LoongCore 深入理解MVVM
最好的深入了解，动手实践
文章目录
个人手撸, 并通过单元测试来了解MVVM框架的内涵
12.Abstract和单元测试初体验
- 定义ObservableObject类
由于这是我们将来ViewModel的基类，所以它并没有实际含义，应该定为抽象类，但此处故意忘记
public class ObservableObject : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
}
-
新建单元测试
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在单元测试项目中确认ObservableObject为抽象类
[TestClass]
public class ObservableObject_Test
{
[TestMethod]
public void IsAbstract() {
var type = typeof(ObservableObject);
Assert.IsTrue(type.IsAbstract);
}
}
-
在测试资源管理器中运行测试
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修改ObservableObject后测试通过
public abstract class ObservableObject : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
}
13.PropertyChanged属性改变时发生了什么
ObservableObject.cs属性改变时引发事件的底层方法
// TODO: 13-1 引发属性改变事件的方法
/// <summary>
/// 引发属性改变事件
/// </summary>
/// <param name="propertyName">发生改变的属性的名称</param>
/// <remarks>
/// ?. 操作符如果有人给ViewModel留了“名片”才会引发，即外部有人订阅了PropertyChanged
/// 没有这个方法是可以的，但是你可能得硬编码写propertyName
/// </remarks>
protected void RaisePropertyChanged([CallerMemberName] string propertyName = null)
=> PropertyChanged?.Invoke
(
this,
new PropertyChangedEventArgs(propertyName)
);
ObservableObject.cs属性设置器，当待设置的值确实为新值时会调用RaisePropertyChanged
// TODO: 13-2 属性设置器
/// <summary>
/// 设置新的属性值,如果是“真的新”，调用<seealso cref="RaisePropertyChanged(string)"/>
/// </summary>
/// <typeparam name="T">目标属性的类型</typeparam>
/// <param name="target">目标属性</param>
/// <param name="value">可能是新的值</param>
/// <param name="propertyName">[不要设置]目标属性的名称，自动推断</param>
/// <returns>[true]目标属性已被更新？</returns>
protected bool SetProperty<T>
(
ref T target, // 目标属性
T value, // “新”值
[CallerMemberName] string propertyName = null
) {
if (EqualityComparer<T>.Default.Equals(target, value))
return false;
target = value;
RaisePropertyChanged(propertyName);
return true;
}
- 单元测试
using System;
using Microsoft.VisualStudio.TestTools.UnitTesting;
// TODO: 13-3 引用Logger记录器
using LoongEgg.LoongLogger;
namespace LoongEgg.LoongCore.Test
{
[TestClass]
public class ObservableObject_Test
{
// TODO: 13-4 测试初始化
/// <summary>
/// 初始化测试，会在所有测试方法前调用
/// </summary>
/// <remarks>
/// LoongEgg.LoongLogger是我的一个开源项目，你可以不使用
/// </remarks>
[TestInitialize]
public void EnabledLogger() {
LoggerManager.Enable(LoggerType.File, LoggerLevel.Debug);
}
/// <summary>
/// 抽象类确认
/// </summary>
[TestMethod]
public void IsAbstract() {
var type = typeof(ObservableObject);
Assert.IsTrue(type.IsAbstract);
}
// TODO: 13-5 设计一个测试类
/// <summary>
/// <see cref="ObservableObject"/>的一个测试样本
/// </summary>
public class ObservableObjectSample : ObservableObject
{
/// <summary>
/// 测试属性
/// </summary>
public int PropertySample {
get => _PropertySample;
set => SetProperty(ref _PropertySample, value);
}
/// <summary>
/// 测试字段
/// </summary>
private int _PropertySample;
}
// TODO: 13-6 属性改变时会发生什么
/// <summary>
/// 属性改变，且会引发事件确认
/// </summary>
[TestMethod]
public void CanPropertyChangedRaised() {
bool isPropertyChangeRaised = false;// 事件引发标记
// 初始化一个检测样本
ObservableObjectSample sample = new ObservableObjectSample();
// 注册属性改变时的处理事件
sample.PropertyChanged += (s, args) =>
{
isPropertyChangeRaised = true;
LoggerManager.WriteDebug($"PropertyName:{args.PropertyName}");
};
// 改变属性
sample.PropertySample = 666;
Assert.IsTrue(isPropertyChangeRaised);
