Develop Reference

Xamarin.Forms (iOS) - How to change the text of the SearchBar "Cancel" button?

We are internationalizing a mobile app my team is developing, and I noticed the "Cancel" button in the SearchBar is not translating (everything else is translating just fine) - it always says "Cancel" in English no matter what language I change the iPad simulator to. If I can set the text myself, then I can ensure it's internationalized properly. So...
How do I change the "Cancel" button text on a Xamarin.Forms SearchBar? I've tried a custom renderer, but am having difficulty targeting the Cancel button subview. This answer seems to do a great job of explaining how to do that in Objective C, but I'm having trouble translating it into C# within the Xamarin.Forms framework.

Create a new custom renderer for iOS. Something like CustomSearchBarRenderer and subclass the Xamarin's original SearchBarRenderer
public class CustomSearchBarRenderer : SearchBarRenderer { }
I'd probably try to override OnElementChanged method and set the custom title after the base class has done all the work. Like this:
protected override void OnElementChanged(ElementChangedEventArgs<SearchBar> e)
{
base.OnElementChanged(e);
var cancelButton = Control.FindDescendantView<UIButton>();
cancelButton.Title = "Whatever";
}
Edit: Please be aware that the cancelButton might get recreated at some point so you might have to set the title at some other point too. However, this should be a good starting point.
You can also take a look at the current SearchBarRenderer implementation here.

I combined the answers and set the button text on each event which is needed. I also fixed the showing and hiding of the cancel button (see here):
using FestivalHolledauApp.iOS;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
using System.Linq;
[assembly: ExportRenderer(typeof(SearchBar), typeof(CustomSearchBarRenderer))]
namespace FestivalHolledauApp.iOS
{
public class CustomSearchBarRenderer : SearchBarRenderer
{
protected override void OnElementChanged(ElementChangedEventArgs<SearchBar> e)
{
base.OnElementChanged(e);
// Fixing Cancel button
if (e.NewElement != null)
{
this.Control.TextChanged += (s, ea) =>
{
this.Control.ShowsCancelButton = true;
SetCancelButtonText();
};
this.Control.OnEditingStarted += (s, ea) => //when control receives focus
{
this.Control.ShowsCancelButton = true;
SetCancelButtonText();
};
this.Control.OnEditingStopped += (s, ea) => //when control looses focus
{
this.Control.ShowsCancelButton = false;
};
}
}
private void SetCancelButtonText()
{
var cancelButton = Control.Descendants().OfType<UIButton>().FirstOrDefault();
if (cancelButton != null)
{
cancelButton.SetTitle("Schließen", UIControlState.Normal);
}
}
}
}

I've come over the same issue with ...
the "Cancel" button in a UISearchBar
the "Back" button to prior pages without title
context menu actions like "Cut", "Copy" and "Paste"
the "Done" buttons on date pickers and multiline editors
Everything else I got localized with resource based localization.
There are a lot of hacks out there finding the native buttons and setting texts manually but I knew this was not the way it was meant to be. So I digged deeper and found the following excellent article from Gerald Versluis:
https://blog.verslu.is/xamarin/xamarin-forms-xamarin/localization-default-ios-controls/
For me, this just meant to add the following block to my Info.plist:
<key>CFBundleLocalizations</key>
<array>
<string>en</string>
<string>de</string>
</array>
With this, iOS automatically translated all the UI elements for the current system culture (without adding these text to any resource files).

How to override System.Windows.Forms label background color in C#?

I'm trying to write a class to override ALL my label backgrounds in my entire project without changing their definition in designer.cs files.
I mean I could simply change this.label1 = new System.Windows.Forms.Label(); to something like this.label1 = new myLabel(); but I don't want to do this.
This is my label.cs
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace T1
{
class Label:System.Windows.Forms.Label
{
public override Color BackColor
{
get
{
return Color.DarkRed;
}
set
{
base.BackColor = value;
}
}
}
}
I tried to call my namespace System.Windows.Forms in hope to override it's current label color property, but I couldn't get anywhere so far.
Any help would be appreciated.
All the Best.

