如何让 UIPickerview 自动更新 UILabel

Question

我有一个转换器应用程序，我希望它在我将数字（应该转换的）输入到文本字段时更新标签。我希望它自动更新，所以我不需要再次选择轮子上的单元来更新它。

这是我的代码：

- (void)viewDidLoad
{
   [super viewDidLoad];
  {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    _convertFrom = @[@"MTPA", @"MMcf/day",
    @"Mill.Sm3/day", @"MMBTU", @"Boe/day"];

    _convertRates = @[ @1.0f, @133.4246575f, @3.780821918f,
    @142465.7534f, @23780.8f];

    _convertTo = @[@"MTPA", @"MMcf/day",
    @"Mill.Sm3/day", @"MMBTU", @"Boe/day"];

    _convertRates = @[ @1.0f, @133.4246575f, @3.780821918f,
    @142465.7534f, @23780.8f];
}
}

我应该在这里做什么？

- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];

}

-(IBAction)textFieldReturn:(id)sender
{
    [sender resignFirstResponder];
}
-(IBAction)backgroundTouched:(id)sender
{
    [inputText resignFirstResponder];
}


#pragma mark -
#pragma mark PickerView DataSource

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

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


 - (NSString *) pickerView: (UIPickerView *)pickerView
          titleForRow:(NSInteger)row
         forComponent:(NSInteger)component
{
if (component == 0) {
    return [_convertFrom objectAtIndex:row];
}
return [_convertTo objectAtIndex:row];
}




 #pragma mark -
 #pragma mark PickerView Delegate
 -(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row
   inComponent:(NSInteger)component

 {
 float convertFrom = [[_convertRates objectAtIndex:[pickerView selectedRowInComponent:0]]     floatValue];
 float convertTo = [[_convertRates objectAtIndex:[pickerView selectedRowInComponent:1]] floatValue];

float input = [inputText.text floatValue];
float to = convertTo;
float from = convertFrom;
float convertValue = input;
float relative = to / from;
float result = relative * convertValue;
NSString *convertFromName = [_convertFrom objectAtIndex:[pickerView selectedRowInComponent:0]];
NSString *convertToName = [_convertFrom objectAtIndex:[pickerView selectedRowInComponent:1]];


NSString *resultString = [[NSString alloc]initWithFormat:
                          @" %.4f %@ = %.4f %@",convertValue, convertFromName, result, convertToName];
resultLabel.text = resultString; 



}

Answer 1

您的问题与选择器视图无关。您想监听文本字段的更改并根据输入文本字段的最新文本更新转换和标签。

1. 设置在文本字段值更改时调用的方法。
2. 选择器视图委托方法中计算转换和更新标签的所有代码都需要放在另一个可以从两个位置调用的方法中。
3. 在对文本字段中的更改做出反应的新方法中，调用您刚刚创建的方法来执行转换并更新标签。

所以此时您的选择器视图委托方法和您的文本字段更改方法都调用从选择器获取转换的方法和从文本字段中获取文本，然后进行转换，最后更新标签。

编辑：更多细节

像这样重构当前的选择器视图委托方法：

-(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component {
    [self updateConversionLabel];
}

- (void)updateConversionLabel {
    float convertFrom = [[_convertRates objectAtIndex:[pickerView selectedRowInComponent:0]] floatValue];
    float convertTo = [[_convertRates objectAtIndex:[pickerView selectedRowInComponent:1]] floatValue];

    float input = [inputText.text floatValue];
    float to = convertTo;
    float from = convertFrom;
    float convertValue = input;
    float relative = to / from;
    float result = relative * convertValue;
    NSString *convertFromName = [_convertFrom objectAtIndex:[pickerView selectedRowInComponent:0]];
    NSString *convertToName = [_convertFrom objectAtIndex:[pickerView selectedRowInComponent:1]];

    NSString *resultString = [[NSString alloc]initWithFormat:
        @" %.4f %@ = %.4f %@",convertValue, convertFromName, result, convertToName];
    resultLabel.text = resultString; 
}

然后您需要创建一个方法来处理对文本字段的更改：

- (void)textFieldChanged:(UITextField *)textField {
    [self updateConversionLabel];
}

现在在 IB 中，将 textFieldChanged: 方法连接到 inputText 文本字段的“值更改”事件。我不使用 IB，所以我不知道这样做的确切术语。