Assert.AreEqual(sample.PropertySample, 666);
}
// TODO: 13-7 清理测试环境
/// <summary>
/// 在所有测试完成后调用，注销LoggerManager
/// </summary>
[TestCleanup]
public void DisableLogger() {
LoggerManager.WriteDebug("LoggerManager is clean up...");
LoggerManager.Disable();
}
}
}
14.在正确的时机引发通知
- 属性不真正改变的时候不要引发事件
// TODO: 14-1 当“新值”等于当前值时不引发通知
/// <summary>
/// 当“新值”等于当前值时不引发通知
/// </summary>
public void WhenPropertyEqualsOldValue_NotRaised() {
bool isPropertyChangeRaised = false;// 事件引发标记
// 初始化一个检测样本
// 注意这里赋了一个初始值
ObservableObjectSample sample = new ObservableObjectSample { PropertySample = 666};
// 注册属性改变时的处理事件
sample.PropertyChanged += (s, args) =>
{
isPropertyChangeRaised = true;
LoggerManager.WriteDebug(
$"Event is raised by PropertyName={args.PropertyName}, value={sample.PropertySample}");
};
// 改变属性
sample.PropertySample = 666;
Assert.IsFalse(isPropertyChangeRaised); // 注意这里断言是Flase
Assert.AreEqual(sample.PropertySample, 666);
}
- 创建ViewModelBase.cs
// TODO: 14-2 设计ViewModel的基类
/// <summary>
/// ViewModel们继承于此
/// </summary>
public abstract class ViewModelBase : ObservableObject { }
- 依赖于它人的属性改变事件，由被依赖者引发
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在ViewModelBase_Test.cs增加测试类
public class People: ViewModelBase
{
public string FamilyName {
get => _FamilyName;
set {
if (SetProperty(ref _FamilyName, value))
RaisePropertyChanged("FullName");
}
}
private string _FamilyName = "[NotDefined]";
public string LastName {
get => _LastName;
set {
if (SetProperty(ref _LastName, value))
RaisePropertyChanged(nameof(FullName));
}
}
private string _LastName = "[Unknown]";
public string FullName => $"{FamilyName} - {LastName}";
}
4.完整的单元测试
using System;
using LoongEgg.LoongLogger;
using Microsoft.VisualStudio.TestTools.UnitTesting;
namespace LoongEgg.LoongCore.Test
{
[TestClass]
public class ViewModelBase_Test
{ /// <summary>
/// 初始化测试，会在所有测试方法前调用
/// </summary>
/// <remarks>
/// LoongEgg.LoongLogger是我的一个开源项目，你可以不使用
/// </remarks>
[TestInitialize]
public void EnabledLogger() {
LoggerManager.Enable(LoggerType.File, LoggerLevel.Debug);
LoggerManager.WriteDebug("Test initialized ok ....");
}
// TODO: 14-3设计测试类People
public class People: ViewModelBase
{
public string FamilyName {
get => _FamilyName;
set {
if (SetProperty(ref _FamilyName, value))
RaisePropertyChanged("FullName");
}
}
private string _FamilyName = "[NotDefined]";
public string LastName {
get => _LastName;
set {
if (SetProperty(ref _LastName, value))
RaisePropertyChanged(nameof(FullName));
}
}
private string _LastName = "[Unknown]";
public string FullName => $"{FamilyName} - {LastName}";
}
// TODO: 14-4 检查可以强制引发属性改变事件
[TestMethod]
public void CanRaisedByOtherProperty() {
People people = new People();
bool isRaised = false;
people.PropertyChanged += (s, e) =>
{
isRaised = true;
if(e.PropertyName == "FullName") {
LoongLogger.LoggerManager.WriteDebug($"FullName is changed to -> {people.FullName}");
}
};
people.FamilyName = "Alpha";
people.LastName = "Jet";
Assert.IsTrue(isRaised);
}
/// <summary>
/// 在所有测试完成后调用，注销LoggerManager
/// </summary>
[TestCleanup]
public void DisableLogger() {
LoggerManager.WriteDebug("LoggerManager is clean up...");
LoggerManager.Disable();
}
}
}
15.ICommand命令的实现
- ICommand的实现
DelegateCommand.cs
using System;
using System.Windows.Input;
/*
