如何检查c#中是否设置了类属性?
本文关键字：设置 是否 属性 何检查 检查 | 更新日期: 2023-09-27 18:05:45
我目前正在为我的c#类制作BMI计算器。我的应用要求用户输入身高(以英尺和英寸为单位)和体重(以磅为单位)，或者身高(以厘米为单位)和体重(以公斤为单位)。这是一个选项卡控件，它有用于公制模式或公制模式的按钮。
如果单击了imperial选项卡中的"calculate"按钮，我需要确保highightft、hightin和weightLbs文本框已经填写完毕。然后把它们转换成公制单位。如果单击度量选项卡中的计算按钮，我需要确保highightcm和weightKg文本框已填写。
一旦提供了这些，我就将身高和体重转换为BMI。如果我使用if(heightFt == null)，我会得到以下错误:
The result of the expression is always 'false' since a value of type 'double' is never equal to 'null' of type 'double?'
如何解决这个问题?
这是我的mainwindow . example .cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
namespace BMICalculator
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
private BMICalc _BMICalc;
public MainWindow()
{
_BMICalc = new BMICalc();
InitializeComponent();
}
private void calculateImperial_Click(object sender, RoutedEventArgs e)
{
_BMICalc.heightFt = Convert.ToDouble(heightFt.Text);
_BMICalc.heightIn = Convert.ToDouble(heightIn.Text);
_BMICalc.weightLbs = Convert.ToDouble(weightLbs.Text);
_BMICalc.doCalculation("Imperial");
if (_BMICalc.error == null)
{
MessageBox.Show("Your BMI is " + _BMICalc.bmi + " and you are " + _BMICalc.category, "Your BMI");
}
}
}
}
这是BMICalc.cs
using System;
using System.Windows;
using System.ComponentModel;
namespace BMICalculator
{
class BMICalc :INotifyPropertyChanged
{
public double _heightFt { get; set; }
public double _heightIn { get; set; }
public double _heightCm { get; set; }
public double _weightLbs { get; set; }
public double _weightKg { get; set; }
public double _bmi { get; set; }
public string _category { get; set; }
public string _error { get; set; }
public double heightFt
{
get { return heightFt; }
set
{
_heightFt = value;
OnPropertyChanged("heightFt");
}
}
public double heightIn
{
get { return _heightIn; }
set
{
_heightIn = value;
OnPropertyChanged("heightIn");
}
}
public double heightCm
{
get { return _heightCm; }
set
{
_heightCm = value;
OnPropertyChanged("heightCm");
}
}
public double weightLbs
{
get { return _weightLbs; }
set
{
_weightLbs = value;
OnPropertyChanged("weightLbs");
}
}
public double weightKg
{
get { return _weightKg; }
set
{
_weightKg = value;
OnPropertyChanged("weightKg");
}
}
public double bmi
{
get { return _bmi; }
set
{
_bmi = value;
OnPropertyChanged("bmi");
}
}
public string error
{
get { return _error; }
set
{
_error = value;
OnPropertyChanged("error");
}
}
public string category
{
get { return _category; }
set
{
_category = value;
OnPropertyChanged("category");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName){
if(PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
public void doCalculation(string calculationMode){
if(calculationMode == "Imperial"){
if (heightFt == null)
{
this.error = "You must provide a value for your height in feet!";
}
else if (heightIn == null)
{
this.error = "You must provide a value for your height in inches!";
}
else if (weightLbs == null)
{
this.error = "You must provide a value for your weight in pounds!";
}
else
{
heightFt = Convert.ToDouble(heightFt);
heightIn = Convert.ToDouble(heightIn);
weightLbs = Convert.ToDouble(weightLbs);
_weightKg = Convert.ToDouble(_weightLbs * (1 / 2.2));
_heightCm = Convert.ToDouble((_heightFt + (_heightIn / 12) / 0.032808));
}
} else if(calculationMode == "Metric"){
this.bmi = weightKg / Math.Pow((heightCm / 100), 2);
if (this.bmi < 18.5)
{
this.category = "underweight";
}
else if (this.bmi >= 18.5 && this.bmi < 24.9)
{
this.category = "normalweight";
}
else if (this.bmi >= 25 && this.bmi <= 29.9)
{
this.category = "overweight";
}
else if (this.bmi > 30)
{
this.category = "obese";
}
}
}
}
}
}
你可以让你的double属性为空，这样你可以比较null(默认)。
的例子:
public double? heightIn
{
get { return _heightIn; }
set {
_heightIn = value;
OnPropertyChanged("heightIn");
}
}
在这种情况下，请确保更改相应私有变量的类型以匹配
您从未为您的属性设置默认值。由于double不可能是null，因此您可能需要对照0进行检查。以下划线开头的属性应该只是具有默认值的私有变量。还要考虑只在内部使用metric。
class BMICalc :INotifyPropertyChanged
{
private double _heightFt = 0;
private double _heightIn = 0;
private double _heightCm = 0;
private double _weightLbs = 0;
private double _weightKg = 0;
private double _bmi = 0;
private string _category = null;
private string _error = null;
public double heightFt
{
get { return _heightFt; }
set
{
_heightFt = value;
OnPropertyChanged("heightFt");
}
}
public double heightIn
{
get { return _heightIn; }
set
{
_heightIn = value;
OnPropertyChanged("heightIn");
}
}
public double heightCm
{
get { return _heightCm; }
set
{
_heightCm = value;
OnPropertyChanged("heightCm");
}
}
public double weightLbs
{
get { return _weightLbs; }
set
{
_weightLbs = value;
OnPropertyChanged("weightLbs");
}
}
public double weightKg
{
get { return _weightKg; }
set
{
_weightKg = value;
OnPropertyChanged("weightKg");
}
}
public double bmi
{
get { return _bmi; }
set
{
_bmi = value;
OnPropertyChanged("bmi");
}
}
public string error
{
get { return _error; }
set
{
_error = value;
OnPropertyChanged("error");
}
}
public string category
{
get { return _category; }
set
{
_category = value;
OnPropertyChanged("category");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName){
if(PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
public void doCalculation(string calculationMode){
if(calculationMode == "Imperial"){
if (heightFt == null)
{
this.error = "You must provide a value for your height in feet!";
}
else if (heightIn == null)
{
this.error = "You must provide a value for your height in inches!";
}
else if (weightLbs == null)
{
this.error = "You must provide a value for your weight in pounds!";
}
else
{
heightFt = Convert.ToDouble(heightFt);
heightIn = Convert.ToDouble(heightIn);
weightLbs = Convert.ToDouble(weightLbs);
_weightKg = Convert.ToDouble(_weightLbs * (1 / 2.2));
_heightCm = Convert.ToDouble((_heightFt + (_heightIn / 12) / 0.032808));
}
} else if(calculationMode == "Metric"){
this.bmi = weightKg / Math.Pow((heightCm / 100), 2);
if (this.bmi < 18.5)
{
this.category = "underweight";
}
else if (this.bmi >= 18.5 && this.bmi < 24.9)
{
this.category = "normalweight";
}
else if (this.bmi >= 25 && this.bmi <= 29.9)
{
this.category = "overweight";
}
else if (this.bmi > 30)
{
this.category = "obese";
}
}
}
}
}