I created a new WPF app in Visual Studio and I placed a button using the drag and drop editor but I can't access the button in my .cs file using
MainButton.Content = "Set output to red";
but I get an error
System.NullReferenceException: 'Object reference not set to an instance of an object.'
MainButton was null while running the application.
The drag and drop editor generated this xaml file
<Window x:Class="WpfApp1.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:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfApp1"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Grid>
<Border HorizontalAlignment="Center" VerticalAlignment="Center" BorderBrush="Black" BorderThickness="3">
<TextBlock x:Name="Output" Background="Transparent" TextAlignment="Center" TextWrapping="Wrap" Text="Output" Height="88" Width="264"/>
</Border>
<RadioButton x:Name="Option1" Content="Red Pill" HorizontalAlignment="Left" Margin="135,75,0,0" VerticalAlignment="Top" Checked="RadioButton_Checked" IsChecked="True"/>
<RadioButton x:Name="Option2" Content="Blue Pill" HorizontalAlignment="Left" Margin="536,72,0,0" VerticalAlignment="Top" Checked="RadioButton_Checked_1"/>
<Button x:Name="MainButton" Content="Set output to red" HorizontalAlignment="Left" Margin="279,100,0,0" VerticalAlignment="Top" Width="213" Height="41" Click="MainButton_Click"/>
</Grid>
</Window>
Here's the .cs file
using System.Windows;
using System.Windows.Media;
namespace WpfApp1
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
private void MainButton_Click(object sender, RoutedEventArgs e)
{
if ((bool)Option1.IsChecked)
{
Output.Background = Brushes.Crimson;
}
else
{
Option2.IsChecked = true;
Output.Background = Brushes.DodgerBlue;
}
}
private void RadioButton_Checked(object sender, RoutedEventArgs e)
{
MainButton.Content = "Set output to red";
}
private void RadioButton_Checked_1(object sender, RoutedEventArgs e)
{
MainButton.Content = "Set output to blue";
}
}
}
I can access other things in the UI just fine like radio buttons and text blocks but not the button. Why could this be happening?
During the initialization phase, some variables are going to be null since it hasn't been reached in the call order. RadioButton_Checked is called through event before the button is constructed since it contains the Checked property.
A quick and easy fix is as follows: Check for null in your event calls.
private void RadioButton_Checked (object sender, RoutedEventArgs e)
{
if(MainButton != null)
MainButton.Content = "Set output to red";
}
private void RadioButton_Checked_1 (object sender, RoutedEventArgs e)
{
if (MainButton != null)
MainButton.Content = "Set output to blue";
}
Of course, there are better ways to handle this. You could set checked on a separate event, Initialized, which will handle it much cleaner.
I'm using GalaSoft.MvvmLight.Messaging for communication between classes.
From my ViewModel I'm asking for an object of type view to use it as the content of my DialogHost ( part of the MaterialDesign Framework ):
ViewModel:
Messenger.Default.Send(new NotificationMessage("dialogFormOpenStaple"));
-
private void DialogReceived(string msg, object param)
{
if (msg == "dialogFormOpenStaple")
{
this.dialogContent = param;
this.isDialogOpen = true;
}
}
View
private void NotificationMessageReceived(string msg)
{
if (msg == "dialogFormOpenStaple")
{
object content = new dialogEditMode();
Messenger.Default.Send(new NotificationMessage<object>(content, "dialogFormOpenStaple"));
}
}
All this is working fine. In my XAML itself I got some button bindings to RelayCommands.
<UserControl x:Class="kati2._0.production.dialogEditMode"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:kati2._0.production"
mc:Ignorable="d"
>
[...]
<Button Margin="8 0 0 0" Style="{DynamicResource MaterialDesignFlatButton}" Foreground="#FF757476" IsDefault="True" Command="{Binding dialogOpenStapleNo}">No</Button>
[...]
</UserControl>
Those RelayCommands are defined in my ViewModel. When I open die Dialog for the first time and click on the button it's working fine. If I try it a second time the dialog also opens up but the click event is not getting triggered.
