Command Binding with Parameter Passing

We saw the example of command binding to calculate the GCD and LCM of two input numbers. Now lets extend this idea and trying to pass some parameter while doing command binding. We have the same signature of calculating LCM and GCD so we are passing one parameter during the command binding to decide which function to call. Let’s take a look at our numbers class now. It is very simple and the difference is now we are making only one property of ICommand rather than two because we are binding only one method. And that method internally calls two different methods depends on parameter. This is again ground work for MVVM.

Here is our Number class.

  1: public class Numbers

  2: {

  3:     public int FirstNo

  4:     { get; set; }

  5: 

  6:     public int SecondNo

  7:     { get; set; }

  8: 

  9:     public ICommand CalculateCommand

 10:     { get; set; }

 11: }

 12: 
Now we implement the ICommand nterface but this time our function take String as a parameter. Here is our command class. 
  1: public class MyCommand : ICommand

  2: {

  3:     public Func<String, int> Function

  4:     { get; set; }

  5: 

  6:     public bool CanExecute(object parameter)

  7:     {

  8:         if (Function != null)

  9:         {

 10:             return true;

 11:         }

 12: 

 13:         return false;

 14:     }

 15: 

 16: 

 17:     public void Execute(object parameter)

 18:     {

 19:         if (Function != null)

 20:         {

 21:             String str = parameter as String;

 22: 

 23:             Function(str);

 24:         }

 25:     }

 26: 

 27:     public event EventHandler CanExecuteChanged

 28:     {

 29:         add { CommandManager.RequerySuggested += value; }

 30:         remove { CommandManager.RequerySuggested -= value; }

 31:     }

 32: }

 33: 
Here is our XAML file to pass parameter in the binding method. 
  1: <Button Grid.Column="0" Grid.Row="2" Margin="5" 

  2: 	Content="GCD" Command="{Binding CalculateCommand}" CommandParameter="GCD"/>

  3: <Button Grid.Column="1" Grid.Row="2" Margin="5" 

  4: 	Content="LCM" Command="{Binding CalculateCommand}" CommandParameter="LCM"/>        

  5: 
Now “GCD” will pass as a parameter when first button click and “LCM” will pass when second button clicks. Here is our binding method that calls two different methods depends on its parameter. 
  1: private int Command(String parameter)

  2: {

  3:     int x = nos.FirstNo;

  4:     int y = nos.SecondNo;

  5: 

  6:     if (parameter == "GCD")

  7:     {

  8:         int gcd =  CalculateGCD(x, y);

  9:         MessageBox.Show(gcd.ToString(), "GCD");

 10:         return gcd;

 11:     }

 12:     else if (parameter == "LCM")

 13:     {

 14:         int lcm = CalculateLCM(x, y);

 15:         MessageBox.Show(lcm.ToString(), "LCM");

 16:         return lcm;

 17:     }

 18:     else

 19:         return 0;

 20: }

 21: 
Here is complete XAML code of the program.
  1: <Window x:Class="WpfCommandBinding.Window1"

  2:     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

  3:     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

  4:     Title="Command Binding" Height="200" Width="300">

  5:     <Grid Name="grid" Background="Wheat">

  6:         <Grid.ColumnDefinitions>

  7:             <ColumnDefinition/>

  8:             <ColumnDefinition/>

  9:         </Grid.ColumnDefinitions>

 10:         <Grid.RowDefinitions>

 11:             <RowDefinition/>

 12:             <RowDefinition/>

 13:             <RowDefinition/>

 14:         </Grid.RowDefinitions>

 15:         <TextBlock Grid.Column="0" Grid.Row="0" Margin="5"

 16:                    VerticalAlignment="Center" Text="Enter first number"/>

 17:         <TextBox Grid.Column="1" Grid.Row="0" Margin="5" Name="txtFirstNo"

 18:                  VerticalAlignment="Center" Text="{Binding Path=FirstNo}"/>

 19:         <TextBlock Grid.Column="0" Grid.Row="1" Margin="5"

