Imagine Windows 8.1 Store Apps (82)

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Re-imagine Windows 8.1 Store Apps (82)-binding: DataContextChanged, TargetNullValue, FallbackValue, UpdateSourceTrigger

Author: webabcd


Introduction
Re-imagine binding Windows 8.1 Store Apps

• Events triggered when the DataContext of DataContextChanged-FrameworkElement changes
• TargetNullValue-value to be displayed when the bound data is null
• FallbackValue-the value to be displayed when the binding fails (the return value cannot be returned)
• UpdateSourceTrigger-data update trigger method on the UI

Example
1. Demonstrate the DataContextChanged Application
DataContextChanged. xaml

<Page x: Class = "Windows81.Binding. dataContextChanged "xmlns =" http://schemas.microsoft.com/winfx/2006/xaml/presentation "xmlns: x =" http://schemas.microsoft.com/winfx/2006/xaml "xmlns: local =" using: Windows81.Binding "xmlns: d =" http://schemas.microsoft.com/expression/blend/2008 "xmlns: mc =" http://schemas.openxmlformats.org/markup-compatibility/2006 "mc: ignorable = "d"> <Grid Background = "Transparent"> <StackPanel Margin = "120 0 0 0"> <TextBlock Name = "lblMsg" FontSize = "14.667"/> <button x: name = "btnChange" Content = "change data context" Click = "btnChange_Click" Margin = "0 10 0 0"/> <ListBox x: name = "listBox" ItemsSource = "{Binding}" DataContextChanged = "listBox_DataContextChanged" Margin = "0 10 0 0"/> </StackPanel> </Grid> </Page>

DataContextChanged. xaml. cs

/** Events triggered when the DataContext of DataContextChanged-FrameworkElement changes *** for details about the binding basics, see :* http://www.cnblogs.com/webabcd/archive/2013/08/19/3267115.html * http://www.cnblogs.com/webabcd/archive/2013/08/22/3274099.html * http://www.cnblogs.com/webabcd/archive/2013/08/26/3281822.html * http://www.cnblogs.com/webabcd/archive/2013/08/29/3288304.html */Using System; using System. collections. generic; using Windows. UI. xaml; using Windows. UI. xaml. controls; namespace Windows81.Binding {public sealed partial class DataContextChanged: Page {public DataContextChanged () {this. initializeComponent (); this. loaded + = new RoutedEventHandler (DataContextChanged_Loaded);} void DataContextChanged_Loaded (object sender, RoutedEventArgs e) {// specify the data context listBox. dataContext = new List <string> {"a", "B", "c" };} private void btnChange_Click (object sender, RoutedEventArgs e) {// modify the data context listBox. dataContext = new List <string> {"a", "B", new Random (). next (0, 1000 ). toString (). padLeft (3, '0')};} private void listBox_DataContextChanged (FrameworkElement sender, DataContextChangedEventArgs args) {/** FrameworkElement. dataContextChanged-events triggered after the data context changes * // lblMsg after the data context changes. text = "Data Source changed:" + DateTime. now. toString ("hh: mm: ss ");}}}

2. demonstrate the application of TargetNullValue and FallbackValue
TargetNullValueFallbackValue. xaml

<Page x: Class = "Windows81.Binding. targetNullValueFallbackValue "xmlns =" http://schemas.microsoft.com/winfx/2006/xaml/presentation "xmlns: x =" http://schemas.microsoft.com/winfx/2006/xaml "xmlns: local =" using: Windows81.Binding "xmlns: d =" http://schemas.microsoft.com/expression/blend/2008 "xmlns: mc =" http://schemas.openxmlformats.org/markup-compatibility/2006 "mc: ignorable = "d"> <Grid Background = "Transparent "> <StackPanel Name =" stackPanel "Margin =" 120 0 0 0 "> <! -- FallbackValue-value to be displayed when Binding fails (cannot return value) --> <TextBlock FontSize = "14.667" Text = "{Binding Path = xxx, fallbackValue = 'default value when binding fails '} "/> <! -- TargetNullValue-the value to be displayed when the bound data is null --> <TextBlock FontSize = "14.667" Text = "{Binding Path = Name, targetNullValue = 'Return value of binding null'} "Margin =" 0 10 0 0 "/> </StackPanel> </Grid> </Page>

