UWP控件与DataBind

　　在uwp开发中必不可少的一个环节就是各种通用的控件的开发，所以在闲暇时间汇总了一下在uwp开发中控件的几种常用写法，以及属性的几种绑定方式，有可能不全面，请大家多多包涵 :)

1、先从win10新增的{x:Bind}绑定方式说起，相对于{Binding}，{x:Bind}在时间复杂度和空间复杂度上都要降低不少。但并不是说{x:Bind}能够完全取代{Binding}，因为{x:Bind} 比 {Binding} 少了许多功能，例如 Source、UpdateSourceTrigger等，并且不支持后台C#代码编写，所以使用者还是要根据自己的需求来选择用哪种方式，下面是Control1的简单实现

Control1.xaml

<UserControl  x:Class="Controls.Control1"  ="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  ="http://schemas.microsoft.com/winfx/2006/xaml"  ="using:Controls"  ="http://schemas.microsoft.com/expression/blend/2008"  ="http://schemas.open"  mc:Ignorable="d"  d:DesignHeight="300"  d:DesignWidth="400">  <Grid>    <TextBlock Text="{x:Bind Text}"></TextBlock>  </Grid></UserControl>

Control1.xaml.cs

using Windows.UI.Xaml.Controls;// The User Control item template is documented at http://go.microsoft.com/fwlink/?LinkId=234236namespace Controls{  public sealed partial class Control1 : UserControl  {    public Control1()    {      this.InitializeComponent();    }    public string Text { set; get; }  }}

使用方式

<Page  x:Class="Controls.MainPage"  ="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  ="http://schemas.microsoft.com/winfx/2006/xaml"  ="using:Controls"  ="http://schemas.microsoft.com/expression/blend/2008"  ="http://schemas.open"  mc:Ignorable="d"  ="using:Controls">  <StackPanel Background="{ThemeResource ApplicationPageBackgroundThemeBrush}" Margin="40">    <controls:Control1 Text="这是控件1"></controls:Control1>  </StackPanel></Page>

　　值得一提是{x:Bind}在DataTemplate中绑定时是需要指定类型的（x:DataType），并且Mode默认是OneTime，所以使用者如果有需要千万不要忘了改成Mode=OneWay或者Mode=TwoWay

<DataTemplate x:DataType="model:Student">    <TextBlock Text="{x:Bind Name}"></TextBlock>    <TextBlock Text="{x:Bind Age}"></TextBlock></DataTemplate>

2、{Binding}绑定方式，大家应该比较熟悉了，它提供了丰富的绑定功能，绑定方式也比较灵活，闲话不多说啦，下面的Control2和Control3的实现

TextVisibilityConverter.cs

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using Windows.UI.Xaml;using Windows.UI.Xaml.Data;namespace Controls.Common{  public class TextVisibilityConverter : IValueConverter  {    public object Convert(object value, Type targetType, object parameter, string language)    {      if(value is string)      {        var text = value as string;                if(string.IsNullOrEmpty(text))        {          return Visibility.Collapsed;        }        else        {          return Visibility.Visible;        }      }      return Visibility.Visible;    }    public object ConvertBack(object value, Type targetType, object parameter, string language)    {      throw new NotImplementedException();    }  }}

Control2.xaml

<UserControl  x:Class="Controls.Control2"  ="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  ="http://schemas.microsoft.com/winfx/2006/xaml"  ="using:Controls"  ="using:Controls.Common"  ="http://schemas.microsoft.com/expression/blend/2008"  ="http://schemas.open"  mc:Ignorable="d"  d:DesignHeight="300"  d:DesignWidth="400">  <UserControl.Resources>    <converter:TextVisibilityConverter x:Name="TextVisibilityConverter"></converter:TextVisibilityConverter>  </UserControl.Resources>  <Grid>    <TextBlock Text="{Binding Text}" Visibility="{Binding Text,Converter={StaticResource TextVisibilityConverter}}"></TextBlock>  </Grid></UserControl>

Control2.xaml.cs

using Windows.UI.Xaml;using Windows.UI.Xaml.Controls;// The User Control item template is documented at http://go.microsoft.com/fwlink/?LinkId=234236namespace Controls{  public sealed partial class Control2 : UserControl  {    public Control2()    {      this.InitializeComponent();      this.DataContext = this;    }    public string Text    {      get { return (string)GetValue(TextProperty); }      set { SetValue(TextProperty, value); }    }    // Using a DependencyProperty as the backing store for Text. This enables animation, styling, binding, etc...    public static readonly DependencyProperty TextProperty =      DependencyProperty.Register("Text", typeof(string), typeof(Control2), new PropertyMetadata(""));  }}