 20:                    VerticalAlignment="Center" Text="Enter second number"/>

 21:         <TextBox Grid.Column="1" Grid.Row="1" Margin="5" Name="txtSecondNo"

 22:                    VerticalAlignment="Center" Text="{Binding Path=SecondNo}"/>

 23:         <Button Grid.Column="0" Grid.Row="2" Margin="5" 

 24:                 Content="GCD" Command="{Binding CalculateCommand}" CommandParameter="GCD"/>

 25:         <Button Grid.Column="1" Grid.Row="2" Margin="5" 

 26:                 Content="LCM" Command="{Binding CalculateCommand}" CommandParameter="LCM"/>        

 27:     </Grid>

 28: </Window>

 29: 
And here is complete C# code of the program.
  1: using System;

  2: using System.Collections.Generic;

  3: using System.Linq;

  4: using System.Text;

  5: using System.Windows;

  6: using System.Windows.Controls;

  7: using System.Windows.Data;

  8: using System.Windows.Documents;

  9: using System.Windows.Input;

 10: using System.Windows.Media;

 11: using System.Windows.Media.Imaging;

 12: using System.Windows.Navigation;

 13: using System.Windows.Shapes;

 14: using System.ComponentModel;

 15: 

 16: namespace WpfCommandBinding

 17: {

 18:     /// <summary>

 19:     /// Interaction logic for Window1.xaml

 20:     /// </summary>

 21:     public partial class Window1 : Window

 22:     {

 23:         private Numbers nos = new Numbers();

 24: 

 25:         public Window1()

 26:         {

 27:             InitializeComponent();

 28:             MyCommand command = new MyCommand();

 29:             command.Function = Command;

 30:             nos.CalculateCommand = command;

 31: 

 32:             grid.DataContext = nos;

 33:         }

 34: 

 35:         private int Command(String parameter)

 36:         {

 37:             int x = nos.FirstNo;

 38:             int y = nos.SecondNo;

 39: 

 40:             if (parameter == "GCD")

 41:             {

 42:                 int gcd =  CalculateGCD(x, y);

 43:                 MessageBox.Show(gcd.ToString(), "GCD");

 44:                 return gcd;

 45:             }

 46:             else if (parameter == "LCM")

 47:             {

 48:                 int lcm = CalculateLCM(x, y);

 49:                 MessageBox.Show(lcm.ToString(), "LCM");

 50:                 return lcm;

 51:             }

 52:             else

 53:                 return 0;

 54:         }

 55: 

 56:         private int CalculateGCD(int x, int y)

 57:         {

 58:             if (x == 0)

 59:                 return 0;

 60: 

 61:             while (y != 0)

 62:             {

 63:                 if (x > y)

 64:                     x = x - y;

 65:                 else

 66:                     y = y - x;

 67:             }

 68: 

 69:             return x;

 70:         }

 71: 

 72:         private int CalculateLCM(int x, int y)

 73:         {

 74:             int lcm = x * y / CalculateGCD(x, y);

 75:             return x * y / lcm;

 76:         }

 77:     }

 78: 

 79:     public class MyCommand : ICommand

 80:     {

 81:         public Func<String, int> Function

 82:         { get; set; }

 83: 

 84:         public bool CanExecute(object parameter)

 85:         {

 86:             if (Function != null)

 87:             {

 88:                 return true;

 89:             }

 90: 

 91:             return false;

 92:         }

 93: 

 94: 

 95:         public void Execute(object parameter)

 96:         {

 97:             if (Function != null)

 98:             {

 99:                 String str = parameter as String;

100: 

101:                 Function(str);

102:             }

103:         }

104: 

105:         public event EventHandler CanExecuteChanged

106:         {

107:             add { CommandManager.RequerySuggested += value; }

108:             remove { CommandManager.RequerySuggested -= value; }

109:         }

110:     }

111: 

112:     public class Numbers

113:     {

114:         public int FirstNo

115:         { get; set; }

116: 

117:         public int SecondNo

118:         { get; set; }

119: 

120:         public ICommand CalculateCommand

121:         { get; set; }

122:     }

123: }

124: 
The output of this program is same as previous one. Here is the output of this program. 



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