iphone – XCode：当用户点击UITextbox时显示UIDatePicker

我注意到你的代码中遇到的第一个问题之一是,对于那些刚接触iOS / Mac开发的人来说,这是一个非常常见的问题,就是你试图设置一个尚不存在的对象的属性.放“self.dueDate.inputView = datePicker;”在你的initWithNibName：bundle中：因为视图尚未加载而无法工作,dueDate是你视图的一部分.在objective-c中,使用alloc& amp;来实例化一个对象.在里面. Init是对任何对象的第一个实际方法调用.此时,在视图控制器的生命周期中,尚未创建视图.方法调用self.dueDate.inputView = datePicker;属于viewDidLoad方法.当它听起来像是被调用的时候会被调用,并且您的dueDate属性将在该点被正确加载.无需使用UITextField的自定义子类来显示文本字段的日期选择视图.以下是自定义输入视图类的一个非常基本的示例：

ExampleBasicDateInputView.h：

#import <UIKit/UIKit.h>

@interface ExampleBasicDateInputView : UIView
@property (strong,nonatomic) UIDatePicker *datePicker;
@end

ExampleBasicDateInputView.m：

#import "ExampleBasicDateInputView.h"

@implementation ExampleBasicDateInputView{
    UITextField *_inputField; // ivar to store the textfield currently being edited
}
@synthesize datePicker = _datePicker;
// TARGET METHODS
-(void)pickerValueChanged:(UIDatePicker *)picker{
    _inputField.text = self.datePicker.date.description; // set text to date description
}
-(void)viewDoubleTapped:(UITapGestureRecognizer *)tapGR{
    [_inputField resignFirstResponder]; // upon double-tap dismiss picker
}
-(void)textFieldBeganEditing:(NSNotification *)note{
    _inputField = note.object; // set ivar to current first responder
}
-(void)textFieldEndedEditing:(NSNotification *)note{
    _inputField = nil; // the first responder ended editing CRITICAL:avoids retain cycle
}
// INITI METHODS
-(void)initializationCodeMethod{
    _datePicker = [[UIDatePicker alloc] initWithFrame:CGRectMake(0,0)];// All pickers have preset height
    self.bounds = _datePicker.frame; // Make our view same size as picker
    [self addSubview:_datePicker];
    [_datePicker addTarget:self action:@selector(pickerValueChanged:) forControlEvents:UIControlEventValueChanged]; // register to be notified when the value changes
        // As an example we'll use a tap gesture recognizer to dismiss on a double-tap
    UITapGestureRecognizer *tapGR = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewDoubleTapped:)];
    tapGR.numberOfTapsRequired = 2; // Limit to double-taps
    [self addGestureRecognizer:tapGR];
    NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
    [center addObserver:self selector:@selector(textFieldBeganEditing:) name:UITextFieldTextDidBeginEditingNotification object:nil]; // Ask to be informed when any textfield begins editing
    [center addObserver:self selector:@selector(textFieldEndedEditing:) name:UITextFieldTextDidEndEditingNotification object:nil]; // Ask to be informed when any textfield ends editing
}
-(id)init{
    if ((self = [super init])){
        [self initializationCodeMethod];
    }
    return self;
}
-(id)initWithFrame:(CGRect)frame{
    if ((self = [super initWithFrame:frame])){
        [self initializationCodeMethod];
    }
    return self;
}
-(id)initWithCoder:(NSCoder *)aDecoder{
    if ((self = [super initWithCoder:aDecoder])){
        [self initializationCodeMethod];
    }
    return self;
}
-(void)dealloc{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidBeginEditingNotification object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidEndEditingNotification object:nil];
}
@end

然后在视图中加载你将使用这样的类：

ExampleBasicDateInputView *dateEntryView = [[ExampleBasicDateInputView alloc] init];
self.dueDate.inputView = datePickerView;

正如您在.h文件中看到的那样,我们已将日期选择器实例公开为属性,因此您可以设置样式.等等：

dateEntryView.datePicker.datePickerMode = UIDatePickerModeDate;

显然这是一个非常基本的例子,但我认为它显示了可以做的事情.