Question

C＃UWP应用XAML（身体质量指数计算器 - BMI）

我需要TextBox txtKG.Text并将其传递给txtDescription.Text

我假设我必须以某种方式创建TextBox类的实例，但我坚持这个错误2天。我尝试了很多方法，但我不知道该怎么做。

错误消息：

System.NullReferenceException：“对象引用未设置为对象的实例。”

MY XAML细分：

<Slider x:Name="sldKG" HorizontalAlignment="Left" Margin="170,306,0,0" VerticalAlignment="Top" Width="184" ValueChanged="Slider_ValueChanged" Minimum="40" Maximum="150" Value="70"/>

<TextBox x:Name="txtKG" FontSize="18" HorizontalAlignment="Left" Margin="50,310,0,0" VerticalAlignment="Top" TextAlignment="Center" Text="{Binding ElementName=sldKG,Path=Value}"/>

<TextBlock FontSize="18" x:Name="kg" HorizontalAlignment="Left" Margin="121,316,0,0" Text="kg" TextWrapping="Wrap" VerticalAlignment="Top"/>
<Slider x:Name="sldCM" HorizontalAlignment="Left" Margin="170,366,0,0" VerticalAlignment="Top" Width="184" ValueChanged="Slider_ValueChanged" Minimum="145" Maximum="240" Value="170"/>

<TextBlock FontSize="18" x:Name="txtDescription" HorizontalAlignment="Left" Margin="52,499,0,0" Text="Type Your parameters and i wil show Your BMI" TextWrapping="Wrap" VerticalAlignment="Top" Height="96" Width="302" TextAlignment="Center"/>

MyPage.xaml.cs

namespace Kalkulator_BMI_UWP
{   
    public sealed partial class MainPage : Page  
    {            
        public MainPage()
        {
            this.InitializeComponent();
}

private void Slider_ValueChanged(object sender, RangeBaseValueChangedEventArgs e)
{
txtDescription.Text = txtKG.Text;   // <!-- HERE IS THIS ERROR
       }

Answer 1

问题在于Slider值更改事件，因为尚未加载控件（XAML中的TextBlocks）而发生错误，作为一种解决方法（我在一些项目中执行），您可以使用try-catch语句封装该方法，如下所示：

library('shiny')

ui<-fluidPage(
  titlePanel("Sample Size Calculation"),

  numericInput("num1", 
               h3("Power to be reached"), 
               value = 0.85, min=0, max=1,step=0.01),

  numericInput("num2", 
               h3("Scale parameter"),value=25,step=0.1),

  numericInput("num3", 
               h3("delta"), 
               value = 2,step=0.01),

  numericInput("num4", 
               h3("allocation ratio"), 
               value = 1,min=0, step=0.01),


  numericInput("num5", 
               h3("Beta"), 
               value = 0.1062, min=0, step=0.01),

  numericInput("num6", 
               h3("event probability"), 
               value = 1,min=0, max=1,step=0.01),

  numericInput("num7", 
               h3("Significant level"), 
               value = 0.05, min=0, max=1,step=0.01),

  plotOutput("picture"),
  textOutput("k_gamma"),
  submitButton("Submit")

)

server<-function(input,output){
  n=2
  power1=rep(NA,2*n)
  ndf=rep(NA,2*n)
  ddf=rep(NA,2*n)
  f_crit1=rep(NA,2*n)
  f_crit2=rep(NA,2*n)
  criticalvalue1=rep(NA,2*n)
  criticalvalue2=rep(NA,2*n)
  x=rep(NA,2*n)

  my_func<-reactive({
    k_gamma<-input$num2
    delta_pt<-input$num3
    r<-input$num4
    beta<-input$num5
    eventprob<-input$num4
    alpha<-input$num7


    for (i in 1:(2*n)) {

      ndf[i]=2*ceiling(eventprob*i)*k_gamma
      ddf[i]=2*ceiling(eventprob*i)*r*k_gamma
      f_crit1[i]= qf(1-alpha,ndf[i],ddf[i])
      f_crit2[i] = qf(alpha,ndf[i],ddf[i])
      criticalvalue1[i]=(f_crit1[i]*r)/((delta_pt**(beta)))
      criticalvalue2[i]=(f_crit2[i]*r)/((delta_pt**(beta)))
      power1[i]=1-pf(criticalvalue1[i],ndf[i],ddf[i])+pf(criticalvalue2[i],ndf[i],ddf[i])
      samplesize1=c(ceiling(n/2):(2*n))
      powervector1=power1[ceiling(n/2):(2*n)]

    }

  })

  output$picture<-renderPlot({plot(my_func()$samplesize1, my_func()$powervector1 ,xlim=c(0,200),ylim=c(0,1))})
}

shinyApp(ui, server)

将TextBox文本分配给TextBlock - System.NullReferenceException：“未设置对象引用...”

1 个答案: