我遇到过这种情况，我需要从View访问ViewModel中的控件。为了编码将所选项目从ComboBox添加到列表中的方法。
我的问题是如何从View访问ViewModel控件？我应该遵循一定的设计模式来实现这个目标吗？
下面的方法是在后面的View's代码中编码的，我知道如果遵循MVVM模式，由于涉及紧密耦合，这是不好的做法。这就是为什么我的目标是将此方法移到ViewModel。
该方法的目的是从两个ComboBoxes中获取当前选定的项目并添加到Key/Value List：
public void AddGradeSubjectChoiceToList()
{
string SelectedSubjectName = "null data";
int SelectedPoints = 01;
SelectedSubjectName = subjectCmbBx.SelectedItem.ToString();
try {
SelectedPoints = int.Parse(ordinaryGradeCmbBx.SelectedValue.ToString());
}
catch (Exception e)
{
//log error here..
}
List<StringKeyValue> SubjectPointKVTemp = new List<StringKeyValue>();
//Add selected pair to list
SubjectPointKVTemp.Add(new StringKeyValue { Key = SelectedSubjectName, Value = SelectedPoints });
SubjectPointKV = SubjectPointKVTemp;
}
MainPage的XAML设置如下，有两个组合框，用于主题和成绩。以及addGrade按钮将调用方法将所选对添加到列表中：
<Page x:Class="LC_Points.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:Core="using:Microsoft.Xaml.Interactions.Core"
xmlns:Interactivity="using:Microsoft.Xaml.Interactivity"
xmlns:converter="using:LC_Points.Converter"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:local="using:LC_Points"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
DataContext="{Binding Source={StaticResource Locator}}"
mc:Ignorable="d">
<Page.Resources>
<converter:BoolToVisibilityConverter x:Key="BoolToVisibilityConverter" />
<converter:BoolToNonVisibilityConverter x:Key="BoolToNonVisibilityConverter" />
</Page.Resources>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="40*" />
<RowDefinition Height="20*" />
<RowDefinition Height="30*" />
<RowDefinition Height="30*" />
<RowDefinition Height="20*" />
<RowDefinition Height="20*" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="4*" />
<ColumnDefinition Width="3*" />
</Grid.ColumnDefinitions>
<ComboBox x:Name="subjectCmbBx"
Grid.Row="1"
Grid.ColumnSpan="2"
Width="174"
HorizontalAlignment="Left"
VerticalAlignment="Top"
DisplayMemberPath="Subject"
Header="Subjects"
ItemsSource="{Binding Subjects}"
PlaceholderText="Pick a subject" />
<ComboBox x:Name="ordinaryGradeCmbBx"
Grid.Row="1"
Grid.Column="0"
Grid.ColumnSpan="2"
Width="170"
HorizontalAlignment="Right"
DisplayMemberPath="Key"
Header="Grades"
ItemsSource="{Binding OrdinaryGradePointKV}"
PlaceholderText="Pick a grade"
Visibility="{Binding IsHigherToggled,
Mode=TwoWay,
Converter={StaticResource BoolToNonVisibilityConverter}}" />
<Button x:Name="addGradeBtn"
Grid.Row="2"
HorizontalAlignment="Left"
Command="{Binding Path=AddGradeCommand}"
Content="Add Grade" />
<ToggleButton x:Name="ordinaryTglBtn"
Grid.Row="3"
Grid.ColumnSpan="2"
HorizontalAlignment="Center"
Content="Ordinary"
IsChecked="{Binding IsOrdinaryToggled,
Mode=TwoWay}" />
</Grid>
</Page>
ViewModel的精简实现如下以供参考，在评论中显示我如何平移实施AddGradeSubjectChoiceToList()方法：
namespace LC_Points.ViewModel
{
public class MainViewModel : ViewModelBase
{
private ScoreModel _scoreModel;
/// <summary>
/// Initializes a new instance of the MainViewModel class.