Control3.xaml

<UserControl  x:Class="Controls.Control3"  Name="uc"  ="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  ="http://schemas.microsoft.com/winfx/2006/xaml"  ="using:Controls"  ="http://schemas.microsoft.com/expression/blend/2008"  ="http://schemas.open"  mc:Ignorable="d"  d:DesignHeight="300"  d:DesignWidth="400">  <Grid>    <TextBlock Text="{Binding ElementName=uc,Path=Text}"></TextBlock>  </Grid></UserControl>

Control3.xaml.cs

using System;using System.Collections.Generic;using System.IO;using System.Linq;using System.Runtime.InteropServices.WindowsRuntime;using Windows.Foundation;using Windows.Foundation.Collections;using Windows.UI.Xaml;using Windows.UI.Xaml.Controls;using Windows.UI.Xaml.Controls.Primitives;using Windows.UI.Xaml.Data;using Windows.UI.Xaml.Input;using Windows.UI.Xaml.Media;using Windows.UI.Xaml.Navigation;// The User Control item template is documented at http://go.microsoft.com/fwlink/?LinkId=234236namespace Controls{  public sealed partial class Control3 : UserControl  {    public Control3()    {      this.InitializeComponent();    }    public string Text { set; get; }  }}

大家可以看出Control2和Control3是有些微差别的：

Control2是通过 this.DataContext = this，然后将依赖属性（至于为什么是依赖属性，下面会有详细的介绍）绑到xaml页面的控件属性上

Control3的特点也不难发现，充分利用了{Binding}强大功能的一个小小角落；个人感觉应该提一下的是，如果Control3有一个叫做Control1属性，类型是Control1，我们可以把控件1绑到控件3上面去，这样我们就可以在控件3里访问控件1啦，这个只是{Binding}灵活运用的一个例子

<controls:Control1 x:Name="ctr1" Text="这是控件1"></controls:Control1><controls:Control3 Control1="{Binding ElementName=ctr1}"></controls:Control3>

3、通过依赖属性的PropertyChangedCallback来实现对控件属性赋值，请看示例Control5

Control5.xaml

<UserControl  x:Class="Controls.Control5"  ="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  ="http://schemas.microsoft.com/winfx/2006/xaml"  ="using:Controls"  ="http://schemas.microsoft.com/expression/blend/2008"  ="http://schemas.open"  mc:Ignorable="d"  d:DesignHeight="300"  d:DesignWidth="400">  <Grid>    <TextBlock Name="txt"></TextBlock>  </Grid></UserControl>

Control5.xaml.cs

using Windows.UI.Xaml;using Windows.UI.Xaml.Controls;// The User Control item template is documented at http://go.microsoft.com/fwlink/?LinkId=234236namespace Controls{  public sealed partial class Control5 : UserControl  {    public Control5()    {      this.InitializeComponent();    }    public string Text    {      get { return (string)GetValue(TextProperty); }      set { SetValue(TextProperty, value); }    }    // Using a DependencyProperty as the backing store for Text. This enables animation, styling, binding, etc...    public static readonly DependencyProperty TextProperty =      DependencyProperty.Register("Text", typeof(string), typeof(Control5), new PropertyMetadata("", OnTextChanged));    private static void OnTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)    {      var me = d as Control5;      me.OnTextChanged();    }    private void OnTextChanged()    {      var text = txt.Text = this.Text;      if (string.IsNullOrEmpty(text))      {        txt.Visibility = Visibility.Collapsed;      }      else      {        txt.Visibility = Visibility.Visible;      }    }  }}

　　不用通过任何绑定，就可以实现数据赋值，好处在于更加灵活，实现了与Control2同样的功能，您会不会觉得与使用Converter相比，这样写更加直观和舒服呢，而且很多复杂的功能都可以在OnTextChanged里面处理。当然，并不是说Converter是多余的，如果仅限于“值”的转换，Converter还是很方便的，而且还可以重用。

　　如果我们增加一个属性TextMaxLength，用来表示最多可显示的字符数，这样我们把Control5做一下改装

Control5.xaml

<UserControl  x:Class="Controls.Control5"  ="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  ="http://schemas.microsoft.com/winfx/2006/xaml"  ="using:Controls"  ="http://schemas.microsoft.com/expression/blend/2008"  ="http://schemas.open"  mc:Ignorable="d"  d:DesignHeight="300"  d:DesignWidth="400">  <StackPanel>    <TextBlock Name="txt"></TextBlock>    <TextBlock><Run Text="最多可显示"></Run><Run x:Name="run1" Foreground="Red"></Run><Run Text="个字符"></Run></TextBlock>    <TextBlock><Run Text="还有"></Run><Run x:Name="run2" Foreground="Blue"></Run><Run Text="个字符可以显示"></Run></TextBlock>  </StackPanel></UserControl>