First, let me start by saying that I think it really sounds like you would be better off by replacing references with your overridden label as you have mentioned (maybe not by editing the designer.cs but by replacing the controls)
But in further to my comment, you can create your own form to override all your forms that require its controls adjusted like this and then inherit from that form
class MyMiddleFormClass : Form
{
public MyMiddleFormClass()
{
this.OnLoad += OnLoadHandler;
}
private void OnLoadHandler(object o, EventArgs e)
{
foreach(var lbl in this.Controls.OfType<Label>())
lbl.BackColor = Color.DarkRed;
}
}
Note: I haven't tested this code and may require extra work if you need to use the OnLoad event yourself.
Again, you would benefit a lot more by spending the time now refactoring your controls instead of doing this.

Aforge.net Camera Capture & Save image to directory

everyone. I have been stuck here dealing with this bugs for days, but I still couldn't figure it out.
My guess: I think my code has some problem as I did not dispose the object properly after using it, (I'm not very familiar with these concepts of releasing resources, threading) .
I got these code by taking reference of what people did on youtube, but despite me doing exactly the same thing, my code didn't work out nicely.
SITUATION:
I have two picture boxes, left one can take video of me, right one take the snapshot, if you press button1 , you will start the video, clone_button will copy a image i.e. take a snapshot, and save_image should save it to the path reference, however, i get a generic error occured in GDI+ again and again while I'm trying to save it. Also, my debugger seemed to get crazy (i.e. failed to terminate the vshost.exe ) once I ran this program, I have to restart the computer to get my code running again, which is bleak and frustrating.
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Drawing.Imaging;
//AForge.Video dll
using AForge.Video;
using AForge.Video.DirectShow;
using AForge.Imaging;
using AForge.Imaging.Filters;
using AForge;
namespace WebCameraCapture
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private FilterInfoCollection CaptureDevice; // list of webcam
private VideoCaptureDevice FinalFrame;
private void Form1_Load(object sender, EventArgs e)
{
CaptureDevice = new FilterInfoCollection(FilterCategory.VideoInputDevice);//constructor
foreach (FilterInfo Device in CaptureDevice)
{
comboBox1.Items.Add(Device.Name);
}
comboBox1.SelectedIndex = 0; // default
FinalFrame = new VideoCaptureDevice();
}
private void button1_Click(object sender, EventArgs e)
{
FinalFrame = new VideoCaptureDevice(CaptureDevice[comboBox1.SelectedIndex].MonikerString);// specified web cam and its filter moniker string
FinalFrame.NewFrame += new NewFrameEventHandler(FinalFrame_NewFrame);// click button event is fired,
FinalFrame.Start();
}
void FinalFrame_NewFrame(object sender, NewFrameEventArgs eventArgs) // must be void so that it can be accessed everywhere.
// New Frame Event Args is an constructor of a class
{
pictureBox1.Image = (Bitmap)eventArgs.Frame.Clone();// clone the bitmap
}
private void From1_CLosing(object sender, EventArgs e)
{
if (FinalFrame.IsRunning==true) FinalFrame.Stop();
}
private void save_Click(object sender, EventArgs e)
{
if (pictureBox2.Image != null)
{
Bitmap varBmp = new Bitmap(pictureBox2.Image);
Bitmap newBitmap = new Bitmap(varBmp);
varBmp.Dispose();
varBmp = null;
varBmp.Save(#"C:\a.png", ImageFormat.Png);
}
else
{ MessageBox.Show("null exception"); }
}
private void clone_Click(object sender, EventArgs e)
{
pictureBox2.Image = (Bitmap)pictureBox1.Image.Clone();
}
}
}
Any AForge.net user can just PRESS the LINK below and try it out. Thanks!
SAMPLE