/// </summary>
public MainViewModel(ScoreModel GradeModel)
{
_scoreModel = GradeModel;
//call methods to initilise list data
GetSubjectTypes();
GetOrdinaryGradePairs();
}
public List<ScoreModel> Subjects { get; set; }
public List<StringKeyValue> OrdinaryGradePointKV { get; set; }
//ordinary toggle button bool
private bool _isOrdinaryToggled;
public bool IsOrdinaryToggled
{
get
{
return _isOrdinaryToggled;
}
set
{
_isOrdinaryToggled = value;
RaisePropertyChanged("IsOrdinaryToggled");
}
}
//Need to add same method from code behind to VM here
//but don't have access to the View's controlsMethod to store Subject and Grade from Combo Boxes
public void AddGradeSubjectChoiceToList()
{
}
//This Relay Command is tied to the button in the View, that will be used
//to call the AddGradeSubjectChoiceToList method
RelayCommand addGradeCommand;
public RelayCommand AddGradeCommand
{
get
{
if (addGradeCommand == null)
{
addGradeCommand = new RelayCommand(() =>
{
AddGradeSubjectChoiceToList
});
}
return addGradeCommand;
}
}
public class StringKeyValue
{
public string Key { get; set; }
public int Value { get; set; }
}
public void GetOrdinaryGradePairs()
{
List<StringKeyValue> ordinaryGradePointKVTemp = new List<StringKeyValue>();
ordinaryGradePointKVTemp.Add(new StringKeyValue { Key = "A1", Value = 60 });
ordinaryGradePointKVTemp.Add(new StringKeyValue { Key = "A2", Value = 50 });
ordinaryGradePointKVTemp.Add(new StringKeyValue { Key = "B1", Value = 45 });
ordinaryGradePointKVTemp.Add(new StringKeyValue { Key = "B2", Value = 40 });
ordinaryGradePointKVTemp.Add(new StringKeyValue { Key = "B3", Value = 35 });
ordinaryGradePointKVTemp.Add(new StringKeyValue { Key = "C1", Value = 30 });
ordinaryGradePointKVTemp.Add(new StringKeyValue { Key = "C2", Value = 25 });
ordinaryGradePointKVTemp.Add(new StringKeyValue { Key = "C3", Value = 20 });
OrdinaryGradePointKV = ordinaryGradePointKVTemp;
}
public void GetSubjectTypes()
{
List<ScoreModel> subjectList = new List<ScoreModel>();
// Adding Subjects to List
subjectList.Add(new ScoreModel { Subject = "Accounting" });
subjectList.Add(new ScoreModel { Subject = "Agricultural Economics" });
subjectList.Add(new ScoreModel { Subject = "Agricultural Science" });
subjectList.Add(new ScoreModel { Subject = "Ancient Greek" });
subjectList.Add(new ScoreModel { Subject = "Applied Math" });
subjectList.Add(new ScoreModel { Subject = "Arabic" });
subjectList.Add(new ScoreModel { Subject = "Art" });
subjectList.Add(new ScoreModel { Subject = "Artistic & Creative Group" });
subjectList.Add(new ScoreModel { Subject = "Biology" });
subjectList.Add(new ScoreModel { Subject = "Business" });
Subjects = subjectList;
}
}
}
答案 0 :(得分：0)
正如上面的评论指出的那样，在遵循MVVM模式时，将View与ViewModel耦合的解决方案是不好的做法。
适当的解决方案是为ComboBox的SelectedItem设置一个属性，并将View绑定到该属性，以便所选项可用于在VM中利用。
1。在查看中设置与 SelectedItem 的绑定：
SelectedItem="{Binding SelectedSubject,Mode=TwoWay}"
2. 在 ViewModel 中创建ComboBox属性：
private ComboBox _selectedSubject;
public ComboBox SelectedSubject
{
get { return _selectedSubject; }
set
{
_selectedSubject = value;
RaisePropertyChanged("SelectedSubject");
}
}
答案 1 :(得分：0)
为了遵循MVVM，您应该使用泛型类型并将它们绑定到控件。
以下是我的一个ViewModel中的示例：
private string[] _optionItems;
public string[] OptionItems
{
get
{
return _optionItems;
}
set
{
if (_optionItems == value)
return;
_optionItems = value;
OnPropertyChanged();
}
}
private string _selectedOption;
public string SelectedOption
{
get
{
return _selectedOption;
}
set
{
if (_selectedOption == value)
return;
_selectedOption = value;
OnPropertyChanged();
}
}
这是XAML代码：
<ComboBox ItemsSource="{Binding OptionItems}" SelectedItem="{Binding SelectedOption}"/>