| 个人微信：InnerGeeker
| 联系邮箱：[email protected]
| 创建时间：2020/4/12 18:28:22
| 主要用途：
| 更改记录：
| 时间 版本 更改
*/
namespace LoongEgg.LoongCore
{
public class DelegateCommand : ICommand
{
/*---------------------------------------- Fields ---------------------------------------*/
/// <summary>
/// 干活的方法
/// </summary>
private readonly Action<object> _Execute;
/// <summary>
/// 判断可以干活的方法
/// </summary>
private readonly Predicate<object> _CanExecute;
public bool CanExecuteCache { get; private set; } = true;
/*------------------------------------- Constructors ------------------------------------*/
/// <summary>
/// 主构造器
/// </summary>
/// <param name="execute">干活的方法</param>
/// <param name="canExecute">判断可以干活的方法</param>
public DelegateCommand(Action<object> execute, Predicate<object> canExecute) {
_Execute = execute ?? throw new ArgumentNullException("execute 不能为空");
_CanExecute = canExecute;
}
/// <summary>
/// 构造器
/// </summary>
/// <param name="execute">干活的方法</param>
public DelegateCommand(Action<object> execute) : this(execute, null) { }
public event EventHandler CanExecuteChanged;
/*------------------------------------ Public Methods -----------------------------------*/
/// <summary>
/// 检查是否可以执行命令
/// </summary>
/// <param name="parameter"></param>
/// <returns></returns>
public bool CanExecute(object parameter) {
bool canExecute = _CanExecute?.Invoke(parameter) ?? true;
if(canExecute != CanExecuteCache) {
CanExecuteCache = canExecute;
RaiseCanExecuteChanged();
}
return canExecute;
}
/// <summary>
/// 执行命令操作
/// </summary>
/// <param name="parameter"></param>
public void Execute(object parameter) => _Execute(parameter);
/// <summary>
/// 引发可执行改变事件
/// </summary>
public void RaiseCanExecuteChanged() => CanExecuteChanged?.Invoke(this, EventArgs.Empty);
}
}
2.DelegateCommand的单元测试
using System;
using LoongEgg.LoongLogger;
using Microsoft.VisualStudio.TestTools.UnitTesting;
namespace LoongEgg.LoongCore.Test
{
[TestClass]
public class DelegateCommand_Test
{
/// <summary>
/// 初始化测试，会在所有测试方法前调用
/// </summary>
/// <remarks>
/// LoongEgg.LoongLogger是我的一个开源项目，你可以不使用
/// </remarks>
[TestInitialize]
public void EnabledLogger() {
LoggerManager.Enable(LoggerType.File, LoggerLevel.Debug);
LoggerManager.WriteDebug("Test initialized ok ....");
}
/// <summary>
/// 检查在构造器中execute不能为null
/// </summary>
[TestMethod]
[ExpectedException(typeof(ArgumentNullException))]
public void Constructor_ThrowExectptionIfActionParameterIsNull() {
var command = new DelegateCommand(null);
}
/// <summary>
/// Action可以被正常委托执行
/// </summary>
[TestMethod]
public void ExecuteAction_CanInvokes() {
bool invoked = false;
void action(object obj) => invoked = true;
var command = new DelegateCommand(action);
command.Execute(null);
Assert.IsTrue(invoked);
}
/// <summary>
/// CanExecute为Null时命令默认可以执行
/// </summary>
[TestMethod]
public void CanExecute_IsTrueByDefault() {
var command = new DelegateCommand(obj => { });
Assert.IsTrue(command.CanExecute(null));
}
/// <summary>
/// CanExecute可以判断命令不能执行
/// </summary>
[TestMethod]
public void CanExecute_FalsePredicate() {
var command = new DelegateCommand
(
obj => { },
obj => (int)obj == 0
);
Assert.IsFalse(command.CanExecute(6));
}
/// <summary>
/// CanExecute可以判断命令可以执行
/// </summary>
[TestMethod]