I have a simple ContentDialog with ContentDialog.XAML:
<ContentDialog x:Class="SampleApp.Dialogs"
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="using:SampleApp.Dialog"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
PrimaryButtonClick="OkClick"
PrimaryButtonText="OK"
SecondaryButtonText="Cancel"
SecondaryButtonClick="CancelClick"
mc:Ignorable="d">
<StackPanel>
<TextBox
Text="{x:Bind NameOne, Mode=TwoWay}" />
<TextBox Text="{x:Bind NameTwo, Mode=TwoWay}" />
</StackPanel>
In the code-behind:
private void OkClick(ContentDialog sender, ContentDialogButtonClickEventArgs args)
{
this.Hide();
}
When I want to initalize this Dialog by:
Dialog dialog = new Dialog();
var result = await dialog.ShowAsync();
The resultis always of type ContentDialogResult.None. Even if I click "Ok" or "Cancel", but it should be at least ContentDialogResult.Primary when I click "Ok". It this an expected behavior?
The issue was the PrimaryButtonClick="OkClick" , OkClick overriding the default action (which is hide) and therefore the result is always None.
Removing this solved the problem.
private void OkClick(object sender, RoutedEventArgs e)
{
this.Result = MyResult.Yes;
// Close the dialog
dialog.Hide();
}
I'm learning WPF (moving from Procedural PHP) and have written the following to navigate from 'MainWindow' to 'Page1', where there are no errors with the login credentials, but the local variable 'nav' is always null (hence displaying an error message):
namespace YM_POS_20160229_0949
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
public void ClickLoginSubmitButton(object sender, RoutedEventArgs e)
{
// Dictionary object is c# equivalent of PHP's 'array["key"] = "value"'
Dictionary<string, string> errMsg = new Dictionary<string, string>();
// declare variables
string varUserName;
string varUserPass;
// define the variables whilst trimming the values passed
varUserName = LoginUsername.Text.Trim();
varUserPass = LoginPassword.Password.Trim();
// ensure something has been submitted & perform validation on the values submitted
// if there are no errors, navigate to the users dashboard (aka Page1)
NavigationService nav = NavigationService.GetNavigationService(new Page1());
// check if the nav variable is populated
if (nav != null)
{
nav.Navigate(nav);
}
else
{
// display an error message to the user advising them an error has occurred and Page1 is not available
MessageBox.Show("An error has occured. unable to proceed to " + nav);
}
}
}
}
Any help greatly appreciated.
Thanks
Newbie Matt
//UI / XAML
<Window x:Class="YM_POS_20160229_0949.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:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:YM_POS_20160229_0949"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<DockPanel>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="123*"/>
<ColumnDefinition Width="394*"/>
</Grid.ColumnDefinitions>
<TextBox x:Name="LoginUsername" HorizontalAlignment="Left" Height="23" Margin="56.649,55,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120" Grid.Column="1"/>
<PasswordBox x:Name="LoginPassword" HorizontalAlignment="Left" Height="23" Margin="56.649,100,0,0" Password="Password" VerticalAlignment="Top" Width="120" Grid.Column="1" />
<Button x:Name="LoginSubmitButton" Content="Submit" HorizontalAlignment="Left" Margin="81.649,172,0,0" VerticalAlignment="Top" Width="75" Click="ClickLoginSubmitButton" Grid.Column="1"/>
</Grid>
</DockPanel>
</Window>
I am attempting to create a program in which the User can create multiple profiles. These profiles can be accessed via buttons that appear as each profile is completed.
My problem:
I have no clue how to make the created buttons persist after the program is exited(I need to save the buttons?)
Visually, this is program's process: 1) Enter your information, click continue 2) View a display page of what you entered, click done. 3) This adds a button to the final window, the button of course takes you to 4) Your profile you just created.
