在Xcode 4.5.2& ;;下编译时，UIPickerView无法自动选择最后一行。 iOS 6 [英] UIPickerView can't autoselect last row when compiled under Xcode 4.5.2 & iOS 6
问题描述
我一直在试图诊断我的应用无法使用在旧版XCode下成功运行的代码自动预选UIPickerView的最后一行。我认为这是Xcode而不是iOS 6中的一个错误，因为我在iOS 6设备上运行的旧应用程序运行正常，但重新编译Xcode 4.5.2下的代码行为不正常。我已经整理了以下示例来演示问题，但在我提交错误报告之前，我希望此论坛上的其他人能够确定问题是否与我的代码有关，或者确实是Xcode / iOS中的错误。
我创建了一个单一的视图应用程序，并使用导航控制器和两个IBOutlet设置故事板，一个到UILabel，我在那里显示所选行，一个到UIPickerView。 / p>
以下是我的自定义视图控制器的头文件：
＃ import< UIKit / UIKit.h>
@interface DisposableViewController：UIViewController
< UIPickerViewDataSource，UIPickerViewDelegate>
@end
这是我的自定义视图控制器的实现文件：
#importDisposableViewController.h
const NSInteger MAX_VALUE = 10;
@interface DisposableViewController（）
@property（弱，非原子）IBOutlet UIPickerView * pickerView;
@property（弱，非原子）IBOutlet UILabel * selectedValueLabel;
@end
@implementation DisposableViewController
- （void）viewDidLoad
{
[super viewDidLoad ]。
}
- （void）viewWillAppear：（BOOL）动画
{
[self.pickerView reloadAllComponents];
[self.pickerView selectRow：MAX_VALUE inComponent：0 animated：NO];
self.selectedValueLabel.text = [NSString stringWithFormat：@％d，[self.pickerView selectedRowInComponent：0]];
}
// **
// ** UIPickerViewDataSource方法
// **
- （NSInteger ）numberOfComponentsInPickerView：（UIPickerView *）pickerView
{
return 1;
}
- （NSInteger）pickerView：（UIPickerView *）pickerView numberOfRowsInComponent：（NSInteger）组件
{
返回MAX_VALUE + 1;
}
// **
// ** UIPickerViewDelegate方法
// **
- （NSString *）pickerView：（UIPickerView *）pickerView titleForRow：（NSInteger）row forComponent：（NSInteger）component
{
return [NSString stringWithFormat：@％d，row];
}
- （void）pickerView：（UIPickerView *）pickerView didSelectRow：（NSInteger）row inComponent：（NSInteger）component
{
self .selectedValueLabel.text = [NSString stringWithFormat：@％d，row];
}
@end
这是显示问题的屏幕截图：
请注意，我的代码尝试在viewWillAppear：方法中自动选择UIPickerView中的最后一行，但是当程序运行时，值标签在调用[self]时将行作为10 .pickerView selectedRowInComponent：0]，但是UIPickerView本身在视觉上看起来已经选择了9.我相信这是一个错误，但是想要我如何解决这个问题的其他意见或建议。感谢您的关注。
此错误是由故事板中的Use Autolayout选项引起的，但我找到了一个解决方法允许我继续使用自动布局：
如果我在视图控制器的viewDidAppear中调用[pickerView selectRow：inComponent：]方法而不是在viewWillAppear：中，然后UIPickerView正确调整以选择正确的行，尽管当选择器从错误的选择旋转到正确的选择时，选择暂时可见。
I have been beating my head against the wall trying to diagnose my app's inability to automatically preselect the last row of a UIPickerView using code that successfully worked under older versions of XCode. I think this is a bug in Xcode rather than iOS 6 because my old app running on an iOS 6 device works properly, but recompiling the code under Xcode 4.5.2 does not behave properly. I have put together the following sample to demonstrate the problem, but before I submit a bug report, I would like opinions from others on this forum to determine if the problem is with my code or is indeed a bug in Xcode/iOS.
I created a single view app and setup the storyboard with a navigation controller, and two IBOutlets, one to a UILabel where I display the selected row, and one to a UIPickerView.
Here is the header file for my custom view controller:
#import <UIKit/UIKit.h>
@interface DisposableViewController : UIViewController
<UIPickerViewDataSource, UIPickerViewDelegate>
@end
Here is the implementation file for my custom view controller:
#import "DisposableViewController.h"
const NSInteger MAX_VALUE = 10;
@interface DisposableViewController ()
@property (weak, nonatomic) IBOutlet UIPickerView *pickerView;
@property (weak, nonatomic) IBOutlet UILabel *selectedValueLabel;
@end
@implementation DisposableViewController
- (void)viewDidLoad
{
[super viewDidLoad];
}
- (void)viewWillAppear:(BOOL)animated
{
[self.pickerView reloadAllComponents];
[self.pickerView selectRow:MAX_VALUE inComponent:0 animated:NO];
self.selectedValueLabel.text = [NSString stringWithFormat:@"%d", [self.pickerView selectedRowInComponent:0]];
}
//**
//** UIPickerViewDataSource methods
//**
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
return 1;
}
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{
return MAX_VALUE + 1;
}
//**
//** UIPickerViewDelegate methods
//**
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
return [NSString stringWithFormat:@"%d", row];
}
- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
{
self.selectedValueLabel.text = [NSString stringWithFormat:@"%d", row];
}
@end
Here is a screenshot demonstrating the problem:
Note that my code tries to autoselect the last row in the UIPickerView in the viewWillAppear: method, but when the program runs, the value label gets the row as 10 when calling [self.pickerView selectedRowInComponent:0], but the UIPickerView itself visually appears to have selected 9. I believe this is a bug, but would like other opinions or suggestions for how I can resolve this problem. Thanks for your attention.
This bug is caused by the Use Autolayout option in the storyboard, but I have found a workaround that allows me to continue using auto layout:
If I call the [pickerView selectRow:inComponent:] method in the viewDidAppear: of my view controller instead of in the viewWillAppear:, then the UIPickerView correctly adjusts to select the correct row though the selection is momentarily visible as the picker rotates from the wrong selection to the correct one.
这篇关于在Xcode 4.5.2& ;;下编译时，UIPickerView无法自动选择最后一行。 iOS 6的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