public void CanExecute_TruePredicate() {
var command = new DelegateCommand
(
obj => { },
obj => (int)obj == 6
);
Assert.IsTrue(command.CanExecute(6));
}
[TestMethod]
public void CanExecuteChanged_Raised() {
var command = new DelegateCommand
(
obj => { },
obj => (int)obj == 6
);
bool isCanExecuteChanged = false;
command.CanExecuteChanged += (s, e) =>
{
isCanExecuteChanged = true;
LoggerManager.WriteDebug($"CanExecuteChanged Raised by {s.ToString()}");
};
Assert.IsTrue(command.CanExecute(6));
Assert.IsFalse(command.CanExecute(66));
Assert.IsTrue(isCanExecuteChanged);
}
/// <summary>
/// 在所有测试完成后调用，注销LoggerManager
/// </summary>
[TestCleanup]
public void DisableLogger() {
LoggerManager.WriteDebug("LoggerManager is clean up...");
LoggerManager.Disable();
}
}
}
16.我的MVVM项目结构与在控制台启动WPF
1.我的项目结构
AppConsole控制台程序，负责组装View和ViewModelLoongEgg.LoongCore普通类库，MVVM核心框架，提供了ViewModel的基类LoongEgg.LoongCore.Test核心框架的单元测试项目LoongEgg.ViewModels普通类库，ViewModel们在这里设计，小项目也负责处理业务逻辑LoongEgg.ViewModels.TestViewModel们的单元测试LoongEgg.Views自定义控件库，View们在这集设计
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2.在控制台启动WPF窗口
- 须要的引用
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using LoongEgg.ViewModels;
using LoongEgg.Views;
using System;
using System.Windows;
namespace AppConsole
{
class Program
{
[STAThread]
static void Main(string[] args) {
//CalculatorViewModel viewModel = new CalculatorViewModel { Left = 111, Right = 222, Answer = 333 };
CalculatorView view = new CalculatorView { DataContext = viewModel };
Application app = new Application();
app.Run(view);
}
}
}
17.没有MVVM
MainWindow.xaml前台代码
<Window
x:Class="NoMVVM.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:NoMVVM"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
Title="MainWindow"
Width="800"
Height="450"
FontSize="32"
mc:Ignorable="d">
<Grid Margin="5">
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition Width="AUTO" />
<ColumnDefinition />
<ColumnDefinition Width="AUTO" />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<!-- 左侧操作数 -->
<TextBox
x:Name="left"
Grid.Column="0"
VerticalAlignment="Center"
Text="666" />
<!-- 运算符们 -->
<StackPanel
Grid.Column="1"
VerticalAlignment="Center"
ButtonBase.Click="Button_Click">
<Button
Width="80"
Height="80"
Margin="5"
Content="+" />
<Button
Width="80"
Height="80"
Margin="5"
Content="-" />
<Button
Width="80"
Height="80"
Margin="5"
Content="*" />
<Button
Width="80"
Height="80"
Margin="5"
Content="/" />
</StackPanel>
<!-- 右侧操作数 -->
<TextBox
x:Name="right"
Grid.Column="2"
VerticalAlignment="Center"
Text="999" />
<!-- =号 -->
<Label
Grid.Column="3"
VerticalAlignment="Center"
Content="=" />
<TextBlock
x:Name="answer"
Grid.Column="4"
VerticalAlignment="Center"
Text="Answer" />
</Grid>
</Window>
MainWindow.xaml.cs后端代码
using System.Windows;
using System.Windows.Controls;
namespace NoMVVM
{
/// <summary>
/// MainWindow.xaml 的交互逻辑
/// </summary>
public partial class MainWindow : Window
{
public MainWindow() {
InitializeComponent();
}
private void Button_Click(object sender, RoutedEventArgs e) {
if(e.Source is Button btn) {
bool isDouble = false;
isDouble = double.TryParse( left.Text, out double leftOpr);
if (!isDouble) return;
isDouble = double.TryParse( right.Text, out double rightOpr);
if (!isDouble) return;
string opr = btn.Content.ToString();
