";
    [textField resignFirstResponder];

    return YES;
}

- (void)drawHypnoticMessage:(NSString *)message
{
    for (int i = 0; i < 20; i++) {
        UILabel *messageLabel = [[UILabel alloc] init];

        // Configure the label's colors and text
        messageLabel.backgroundColor = [UIColor clearColor];
        messageLabel.textColor = [UIColor whiteColor];
        messageLabel.text = message;

        // This method resizes the label, which will be relative
        // to the text that it is displaying
        [messageLabel sizeToFit];

        // Get a random x value that fits within the hypnosis view's width
        int width = self.view.bounds.size.width - messageLabel.bounds.size.width;
        int x = arc4random_uniform(width);

        // Get a random y value that fits within the hypnosis view's height
        int height = self.view.bounds.size.height - messageLabel.bounds.size.height;
        int y = arc4random_uniform(height);

        // Update the label's frame
        CGRect frame = messageLabel.frame;
        frame.origin = CGPointMake(x, y);
        messageLabel.frame = frame;

        // Add the label to the hierarchy
        [self.view addSubview:messageLabel];

        UIInterpolatingMotionEffect *motionEffect;
        motionEffect = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:@"center.x"
                                                                       type:UIInterpolatingMotionEffectTypeTiltAlongHorizontalAxis];
        motionEffect.minimumRelativeValue = @-25;
        motionEffect.maximumRelativeValue = @25;
        [messageLabel addMotionEffect:motionEffect];

        motionEffect = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:@"center.y"
                                                                       type:UIInterpolatingMotionEffectTypeTiltAlongVerticalAxis];
        motionEffect.minimumRelativeValue = @-25;
        motionEffect.maximumRelativeValue = @25;
        [messageLabel addMotionEffect:motionEffect];
    }
}

@end
iOS

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