Control5.xaml.cs

using Windows.UI.Xaml;using Windows.UI.Xaml.Controls;// The User Control item template is documented at http://go.microsoft.com/fwlink/?LinkId=234236namespace Controls{  public sealed partial class Control5 : UserControl  {    public Control5()    {      this.InitializeComponent();    }    public int TextMaxLength    {      get { return (int)GetValue(TextMaxLengthProperty); }      set { SetValue(TextMaxLengthProperty, value); }    }    // Using a DependencyProperty as the backing store for TextMaxLength. This enables animation, styling, binding, etc...    public static readonly DependencyProperty TextMaxLengthProperty =      DependencyProperty.Register("TextMaxLength", typeof(int), typeof(Control5),        new PropertyMetadata(int.MaxValue, OnTextChanged));    public string Text    {      get { return (string)GetValue(TextProperty); }      set { SetValue(TextProperty, value); }    }    // Using a DependencyProperty as the backing store for Text. This enables animation, styling, binding, etc...    public static readonly DependencyProperty TextProperty =      DependencyProperty.Register("Text", typeof(string), typeof(Control5),        new PropertyMetadata("", OnTextChanged));    private static void OnTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)    {      var me = d as Control5;      me.OnTextChanged();    }    private void OnTextChanged()    {      run1.Text = TextMaxLength.ToString();      if (string.IsNullOrEmpty(this.Text))      {        txt.Visibility = Visibility.Collapsed;      }      else      {        txt.Visibility = Visibility.Visible;        var len = this.Text.Length;        if (len <= TextMaxLength)        {          txt.Text = this.Text;          run2.Text = (TextMaxLength - len).ToString();        }        else        {          txt.Text = this.Text.Remove(TextMaxLength);          run2.Text = "0";        }      }    }  }}

使用方式

<Page  x:Class="Controls.MainPage"  ="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  ="http://schemas.microsoft.com/winfx/2006/xaml"  ="using:Controls"  ="http://schemas.microsoft.com/expression/blend/2008"  ="http://schemas.open"  mc:Ignorable="d"  ="using:Controls">  <StackPanel Background="{ThemeResource ApplicationPageBackgroundThemeBrush}" HorizontalAlignment="Center" Margin="40">    <controls:Control5 x:Name="control5" TextMaxLength="10" Text="这是控件5"></controls:Control5>  </StackPanel></Page>

运行结果

　　需求好无厘头啊，不过确实体现出了通过PropertyChangedCallback来处理实现两种或两种以上属性间“联动”（我给起的名字，具体意思就是多个属性联合在一起来实现某个功能，意会吧）情况的方便之处，在这里提醒一下大家，请尽量使用同一个PropertyChangedCallback来处理属性“联动”问题，否则可能会因为属性赋值先后问题，而导致出现各种“值”不一致的bug

4、{TemplateBinding}绑定方式实现自定义控件

　　用UserControl来制作自定义控件是一个很方便的做法，但是用来制作一些简单或者功能单一的那些最基本的自定义控件时，就显得有点大材小用了，同时UserControl也带来了许多多余的开销，这个时候就可以用另外一种方式来编写这样的控件了，我们可以通过看一下Control4的实现方式，来了解一下

Generic.xaml

<ResourceDictionary  ="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  ="http://schemas.microsoft.com/winfx/2006/xaml"  ="using:Controls">  <Style TargetType="controls:Control4">    <Setter Property="Template">      <Setter.Value>        <ControlTemplate TargetType="controls:Control4">          <Grid>            <TextBlock x:Name="txt" Text="{TemplateBinding Text}"></TextBlock>          </Grid>        </ControlTemplate>      </Setter.Value>    </Setter>  </Style></ResourceDictionary>

Control4.cs

using Windows.UI.Xaml;using Windows.UI.Xaml.Controls;namespace Controls{  public class Control4 : Control  {    TextBlock txt;    public Control4()    {      DefaultStyleKey = typeof(Control4);    }    //public string Text { set; get; }    public string Text    {      get { return (string)GetValue(TextProperty); }      set { SetValue(TextProperty, value); }    }    // Using a DependencyProperty as the backing store for Text. This enables animation, styling, binding, etc...    public static readonly DependencyProperty TextProperty =      DependencyProperty.Register("Text", typeof(string), typeof(Control4), new PropertyMetadata(""));    protected override void OnApplyTemplate()    {      base.OnApplyTemplate();      txt = GetTemplateChild("txt") as TextBlock;    }  }}