switch (opr) {
case "+":answer.Text = (leftOpr + rightOpr).ToString(); break;
case "-":answer.Text = (leftOpr - rightOpr).ToString(); break;
case "*":answer.Text = (leftOpr * rightOpr).ToString(); break;
case "/":answer.Text = (leftOpr / rightOpr).ToString(); break;
default:
break;
}
}
}
}
}
18.第一个ViewModel简易计算器
- 计算器的ViewModel
using LoongEgg.LoongCore;
using System.Windows.Controls;
using System.Windows.Input;
namespace LoongEgg.ViewModels
{
// TODO: 18-1 计算器的ViewModel
/// <summary>
/// 计算器的ViewModel
/// </summary>
public class CalculatorViewModel: ViewModelBase
{
/*------------------------------------- Properties --------------------------------------*/ /// <summary>
/// 左侧操作数
/// </summary>
public int Left {
get => _Left;
set => SetProperty(ref _Left, value);
}
protected int _Left;
/// <summary>
/// 右侧操作数
/// </summary>
public int Right {
get => _Right;
set => SetProperty(ref _Right, value);
}
protected int _Right;
/// <summary>
/// 计算结果
/// </summary>
public int Answer {
get => _Answer;
set => SetProperty(ref _Answer, value);
}
protected int _Answer;
/// <summary>
/// 运算命令
/// </summary>
public ICommand OperationCommand { get; protected set; }
/*------------------------------------- Constructor -------------------------------------*/
/// <summary>
/// 默认构造器
/// </summary>
public CalculatorViewModel() {
OperationCommand = new DelegateCommand(Operation);
}
/*----------------------------------- Private Methods -----------------------------------*/
/// <summary>
/// 运算的具体执行方法
/// </summary>
/// <param name="opr"></param>
protected void Operation(object opr) {
var self = opr as Button;
switch (opr.ToString()) {
case "+": Answer = Left + Right; break;
case "-": Answer = Left - Right; break;
case "*": Answer = Left * Right; break;
case "/": Answer = Left / Right; break;
};
}
}
}
- CalculatorViewModel的单元测试
using System;
using Microsoft.VisualStudio.TestTools.UnitTesting;
namespace LoongEgg.LoongCore.Test
{
// TODO: 15-2 DelegateCommand的单元测试
[TestClass]
public class DelegateCommand_Test
{
[TestMethod]
[ExpectedException(typeof(ArgumentNullException))]
public void Constructor_ThrowExeceptionIfExecuteParameterIsNULL() {
var command = new DelegateCommand(null);
}
[TestMethod]
public void Execute_CanInvokes() {
bool invoked = false;
var command = new DelegateCommand(
obj => { invoked = true; }
);
command.Execute(null);
Assert.IsTrue(invoked);
}
[TestMethod]
public void CanExecute_IsTrueByDefault() {
var command = new DelegateCommand(obj => { });
Assert.IsTrue( command.CanExecute(null));
}
[TestMethod]
public void CanExecute_TruePredicate() {
var command = new DelegateCommand
(
obj => { },
obj => (int)obj == 666
);
Assert.IsTrue(command.CanExecute(666));
}
[TestMethod]
public void CanExecute_FalsePredicate() {
var command = new DelegateCommand
(
obj => { },
obj => (int)obj == 666
);
Assert.IsFalse(command.CanExecute(66));
}
}
}
19.ViewModel和View的会师，Binding前建议必看这个视频
https://www.bilibili.com/video/BV1ci4y1t7D6/
KeyPoint
- 在控制台启动WPF并设置DataContext为你的ViewModel
- DesignModel继承ViewModel但因为有类型为自己的静态属性，可以设计时绑定，减小出错概率
- 命令的绑定不要忘记绑定CommandParameter(如果需要)
1.初始化ViewModel并注入View(依赖注入)
using LoongEgg.ViewModels;
using LoongEgg.Views;
using System;
using System.Windows;
namespace AppConsole
{
class Program
{
[STAThread]