After this, the program ends and nothing is saved. I'm fairly new to c# and am quite confused on how to "save" multiple buttons without massively complicating the code. I'm a complete noob to c# and have a little Java experience. Am I going about this correctly? I'm pretty sure its possible but have no idea to go about it.
I will include my code below. I'm working in visual studios 2012. any help would be appreciated!
MainWindow XAML:
<Window x:Class="VendorMain.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Label Content="FirstName" HorizontalAlignment="Left" Margin="63,45,0,0" VerticalAlignment="Top"/>
<Label Content="LastName" HorizontalAlignment="Left" Margin="63,71,0,0" VerticalAlignment="Top"/>
<Label Content="Image" HorizontalAlignment="Left" Margin="63,102,0,0" VerticalAlignment="Top"/>
<Image Name="imgPhoto" Stretch="Fill" Margin="63,133,303,69"></Image>
<Button Name="UploadImageButton" Content="Upload Image" HorizontalAlignment="Left" Margin="130,105,0,0" VerticalAlignment="Top" Width="84" Click="UploadImageButton_Click"/>
<TextBox Name="AssignFirstName" Text="{Binding SettingFirstname}" HorizontalAlignment="Left" Height="23" Margin="130,48,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120" />
<TextBox Name="AssignLastName" Text="{Binding SettingLastName}" HorizontalAlignment="Left" Height="23" Margin="130,75,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
<Button Name="ContinueToDisplayWindow" Content="Continue" HorizontalAlignment="Left" Margin="409,288,0,0" VerticalAlignment="Top" Width="75" Click="ContinueToDisplayWindow_Click" />
</Grid>
MainWindow Code:
namespace VendorMain
{
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
private void UploadImageButton_Click(object sender, RoutedEventArgs e)
{
OpenFileDialog op = new OpenFileDialog();
op.Title = "Select a picture";
op.Filter = "All supported graphics|*.jpg;*.jpeg;*.png|" +
"JPEG (*.jpg;*.jpeg)|*.jpg;*.jpeg|" +
"Portable Network Graphic (*.png)|*.png";
if (op.ShowDialog() == true)
{
imgPhoto.Source = new BitmapImage(new System.Uri(op.FileName));
//SettingImage.Source = imgPhoto.Source;
}
}
private void ContinueToDisplayWindow_Click(object sender, RoutedEventArgs e)
{
DisplayPage displaypg = new DisplayPage();
displaypg.DpFirstName.Content = AssignFirstName.Text;
displaypg.DpLastName.Content = AssignLastName.Text;
displaypg.DpImage.Source = imgPhoto.Source;
displaypg.Show();
}
}
}
DisplayPage XAML:
<Window x:Class="VendorMain.DisplayPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="DisplayPage" Height="300" Width="525">
<Grid>
<Label Name="DpFirstName" Content="{Binding getFirstNamePermenent}" HorizontalAlignment="Left" Margin="86,55,0,0" VerticalAlignment="Top"/>
<Label Name="DpLastName" Content="{Binding getLastNamePermenent}" HorizontalAlignment="Left" Margin="87,80,0,0" VerticalAlignment="Top"/>
<Image Name="DpImage" HorizontalAlignment="Left" Height="100" Margin="94,111,0,0" VerticalAlignment="Top" Width="100"/>
<Button Name="ButtonizeThisProfile_Button" Content="Done" HorizontalAlignment="Left" Margin="420,238,0,0" VerticalAlignment="Top" Width="75" Click="ButtonizeThisProfile_Button_Click"/>
</Grid>
DisplayPage Code:
namespace VendorMain
{
/// <summary>
/// Interaction logic for DisplayPage.xaml
/// </summary>
public partial class DisplayPage : Window
{
public Button bot1;
public DisplayPage()
{
InitializeComponent();
}
private void newBtn_Click(object sender, RoutedEventArgs e)
{
carryToFinalView();
}
private void ButtonizeThisProfile_Button_Click(object sender, RoutedEventArgs e)
{
UserProfiles uPro = new UserProfiles();
System.Windows.Controls.Button newBtn = new Button();
newBtn.Content = "Person1";
newBtn.Name = "NewProfileButtonAccess";
newBtn.Click += new RoutedEventHandler(newBtn_Click);
uPro.ButtonArea.Children.Add(newBtn);
uPro.Show();
}
public void carryToFinalView()
{
DisplayPage displaypg = new DisplayPage();
displaypg.DpFirstName.Content = DpFirstName.Content;
