当我的应用程序从后台运行返回时 UIButton 消失

Question

我有一个小项目，其中包含一些带有数字键盘的 UITextField。当显示键盘时，我正在添加一个按钮作为子视图，供用户关闭键盘。

但是，如果键盘处于活动状态并且我关闭了应用程序，我添加的按钮将在重新启动应用程序时消失。 （应用程序通过多任务处理保持非活动状态，因此不会完全退出。）

这是我用来添加按钮的代码（我在 xib 中配置的“完成”按钮）。

- (void)viewDidLoad
{
    [[NSNotificationCenter defaultCenter] addObserver:self
    selector:@selector(keyboardWillShow)name:UIKeyboardWillShowNotification object:nil];

    [super viewDidLoad];
}

- (void)keyboardWillShow{
    [[NSNotificationCenter defaultCenter] removeObserver:self];

    // We must perform on delay (schedules on next run loop pass) for the keyboard subviews to be present.
    [self performSelector:@selector(addHideKeyboardButtonToKeyboard) withObject:nil afterDelay:0]; 
}

- (void)addHideKeyboardButtonToKeyboard{
    // Locate non-UIWindow.
    doneButton.hidden=NO;

    UIWindow *keyboardWindow = nil;
    for (UIWindow *testWindow in [[UIApplication sharedApplication] windows]) {
        if (![[testWindow class] isEqual:[UIWindow class]]) {
            keyboardWindow = testWindow;
            break;
        }
    }
    if (!keyboardWindow) return;

    // Locate UIKeyboard.  
    UIView *foundKeyboard = nil;
    for (UIView __strong *possibleKeyboard in [keyboardWindow subviews]) {

        // iOS 4 sticks the UIKeyboard inside a UIPeripheralHostView.
        if ([[possibleKeyboard description] hasPrefix:@"<UIPeripheralHostView"]) {
            possibleKeyboard = [[possibleKeyboard subviews] objectAtIndex:0];
        }                                                                                

        if ([[possibleKeyboard description] hasPrefix:@"<UIKeyboard"]) {
            foundKeyboard = possibleKeyboard;
            break;
        }
    }

    if (foundKeyboard) {
        [doneButton setImage:[UIImage imageNamed:@"doneupHeb.png"] forState:UIControlStateNormal];
        [doneButton setImage:[UIImage imageNamed:@"donedownHeb.png"] forState:UIControlStateHighlighted];
        doneButton.frame = CGRectMake(-1, 163, 106, 53);
        [foundKeyboard addSubview:doneButton];
        // Add the button to foundKeyboard.
    }

}

-(void)textFieldDidEndEditing:(UITextField *)textField{
    [loan resignFirstResponder];
    [YearCycle resignFirstResponder];
    [prime resignFirstResponder];
    [MothlyReturn resignFirstResponder];   

    [doneButton removeFromSuperview]; 
    doneButton = nil;
}


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

    textField.delegate=self;
    //editingField = textField;

    if ([prime isFirstResponder]||[MothlyReturn isFirstResponder]){

        scroll.contentOffset = CGPointMake(0, 166 );
    }
 //   if ([YearCycle isFirstResponder]){
       // scroll.contentOffset = CGPointMake(0, 200);

}

- (IBAction)closeNumpad:(id)sender{

    [loan resignFirstResponder];
    [YearCycle resignFirstResponder];
    [prime resignFirstResponder];
    [MothlyReturn resignFirstResponder];

    scroll.contentOffset = CGPointMake(0, 0);
    doneButton.hidden=YES;
}

Answer 1

我在网站上其他问题的帮助下解决了这个问题 - 对于所有有或将有问题的人 - 这是代码： 请注意：按钮本身是在xib文件中设计的，而不是在代码中。

.h 文件：

BOOL firstTime;
BOOL add;
BOOL keyboardOpened;
IBOutlet UIButton *doneButton;

.m 文件：

- (void)viewDidLoad
{
    [super viewDidLoad];

    firstTime = TRUE;
    add = TRUE;