static void Main(string[] args) {
// TODO: 19-1 初始化ViewModel并注入View
// 初始化一个ViewModel并设置一些初始值以示和DesignModel不一样
CalculatorViewModel viewModel = new CalculatorViewModel { Left = 111, Right = 222, Answer = 333 };
// 将ViewModel赋值给View的DataContext
CalculatorView view = new CalculatorView { DataContext = viewModel };
Application app = new Application();
app.Run(view);
}
}
}
2.创建一个DesignModel以方便设计时绑定
using LoongEgg.ViewModels;
namespace LoongEgg.Views
{
/*
|
| WeChat: InnerGeek
| [email protected]
|
*/
// TODO: 19-2 创建一个DesignModel以方便设计时绑定
public class CalculatorDesignModel: CalculatorViewModel
{
public static CalculatorDesignModel Instance => _Instance ?? (_Instance = new CalculatorDesignModel());
private static CalculatorDesignModel _Instance;
public CalculatorDesignModel() : base() {
Left = 999;
Right = 666;
Answer = 233;
}
}
}
3.完成View和ViewModel在Xaml中的绑定
不要忘了设置设计时DataContextd:DataContext="{x:Static local:CalculatorDesignModel.Instance}"
Binding你会发现，哦哟，有语法提示了
<Window
x:Class="LoongEgg.Views.CalculatorView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:LoongEgg.Views"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:vm="clr-namespace:LoongEgg.ViewModels;assembly=LoongEgg.ViewModels"
Title="Calculator View - 1st MVVM Application"
Width="800"
Height="450"
d:DataContext="{x:Static local:CalculatorDesignModel.Instance}"
FontSize="52"
WindowStartupLocation="CenterScreen"
mc:Ignorable="d">
<Window.Resources>
<Style TargetType="{x:Type Button}">
<Setter Property="Width" Value="80" />
<Setter Property="Height" Value="80" />
<Setter Property="Margin" Value="5" />
</Style>
<Style TargetType="{x:Type TextBox}">
<Setter Property="HorizontalAlignment" Value="Stretch" />
<Setter Property="VerticalAlignment" Value="Center" />
</Style>
</Window.Resources>
<Grid Margin="5">
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition Width="auto" />
<ColumnDefinition />
<ColumnDefinition Width="auto" />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<!-- 左侧的操作数 -->
<TextBox Grid.Column="0" Text="{Binding Left}" />
<!-- 运算符们 -->
<StackPanel Grid.Column="1" VerticalAlignment="Center">
<Button
Command="{Binding OperationCommand}"
CommandParameter="+"
Content="+" />
<Button
Command="{Binding OperationCommand}"
CommandParameter="-"
Content="-" />
<Button
Command="{Binding OperationCommand}"
CommandParameter="*"
Content="*" />
<Button
Command="{Binding OperationCommand}"
CommandParameter="/"
Content="/" />
</StackPanel>
<!-- 右侧操作数 -->
<TextBox Grid.Column="2" Text="{Binding Right}" />
<Label
Grid.Column="3"
VerticalAlignment="Center"
Content="=" />
<!-- 计算结果 -->
<TextBox Grid.Column="4" Text="{Binding Answer}" />
</Grid>
</Window>
20.全网最简单的IValueConverter实现
1.一般方法的IValueConverter类
using System;
using System.Globalization;
using System.Windows.Data;
using System.Windows.Media;
/*
| 个人微信：InnerGeeker
| 联系邮箱：[email protected]
| 创建时间：2020/4/14 19:51:26
| 主要用途：
| 更改记录：
| 时间 版本 更改
*/
namespace LoongEgg.Views
{
/// <summary>
/// 整型转<see cref="Brush"/>
/// </summary>
public class IntToBrushConverter : IValueConverter
{
/*------------------------------------ Public Methods -----------------------------------*/
/// <summary>
/// 整数转<see cref="Brush"/><see cref="IValueConverter.Convert(object, Type, object, CultureInfo)"/>