displaypg.DpLastName.Content = DpLastName.Content;
displaypg.DpImage.Source = DpImage.Source;
displaypg.Show();
}
}
}
UserProfile XAML:
<Window x:Class="VendorMain.UserProfiles"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="UserProfiles" Height="300" Width="525">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width=".8*" />
<ColumnDefinition Width="2*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="6*"/>
<RowDefinition Height="11*"/>
</Grid.RowDefinitions>
<Label Content="User Profiles: " HorizontalAlignment="Left" Margin="37,47,0,0" VerticalAlignment="Top"/>
<StackPanel Name="ButtonArea" Grid.Column="2" Grid.Row="2">
</StackPanel>
<Button Name="AddAnotherProfileButton" Content="Button" HorizontalAlignment="Left" Margin="35,146,0,0" Grid.Row="1" VerticalAlignment="Top" Width="75" Click="AddAnotherProfileButton_Click"/>
</Grid>
UserProfile Code:
namespace VendorMain
{
public partial class UserProfiles : Window
{
public UserProfiles()
{
InitializeComponent();
}
private void AddAnotherProfileButton_Click(object sender, RoutedEventArgs e)
{
MainWindow mw = new MainWindow();
mw.Show();
}
}
}
As a self proclaimed 'noob', I fear that you won't receive an answer here. I certainly don't have time to repeatedly come back to answer a whole continuing stream of related questions. I also don't have time to provide you with a complete solution. However, I am happy to provide you with sort of 'pseudo code' to at least point you in the right direction... you will have to do a lot of this yourself.
So first things first, as mentioned in a comment, although it is possible, we don't generally save the UI Button objects, but instead we save the data that relates to the user profiles. Therefore, if you haven't done this already, create a User class that has all of the relevant properties. Implement the INotifyPropertyChanged Interface in it and add the SerializableAttribute to the class definition... this will enable you to save this class type as binary data.
Next, in your UI, don't add each Button in xaml... there's a better way. One way or another, add a collection property of type User or whatever your class is called, and set this as the ItemsSource of a ListBox. The idea here is to add a DataTemplate for your User type which will display each of the User items in the collection as a Button:
<DataTemplate x:Key="UserButtonTemplate" DataType="{x:Type DataTypes:User}">
<Button Text="{Binding Name}" Width="75" Click="AddAnotherProfileButton_Click" />
</DataTemplate>
You can find out more about DataTemplates in the Data Templates article.
Implementing this collection allows you to have and display any number of user profiles in your UI, rather than being restricted by screen size as your original example would be.
Now finally, on to saving the data... this can be achieved relatively simply using the following code:
try
{
using (Stream stream = File.Open("ProfileData.bin", FileMode.Create))
{
BinaryFormatter binaryFormatter = new BinaryFormatter();
binaryFormatter .Serialize(stream, usersList);
}
}
catch { }
One thing to note is that WPF wants us to use the ObservableCollection<T> class when displaying data in the UI, but this class causes problems when serializing data with this method... therefore, you will need to convert your ObservableCollection<T> to a List<T> or similar. However, this can be easily achieved:
List<User> usersList = users.ToList();
You can find out how to de-serialize your data from the C# Serialize List tutorial. You would deserialize (or load the data from the saved file) each time your application starts and re-save the file each time the program closes. You can add an event handler to the Application.Deactivated Event or the Window.Closing which gets called when the application closes, so you can put your code to save the file in there.
Well, I took longer and wrote more than I had expected, so I hope that helps.