iPhone UIDatePicker 非常慢

Question

我在 ModeTime 上使用 UIDatePicker，

但速度很慢？

这里是代码：

#import "U2YAccountController.h"

@implementation U2YAccountController
@synthesize timePicker = _timePicker;
@synthesize timeLabel= _timeLabel;  
@synthesize scheduleLabel = _scheduleLabel;

- (id)init
{
self = [super init];
if (self) {
    // Set title
    self.title = @"Reminder Settings"; 


    CGRect dosageImageRect = CGRectMake(10, 30, 300, 62);
    UIImageView *dosageImage = [[UIImageView alloc] initWithFrame:dosageImageRect];
    [dosageImage setImage:[UIImage imageNamed:@"dosageReminderButton.png"]]; //image was a button, now just image change name of png!
    dosageImage.opaque = YES; // explicitly opaque for performance
    [self.view addSubview:dosageImage];
    [dosageImage release];




    UIButton *timeReminderButton = [UIButton buttonWithType:UIButtonTypeCustom];
    [timeReminderButton setImage:[UIImage imageNamed:@"reminderTimeButton.png"] forState:UIControlStateNormal]; 
    [timeReminderButton setFrame:CGRectMake(10, 110, 300, 44)];
    [timeReminderButton addTarget:self action:@selector(timeReminderButtonPressed:) forControlEvents:UIControlEventTouchUpInside];
    [timeReminderButton setAdjustsImageWhenHighlighted:NO];
    [self.view addSubview:timeReminderButton];


    self.timePicker = [[[UIDatePicker alloc] initWithFrame:CGRectMake(0, 415, 220, 180)]autorelease];
    self.timePicker.datePickerMode = UIDatePickerModeTime;
    [self.timePicker addTarget:self action:@selector(timePickerChanged:) forControlEvents:UIControlEventValueChanged];
    [self.view addSubview:self.timePicker];
    //[self.timePicker setHidden:YES];

    self.scheduleLabel = [[[UILabel alloc]initWithFrame:CGRectMake(22, 64, 200, 20)]autorelease];
    self.scheduleLabel.textColor = [UIColor colorWithRed:12/255.0 green:113/255.0 blue:186/255.0 alpha:1];
    self.scheduleLabel.text = @"Schedule 6 of 7 days";  //updated from web site!!
    [self.view addSubview:self.scheduleLabel];

    self.timeLabel = [[[UILabel alloc]initWithFrame:CGRectMake(213, 122, 80, 20)]autorelease];
    self.timeLabel.textColor = [UIColor colorWithRed:12/255.0 green:113/255.0 blue:186/255.0 alpha:1];
    self.timeLabel.backgroundColor = [UIColor clearColor];
    self.timeLabel.text = @"";
    [self.view addSubview:self.timeLabel];


    dateFormat = [[NSDateFormatter alloc] init];
    [dateFormat setDateFormat:@"hh:mma"];

}
return self;
}


 - (void) timeReminderButtonPressed :(id) sender {


recognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewTapped:)] ;


[UIView beginAnimations:@"PickerUp" context:nil];
[UIView setAnimationDuration:0.3f];
[UIView setAnimationBeginsFromCurrentState:YES];

self.timePicker.frame = CGRectMake(0, 237, 320, 180);

[self.view addGestureRecognizer:recognizer];

[recognizer release];



}

- (void) timePickerChanged:(id) sender {


today = [sender date];


NSString *dateString = [dateFormat stringFromDate:today];

self.timeLabel.text = dateString;


}

- (void) viewTapped :(id) sender {
[UIView beginAnimations:@"PickerDown" context:nil];
[UIView setAnimationDuration:0.3f];
[UIView setAnimationBeginsFromCurrentState:YES];

self.timePicker.frame = CGRectMake(0, 415, 320, 180);

[self.view removeGestureRecognizer:recognizer];

}


- (void) dealloc {

[dateFormat release];


[_scheduleLabel release];
[_timeLabel release];
[_timePicker release];
[super dealloc];
}

@end

那么为什么我的选择器很慢并且卡住了？ 我错过了什么？

附：我已经评论了 nsDateFormatter 以查找这是否是问题所在，但没有改变......

非常感谢！

Answer 1

我最初的反应：

分配一个 NSDateFormatter 并不是一个便宜的前景。在您的情况下，您一遍又一遍地使用相同的格式字符串，因此您应该真正分配一个 NSDateFormatter，将其保存为实例变量，然后在 >UIDatePicker 操作触发。这应该会大大加快速度。

Answer 2

要添加到之前的答案的另一件事是您忘记提交动画。我什至建议您使用 UIView 类的 animateWith... 方法而不是 beginAnimation/commitAnimation ，因为它应该更快（至少苹果如此）。
还有一件事要走。手势识别器...为什么不在初始化时使用视图创建它？为什么每次调用选择器时都要创建它？