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardDidShow:) name:UIKeyboardDidShowNotification object:nil]; // Do any additional setup after loading the view, typically from a nib.
}

- (void)viewDidUnload
{

    //  [[NSNotificationCenter defaultCenter] removeObserver:self];

    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

- (void)addButtonToKeyboard {
    // create custom button
    /* UIButton *doneButton = [UIButton buttonWithType:UIButtonTypeCustom];
     doneButton.frame = CGRectMake(0, 163, 106, 53);
     doneButton.adjustsImageWhenHighlighted = NO;
     [doneButton setImage:[UIImage imageNamed:@"DoneUp.png"] forState:UIControlStateNormal];
     [doneButton setImage:[UIImage imageNamed:@"DoneDown.png"] forState:UIControlStateHighlighted];
     doneButton.tag = 3;
     [doneButton addTarget:self action:@selector(doneButton:) forControlEvents:UIControlEventTouchUpInside];*/
    // locate keyboard view
    UIWindow* tempWindow = [[[UIApplication sharedApplication] windows] objectAtIndex:1];
    UIView* keyboard;
    for(int i=0; i<[tempWindow.subviews count]; i++) {
        keyboard = [tempWindow.subviews objectAtIndex:i];
        // keyboard found, add the button
        if ([[keyboard description] hasPrefix:@"<UIPeripheralHostView"] == YES && add){
            doneButton.frame = CGRectMake(-1, 163, 106, 53);
            [keyboard addSubview:doneButton];

        }    
    }
}

- (void)removeButtonFromKeyboard
{
    // locate keyboard view
    UIWindow* tempWindow = [[[UIApplication sharedApplication] windows] objectAtIndex:1];
    UIView* keyboard;
    for(int i=0; i<[tempWindow.subviews count]; i++) {
        keyboard = [tempWindow.subviews objectAtIndex:i];
        // keyboard found, remove the button
        if([[keyboard description] hasPrefix:@"<UIPeripheralHost"] == YES) [[keyboard viewWithTag:3] removeFromSuperview];
    }
}

- (IBAction)doneButton:(id)sender {
    [loan resignFirstResponder];
    [YearCycle resignFirstResponder];
    [ageOfCeo resignFirstResponder];
    [YearofBusiness resignFirstResponder];
    scroll.contentOffset = CGPointMake(0, 0);

    if (![[[UIDevice currentDevice] model] isEqualToString:@"iPad"] && ![[[UIDevice currentDevice] model] isEqualToString:@"iPad Simulator"])
    {
        [self removeButtonFromKeyboard];
        firstTime = TRUE;
    }
}

- (BOOL)textFieldShouldReturn:(UITextField *)theTextField {
    [theTextField resignFirstResponder];
    return YES;
}

- (void)textFieldDidBeginEditing:(UITextField *)textField
{
    if ([ageOfCeo isFirstResponder]||[YearofBusiness isFirstResponder]){

        scroll.contentOffset = CGPointMake(0, 166 );
    }

    //   firstResponder = textField;
}

- (void)keyboardDidShow:(id)sender
{
    if (![[[UIDevice currentDevice] model] isEqualToString:@"iPad"] && ![[[UIDevice currentDevice] model] isEqualToString:@"iPad Simulator"]) 
    {
        NSLog(@"%@",[[UIDevice currentDevice] model]);
        [self addButtonToKeyboard];
        keyboardOpened = TRUE;
    }
}

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

    if (![[[UIDevice currentDevice] model] isEqualToString:@"iPad"] && ![[[UIDevice currentDevice] model] isEqualToString:@"iPad Simulator"])
    {
        [self removeButtonFromKeyboard];
        keyboardOpened = FALSE;
    }
}

Answer 2

我认为您的问题是因为您正在删除 - (void)keyboardWillShow 中的观察者 .. 尝试将这一行 [[NSNotificationCenter defaultCenter] removeObserver:self]; 放在 -(void)viewDidUnload 中