如何检查是否在C＃中设置了类属性？

时间：2015-08-01 00:28:27

标签： c#

我目前正在为我的C＃类开发BMI计算器。我的应用程序要求用户以英尺和英寸为单位的高度和以磅为单位的重量或以厘米为单位的高度以及以千克为单位的重量。它们是一个标签控件，具有用于英制模式或公制模式的按钮。

如果＆＃34;计算＆＃34;单击英制标签中的按钮，我需要确保已填写heightFt，heightIn和weightLbs文本框。然后我将它们转换为公制单位。如果单击度量标签中的计算按钮，我需要确保已填写heightCm和weightKg文本框。

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)，我会收到以下错误：

The result of the expression is always 'false' since a value of type 'double' is never equal to 'null' of type 'double?'

我该如何解决这个问题？

这是我的MainWindow.xaml.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";
                    }

                }

            }
        }
    }
}

2 个答案:

答案 0 :(得分：2)

您可以使double属性可以为空，这样您就可以比较为null（默认值）。

示例：

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。

答案 1 :(得分：0)

您永远不会为您的媒体资源设置默认值。由于double不能null，您可能希望检查0而不是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"; } } } } } 。以下划线开头的属性应该只是具有默认值的私有变量。另请考虑仅在内部使用指标。

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