这种实现方式有几个特点：

a）Generic.xaml文件要放在主项目的根目录下的一个叫做“Themes”的文件夹下，如果没有“Themes”文件夹，可以自己创建一个

b）构造函数里不能缺少DefaultStyleKey = typeof(Control4)

c）您需要对控件的生命周期有一定的了解，因为在不同的时期txt有可能为null

d）所有的绑定方式都是TemplateBinding，当然你也可以用txt.Text=Text来赋值，但是在这之前最好能确定txt不为空

一般在重写控件时使用的比较多例如重写Button、ListView等，您可以到系统的“C:\Program Files (x86)\Windows Kits\10\DesignTime\CommonConfiguration\Neutral\UAP\{版本号比如 10.0.10586.0}\Generic\generic.xaml”里找到这些控件的样式，可以根据视觉需求对控件样式做一些修改，也可以增加一些自定义的功能

5、比较一下

把这5个控件放到一起比较一下

MainPage.xaml

<Page  x:Class="Controls.MainPage"  ="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  ="http://schemas.microsoft.com/winfx/2006/xaml"  ="using:Controls"  ="http://schemas.microsoft.com/expression/blend/2008"  ="http://schemas.open"  mc:Ignorable="d"  ="using:Controls">  <StackPanel Background="{ThemeResource ApplicationPageBackgroundThemeBrush}" HorizontalAlignment="Center" Margin="40">    <controls:Control1 x:Name="control1" Text="这是控件1"></controls:Control1>    <controls:Control2 x:Name="control2" Text="这是控件2"></controls:Control2>    <controls:Control3 x:Name="control3" Text="这是控件3"></controls:Control3>    <controls:Control4 x:Name="control4" Text="这是控件4"></controls:Control4>    <controls:Control5 x:Name="control5" Text="这是控件5"></controls:Control5>    <TextBox Name="txt"></TextBox>    <Button Click="Button_Click">update</Button>  </StackPanel></Page>

MainPage.xaml.cs

using Windows.UI.Xaml;using Windows.UI.Xaml.Controls;// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409namespace Controls{  /// <summary>  /// An empty page that can be used on its own or navigated to within a Frame.  /// </summary>  public sealed partial class MainPage : Page  {    public MainPage()    {      this.InitializeComponent();    }    private void Button_Click(object sender, RoutedEventArgs e)    {      control1.Text = txt.Text;      control2.Text = txt.Text;      control3.Text = txt.Text;      control4.Text = txt.Text;      control5.Text = txt.Text;    }  }}

运行结果

看上去这些控件都没有问题，但是如果我们在TextBox中输入内容，然后update一下，再看一下结果

　　我们发现Control1和Control3的值没有更新，问题到底出在哪呢？仔细检查一下会发现这俩个控件的Text属性是普通属性（public string Text { set; set; }），依赖属性是有通知属性变更的能力的，而普通属性是不具备这个能力的，所以我们需要控件继承INotifyPropertyChanged接口，于是我们将Control1.xaml.cs作如下变更，Control3也如Control1一样

using System.ComponentModel;using System.Runtime.CompilerServices;using Windows.UI.Xaml.Controls;// The User Control item template is documented at http://go.microsoft.com/fwlink/?LinkId=234236namespace Controls{  public sealed partial class Control1 : UserControl, INotifyPropertyChanged  {    public event PropertyChangedEventHandler PropertyChanged;    public void RaisePropertyChanged([CallerMemberName]string propertyName = null)    {      var handler = PropertyChanged;      if (handler != null)        handler(this, new PropertyChangedEventArgs(propertyName));    }    public Control1()    {      this.InitializeComponent();    }    private string text;    public string Text    {      get      {        return text;      }      set      {        text = value;        RaisePropertyChanged();      }    }  }}

现在我们再来看一下运行结果

Control3是可以了，可是为什么Control1还是不能更新呢，why？让我们来重新看一下Control1的code，原来问题出现在这里

前面我们说过{x:Bind}的默认Mode是OneTime，所以我们需要把它改成OneWay

<UserControl  x:Class="Controls.Control1"  ="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  ="http://schemas.microsoft.com/winfx/2006/xaml"  ="using:Controls"  ="http://schemas.microsoft.com/expression/blend/2008"  ="http://schemas.open"  mc:Ignorable="d"  d:DesignHeight="300"  d:DesignWidth="400">  <Grid>    <TextBlock Text="{x:Bind Text,Mode=OneWay}"></TextBlock>  </Grid></UserControl>

再来不厌其烦地看一下结果

Great！用螺丝钉们经常说的一句话叫“大功告成”。:-D

题外话，给大家出个谜语，猜一猜下面的程序运行结果是多少？

for (var i = 0; i < 10; i++){  await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, async () =>  {    await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>    {      Debug.WriteLine(i);    });  });}

原标题：UWP控件与DataBind

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