/// </summary>
public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
if (value == null) {
return null;
}else if((int) value < 18) {
return Brushes.Green;
}else {
return Brushes.Blue;
}
}
/// <summary>
/// 不重要
/// </summary>
public object ConvertBack
(
object value,
Type targetType,
object parameter,
CultureInfo culture
) => throw new NotImplementedException();
}
}
2.一般方法的IValueConverter使用
- 定义为静态资源
<Window.Resources>
<local:IntToBrushConverter x:Key="intToBrushConverter" />
</Window.Resources>
- 在你需要的地方静态引用
<!-- 左侧的操作数 -->
<TextBox
Grid.Column="0"
Foreground="{Binding Left, Converter={StaticResource intToBrushConverter}}"
Text="{Binding Left}" />
3.一劳永逸的IValueConverter基类
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Data;
using System.Windows.Markup;
/*
| 个人微信：InnerGeeker
| 联系邮箱：[email protected]
| 创建时间：2020/4/14 20:07:32
| 主要用途：
| 更改记录：
| 时间 版本 更改
*/
namespace LoongEgg.Views
{
/// <summary>
/// 值转换器的基类，是一个泛型方法，传入你要实现的值转换本身
/// </summary>
/// <typeparam name="T">你要的值转换器它本身类型</typeparam>
public abstract class BaseValueConverter <T>
: MarkupExtension, IValueConverter
where T: class, new()
{
/*---------------------------------------- Fields ---------------------------------------*/
/// <summary>
/// 值转换器的实例
/// </summary>
private static T _Instance;
/*------------------------------------ Public Methods -----------------------------------*/
/// <summary>
/// 为了在Xaml中直接使用<see cref="IValueConverter"/>必须实现的一个方法<see cref="MarkupExtension.ProvideValue(IServiceProvider)"/>
/// </summary>
/// <param name="serviceProvider"></param>
/// <returns>返回值转换器的单实例</returns>
public override object ProvideValue(IServiceProvider serviceProvider)
=> _Instance ?? (_Instance = new T());
/// <summary>
/// <see cref="IValueConverter.Convert(object, Type, object, CultureInfo)"/>
/// </summary>
/// <param name="value"></param>
/// <param name="targetType"></param>
/// <param name="parameter"></param>
/// <param name="culture"></param>
/// <returns></returns>
public abstract object Convert(object value, Type targetType, object parameter, CultureInfo culture);
/// <summary>
/// 将前台UI中的值转换给后台ViewModel一般用不上
/// </summary>
/// <param name="value">UI中的值</param>
/// <param name="targetType">目标类型</param>
/// <param name="parameter">额外的转换参数</param>
/// <param name="culture"></param>
/// <returns></returns>
public virtual object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
=> throw new NotImplementedException();
}
}
4.ValueConverter的最简单实现
using System;
using System.Globalization;
using System.Windows.Media;
/*
| 个人微信：InnerGeeker
| 联系邮箱：[email protected]
| 创建时间：2020/4/14 20:18:51
| 主要用途：
| 更改记录：
| 时间 版本 更改
*/
namespace LoongEgg.Views
{
/// <summary>
/// 最简单的值转换器实现
/// </summary>
public class AdvanceIntToBrushConverter : BaseValueConverter<AdvanceIntToBrushConverter>
{
/*------------------------------------ Public Methods -----------------------------------*/
public override object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
if (value == null) {
return null;
}else if( (int) value < 18) {
return Brushes.Green;
}else {
return Brushes.Yellow;
}
}
}
}
5.最简单的ValueConverter使用
<!-- 右侧操作数 -->
<TextBox
Grid.Column="2"
Background="{Binding Right, Converter={local:AdvanceIntToBrushConverter}}"
Text="{Binding Right}" />