[英]Why Mvvm approach is not working for my Calculator?
我正在尝试使用silverlight 5在MVVM上工作,而我的xaml代码是这样的:
<Grid x:Name="LayoutRoot" Background="White" Height="100" Width="350">
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition/>
<ColumnDefinition/>
<ColumnDefinition/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition/>
</Grid.RowDefinitions>
<TextBox Grid.Column="0" Text="{Binding FirstValue, Mode=TwoWay}" Height="25" TextAlignment="Right"/>
<TextBlock Grid.Column="1" Text="+" Height="25" TextAlignment="Center"/>
<TextBox Grid.Column="2" Text="{Binding SecondValue, Mode=TwoWay}" Height="25" TextAlignment="Right"/>
<TextBlock Grid.Column="3" Text="=" Height="25" TextAlignment="Center"/>
<TextBlock Grid.Column="4" Text="{Binding Result, Mode=OneWay}" Height="25" TextAlignment="Left"/>
<Button Grid.Row="1" Grid.ColumnSpan="5" Margin="0,5,0,0" Content="Calculate" Command="{Binding CalculateCommand}" />
</Grid>
和
public MainPage()
{
InitializeComponent();
this.DataContext = new CalculatorViewModel();
}
我的CalculatorViewModel.cs类是:
public class CalculatorViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public CalculatorModel cc;
private string _firstValue;
public string FirstValue
{
get { return _firstValue; }
set
{
_firstValue = value;
OnPropertyChanged("FirstValue");
}
}
private string _secondValue;
public string SecondValue
{
get { return _secondValue; }
set
{
_secondValue = value;
OnPropertyChanged("SecondValue");
}
}
private string _result;
public string Result
{
get { return _result; }
private set
{
_result = value;
OnPropertyChanged("Result");
}
}
private ICommand _calculateCommand;
public ICommand CalculateCommand
{
get { return _calculateCommand; }
}
public CalculatorViewModel()
{
cc = new CalculatorModel();
cc.FirstValue = _firstValue;
cc.SecondValue = _secondValue;
cc.Result = _result;
_calculateCommand = new RelayCommand(cc.Calculate) { IsEnabled = true };
//This Calculate() is defined in Model class (CalculatorModel.cs).
}
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this,new PropertyChangedEventArgs(propertyName));
}
}
}
我想在Model类(CalculatorModel.cs)中定义此计算委托。根据我的理解,这是Model类的含义。 ( 如果我错了,请纠正我 )。
我这样做是这样的:
public class CalculatorModel
{
#region PROPERTIES
public string FirstValue;
public string SecondValue;
public string Result;
#endregion
//CalculatorViewModel cv = new CalculatorViewModel();
public CalculatorModel()
{
this.Result = "";
this.FirstValue = "";
this.SecondValue = "";
}
public void Calculate()
{
MessageBox.Show("check : " +FirstValue);
Result = (Convert.ToInt32(FirstValue) + Convert.ToInt32(SecondValue)).ToString();
}
}
问题是我不知道为什么在调试Result,FirstValue和SecondValue的值为null时 ,单击按钮时会调用委托calculate()
但是Result中没有更新的输出。
有人可以纠正我在Model类中定义calculate()方法的问题吗?
您似乎没有更新模型中的值。 数据绑定仅在View和ViewModel之间起作用。
private string _firstValue;
public string FirstValue
{
get { return _firstValue; }
set
{
_firstValue = value;
cc.FirstValue = _firstValue; // add this
OnPropertyChanged("FirstValue");
}
}
并为SecondValue做到这一点。 更改命令,以便将结果分配给Result。
这告诉您设置不是最有效或最优雅的。 考虑
使模型实现INPC时,您可以(应该)从VM中完全删除FirstValue,SecondValue和Result。 您可以绑定到模型: Text="{Binding Path=cc.FirstValue, Mode=TwoWay}"
,然后将Model设置为属性:
public CalculatorModel cc { get; set; } // must be a property
否则,“重复”属性的更好模式是:
//private string _firstValue;
public string FirstValue
{
get { return cc.FirstValue; }
set
{
//_firstValue = value;
cc.FirstValue = value; // add this
OnPropertyChanged("FirstValue");
}
}
避免两次存储数据。
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