objective-c - 一元表达式的参数类型“NSString”无效

Question

即使我从 Apple 文档中复制了该方法，我也遇到了返回错误（已注释掉）的问题。

你能告诉我有什么问题吗？

提前致谢。

#import "BIDDependentComponentViewController.h"


@implementation BIDDependentComponentViewController

- (IBAction)buttonPressed
{
    NSInteger stateRow = [self.dependentPicker selectedRowInComponent:kStateComponent];
    NSInteger zipRow = [self.dependentPicker selectedRowInComponent:kZipComponent];

    NSString *state = self.states[stateRow];
    NSString *zip = self.zips[zipRow];

    NSString *title = [[NSString alloc] initWithFormat:@"You selected zip code %@", zip];
    NSString *message = [[NSString alloc] initWithFormat:@"%@ is in %@", zip, state];

    UIAlertView *alert = [[UIAlertView alloc]initWithTitle:title
                                                   message:message
                                                  delegate:nil
                                         cancelButtonTitle:@"OK"
                                         otherButtonTitles:nil];
    [alert show];   
}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
    NSBundle *bundle = [NSBundle mainBundle];
    NSURL *plistURL = [bundle URLForResource:@"statedictionary" withExtension:@"plist"];

    self.stateZips = [NSDictionary dictionaryWithContentsOfURL:plistURL];
    NSArray *allStates = [self.stateZips allKeys];
    NSArray *sortedStates = [allStates sortedArrayUsingSelector:@selector(compare:)];
    self.states = sortedStates;

    NSString *selectedState = self.states[0];
    self.zips = self.stateZips[selectedState];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark-
#pragma mark Picker Data Source Methods

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
    return 2;
}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{
    if(component == kStateComponent)
    {
        return[self.states count];
    } else {
        return[self.zips count];
    }
}

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
{
    if(component == kStateComponent)
    {
        NSString *selectedState = self.states[row];
        self.zips = self.stateZips[selectedState];
        [self.dependentPicker reloadComponent:kZipComponent];
        [self.dependentPicker selectRow:0 inComponent:kZipComponent animated:YES];
    }



#pragma mark Picker Delegate Methods

-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component //Invalid argument type 'NSString' to unary expression
{
    if(component == kStateComponent)
    {
        return self.states[row];
    } else {
        return self.states[row];
    }
}

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
{
    if(component == kStateComponent)
    {NSString *selectedState = self.states[row];
    self.zips = self.stateZips[selectedState];
    [self dependentPicker selectRow:0
    inComponent:kZipComponent
    animated:YES];
}

@end // Missing @end

Answer 1

您缺少}此方法的右括号：

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component

将支架放在正确的位置（就在上面#pragma mark Picker Delegate Methods ）将解决您的两个错误。