TargetNullValueFallbackValue. xaml. cs

/** TargetNullValue-the value to be displayed when the bound data is null * FallbackValue-when the binding fails (the return value cannot be returned) the value to be displayed when *** about binding basics see * http://www.cnblogs.com/webabcd/archive/2013/08/19/3267115.html * http://www.cnblogs.com/webabcd/archive/2013/08/22/3274099.html * http://www.cnblogs.com/webabcd/archive/2013/08/26/3281822.html * http://www.cnblogs.com/webabcd/archive/2013/08/29/3288304.html */using Windows. UI. xaml. controls; using Windows. UI. xaml. navigation; namespace Windows81.Binding {public sealed partial class TargetNullValueFallbackValue: Page {public TargetNullValueFallbackValue () {this. initializeComponent ();} protected override void OnNavigatedTo (NavigationEventArgs e) {stackPanel. dataContext = new TargetNullValueTest {Name = null };}} public sealed class TargetNullValueTest {public string Name {get; set ;}}}

3. demonstrate the application of UpdateSourceTrigger
UpdateSourceTrigger. xaml

<Page x: Class = "Windows81.Binding. UpdateSourceTrigger" xmlns =" http://schemas.microsoft.com/winfx/2006/xaml /Presentation "xmlns: x =" http://schemas.microsoft.com/winfx/2006/xaml "Xmlns: local =" using: Windows81.Binding "xmlns: d =" http://schemas.microsoft.com/expression/blend/2008 "Xmlns: mc =" http://schemas.openxmlformats.org/markup-compatibility/2006 "Mc: ignorable = "d"> <Grid Background = "Transparent"> <StackPanel Name = "stackPanel" Margin = "120 0 0 0"> <TextBlock Name = "lblMsg"/> <! -- UpdateSourceTrigger-Method of triggering data update on UI Default-triggering PropertyChanged when the focus is lost-triggering Explicit when the attribute value changes-BindingExpression is required. updateSource () display trigger --> <TextBox Text = "{Binding Text, Mode = TwoWay, ElementName = lblMsg, updateSourceTrigger = Default} "Margin =" 0 10 0 0 "/> <TextBox Text =" {Binding Text, Mode = TwoWay, ElementName = lblMsg, updateSourceTrigger = PropertyChanged} "Margin =" 0 10 0 0 "/> <TextBox Name =" txtExplicit "Text =" {Binding Text, Mode = TwoWay, ElementName = lblMsg, updateSourceTrigger = Explicit} "Margin =" 0 10 0 0 "/> <Button Name =" btnBinding "Content =" display trigger Update "Click =" btnBinding_Click "Margin =" 0 10 0 0 "/> </StackPanel> </Grid> </Page>

UpdateSourceTrigger. xaml. cs

/** Trigger method of UpdateSourceTrigger-data update on UI * Default-trigger * PropertyChanged-trigger * Explicit after the property value changes-BindingExpression is required. updateSource () displays trigger *** for the basics of binding, see * http://www.cnblogs.com/webabcd/archive/2013/08/19/3267115.html * http://www.cnblogs.com/webabcd/archive/2013/08/22/3274099.html * http://www.cnblogs.com/webabcd/archive/2013/08/26/3281822.html * http://www.cnblogs.com/webabcd/archive/2013/08/29/3288304.html */using Windows. UI. xaml; using Windows. UI. xaml. controls; using Windows. UI. xaml. data; namespace Windows81.Binding {public sealed partial class UpdateSourceTrigger: Page {public UpdateSourceTrigger () {this. initializeComponent ();} private void btnBinding_Click (object sender, RoutedEventArgs e) {// display the data update BindingExpression that triggers txtExplicit. be = txtExplicit. getBindingExpression (TextBox. textProperty); be. updateSource ();}}}

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