在UIPickerViewDelegate方法的末尾显示警告消息

Question

我已经在我的应用程序中创建了一个选择器视图，并为它在我的.h文件中创建了两个组件，代码如下

@interface tweetViewController : UIViewController<UIPickerViewDataSource ,UIPickerViewDelegate> {

    NSArray *activities;
    NSArray *feelings;

}
@property(nonatomic,retain) NSArray *activities;
@property(nonatomic,retain) NSArray *feelings;
@end

之后，在我的.m文件中，我为UIPickerViewDataSource和UIPickerViewDelegate实现了强制方法，但是UIPickerViewDatasource的两个强制方法都工作得很好，并且它的代码是

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
        return [activities count];
    }
    else
    {
        return [feelings count];
    }
} return 2;
}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{
    if (component==0) {
   return [activities count];
    }
    else
    {
        return [feelings count];
    }
}

但是UIPickerViewDelegate的方法在方法的末尾显示了警告

- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
    switch (component) {
        case 0:
            return [activities objectAtIndex:row];
            break;
        case 1:
            return [feelings objectAtIndex:row];
            break;
    }

}

告诉我为什么会出现警告？

Answer 1

警告“控制可能到达非空函数的末尾”意思是说方法没有返回任何东西，因为该方法有一些返回值。

    - (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
    {
        NSString *strToReturn = @"";
        switch (component) {
            case 0:
                strToReturn = [activities objectAtIndex:row];
                break;
            case 1:
                strToReturn = [feelings objectAtIndex:row];
            break;
        }
        return strToReturn;
    }

如上所述修改您的代码，警告将不会再激怒您。

Answer 2

//numberOfRowsInComponent must return NSInteger value

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{
    if (component==0) {
        return [activities count];//then wont execute feelings count
    }//if loop failed then ur feeling count

    return [feelings count];
}

//here u can remove else loop with same meaning with your context 

对于titleForRow方法，至少在默认情况下必须返回nsstring

因此为某些字符串指定默认大小写