为什么resignFirstResponder在iOS 5.0中被调用两次，而在iOS4.2-4.3中只被调用一次？

Question

我在 App Store 中有一个为 4.2 编译的应用程序，在 iOS 5.0 下运行时表现得很奇怪。我已经追踪到 resignFirstResponder 在 iOS 5.0 下被调用了两次，而在 iOS 4.2 和 4.0 下只被调用了一次。 4.3.

我从 UITextField 派生了一个类，我在其中重写了 resignFirstResponder。请参阅下面的示例代码。

在 iOS 4.2 & 下4.3 我在控制台中看到以下内容：

textFieldShouldReturn
resignFirstResponder
textFieldDidEndEditing

在 iOS 5.0 下，我在控制台中看到以下内容：

textFieldShouldReturn
resignFirstResponder
resignFirstResponder
textFieldDidEndEditing

在设备和模拟器上运行代码给出了恒定的结果。我错过了什么还是这是一个错误？

iOS 5.0 堆栈跟踪

#0  -[BugTextField resignFirstResponder] (self=0x681b530, _cmd=0x3769b41) at /Users/.../BugTextField.m:14
#1  0x006c05a6 in -[UIFieldEditor resignFirstResponder] ()
#2  0x006374e3 in -[UIView(Hierarchy) _willMoveToWindow:] ()
#3  0x006362c2 in __UIViewWillBeRemovedFromSuperview ()
#4  0x006360d7 in -[UIView(Hierarchy) removeFromSuperview] ()
#5  0x006bfff7 in -[UIFieldEditor becomeFieldEditorForView:] ()
#6  0x006ae37b in -[UITextField _resignFirstResponder] ()
#7  0x006eb8d4 in -[UIResponder _finishResignFirstResponder] ()
#8  0x006eba20 in -[UIResponder resignFirstResponder] ()
#9  0x006ae249 in -[UITextField resignFirstResponder] ()
#10 0x00017f68 in -[BugTextField resignFirstResponder] (self=0x681b530, _cmd=0x3769b41) at /Users/.../BugTextField.m:16
#11 0x0001828f in -[BugTextFieldVC textFieldShouldReturn:] (self=0x6829750, _cmd=0x18c5b, textField=0x681b530) at /Users/.../BugTextFieldVC.m:40

BugTextField.h

#import <UIKit/UIKit.h>

@interface BugTextField : UITextField

@end

BugTextField.m

#import "BugTextField.h"

@implementation BugTextField

- (BOOL) resignFirstResponder
{
    NSLog(@"resignFirstResponder");

    return [super resignFirstResponder];
}

@end

BugTextFieldVC.h

#import <UIKit/UIKit.h>
@class BugTextField;

@interface BugTextFieldVC : UIViewController <UITextFieldDelegate> {
    BugTextField *bugTextField;
}

@end

BugTextFieldVC.m

#import "BugTextFieldVC.h"
#import "BugTextField.h"

@implementation BugTextFieldVC

- (id) init
{
    if ( !(self = [super init]) )
    {
        return self;
    }

    // One text field with 100 height keyboard
    bugTextField = [[BugTextField alloc] initWithFrame:CGRectMake(10, 10, 300, 30)];
    bugTextField.borderStyle = UITextBorderStyleRoundedRect;
    bugTextField.delegate = self;
    [self.view addSubview:bugTextField];

    return self;
}

- (void) dealloc
{
    [bugTextField release];

    [super dealloc];
}

- (BOOL) textFieldShouldReturn:(UITextField *)textField
{
    NSLog(@"textFieldShouldReturn");

    [textField resignFirstResponder];

    return YES;
}

- (void) textFieldDidEndEditing:(UITextField *)textField
{
    NSLog(@"textFieldDidEndEditing");
}

@end

Answer 1

下面是适用于 iOS 4.2、4.3 和 5.0 的解决方法，它既不是火箭科学，也不是性感的，但它会起作用，直到我更好地理解正在发生的事情（我做错了什么还是这是一个错误？） 。我将此作为错误报告给 Apple。

BugTextField.h

#import <UIKit/UIKit.h>

@interface BugTextField : UITextField {
    // Value used to ensure code in resignFirstResponder is executed by the 
    // first stack frame and not subsequent stack frames in iOS 5.0.
    //
    // In iOS 5.0, one call to resignFirstResponder results in a second call to
    // resignFirstResponder.  In iOS 4.2 & 4.3, one call to resignFirstResponder
    // does not result in subsequent calls to resignFirstResponder.
    NSUInteger resignFirstResponderCallDepth;
}

@end

BugTextField.m

#import "BugTextField.h"

@implementation BugTextField

- (BOOL) resignFirstResponder
{
    if (0 == resignFirstResponderCallDepth++)
    {
        // ---------------------------------------------------------------------
        // Code executed by first stack frame to call resignFirstResponder.
        NSLog(@"resignFirstResponder");
    }

    // -------------------------------------------------------------------------
    // Code executed by every stack frame to call resignFirstResponder.
    BOOL rV = [super resignFirstResponder];

    resignFirstResponderCallDepth--;

    return rV;
}

@end

Answer 2

一种解决方案是重写 canResignFirstResponder 。这只会被调用一次。

问题是这与文档不一致 - https://developer.apple.com/library/ios/#DOCUMENTATION/UIKit/Reference/UIResponder_Class/Reference/Reference.html - 所以你可能是对的：这是一个错误。