After having a look at your code, to me it appears that you are disposing of your image right before you save it. Meaning that your program can't save the image, because it doesn't exist anymore. Actually it reads that you've essentially removed the captured image twice, once on dispose, the second when you set it as null.
So if you move the two code segments after the save, it should be working. Granted without using a dialog box to change the name of the file, you'll surely receive an error unless you remove that file after each time it has been created.
private void save_Click(object sender, EventArgs e)
{
if (pictureBox2.Image != null)
{
//Save First
Bitmap varBmp = new Bitmap(pictureBox2.Image);
Bitmap newBitmap = new Bitmap(varBmp);
varBmp.Save(#"C:\a.png", ImageFormat.Png);
//Now Dispose to free the memory
varBmp.Dispose();
varBmp = null;
}
else
{ MessageBox.Show("null exception"); }
}
If you open the task manager, you can watch how much memory your program is soaking up.
Disposing of the memory after you're done using it, gives it back to the system.
You don't have a dispose inside your FinalFrame_NewFrame thread, so when the camera is reading images,
you should see the memory usage continue to climb until you stop the program.
I've added dispose to my thread, putting the memory usage under control, but now I'm debugging my image saves. Because I'm disposing, I can't save the image lol. My program ends up trying to save a null image file and throws the appropriate error.
I'm using a 2nd picurebox just as you are, but using for example, pbox2.image = pbox1.image, doesn't copy the data, it copies the memory location with the image data, so when I dispose pbox1 to free memory, the image data disappears with the memory location.

So, I had the same issue, and it was resolved one, by moving the dispose method, and two, I had to change the path, it didnt want to save to C:, so I put it on my desktop, you may not have had this issue if you were running as admin but I did so for anyone else who sees this, dont save to the root of C:.

nullReferenceException when i try to play a sound effect?

I'm making a soundboard with sound effects and I'm getting :
"A first chance exception of type 'System.NullReferenceException'"
when building after 'UI Task' (Managed):
Loaded 'Microsoft.Xna.Framework.dll'
I did have it working but after changes (overwrote previous version) I have been getting this error and I'm stuck. Java is my first language and with C# I'm a beginner. I have spent countless hours looking for a solution.
The nullReferenceException is coming from loadsound(), I think! I have the sound files(.wav) in a folder called resources and build action:resources and copy to output:do not copy(have tried all options here). Also in references a reference was made to Microsoft.Xna.Framework
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Resources;
using System.Windows.Shapes;
using Microsoft.Phone.Controls;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Media;
namespace Craggy_Island
{
public partial class MainPage : PhoneApplicationPage
{
// The Resources to play
private SoundEffect drink;//(plus 23 more effects)
// Flag that indicates if we need to resume Zune playback upon exiting.
bool resumeMediaPlayerAfterDone = false;
// Constructor
public MainPage()
{
InitializeComponent();
// Timer to simulate the XNA game loop (SoundEffect class is from the XNA Framework)
GameTimer gameTimer = new GameTimer();
gameTimer.UpdateInterval = TimeSpan.FromMilliseconds(33);
// Call FrameworkDispatcher.Update to update the XNA Framework internals.
gameTimer.Update += delegate { try { FrameworkDispatcher.Update(); } catch { } };
// Start the GameTimer running.
gameTimer.Start();
// Prime the pump or we'll get an exception.
FrameworkDispatcher.Update();
//LoadSound("Resources/drink.wav", out drink);
// Create and load SoundEffect objects.
LoadSound("Resources/drink.wav", out drink);
}
private void LoadSound(String SoundFilePath, out SoundEffect Sound)
{
// For error checking, assume we'll fail to load the file.
Sound = null;
try
{
// Holds informations about a file stream.
StreamResourceInfo SoundFileInfo = App.GetResourceStream(new Uri(SoundFilePath, UriKind.Relative));
// Create the SoundEffect from the Stream
Sound = SoundEffect.FromStream(SoundFileInfo.Stream);
}
catch (NullReferenceException)
{
// Display an error message
MessageBox.Show("Couldn't load sound " + SoundFilePath);
}
}
private void button_Click(object sender, RoutedEventArgs e)
{
Button Current = sender as Button;
try
{
if (Current.Equals(button1))
drink.Play();//(other buttons here for other sound effects)
}
catch (NullReferenceException)
{
MessageBox.Show("Can't play, sound file problem.");
}
}
#region Zune Pause/Resume
private void ZunePause()
{
// Please see the MainPage() constructor above where the GameTimer object is created.
// This enables the use of the XNA framework MediaPlayer class by pumping the XNA FrameworkDispatcher.
// Pause the Zune player if it is already playing music.
if (!MediaPlayer.GameHasControl)
{
MediaPlayer.Pause();
resumeMediaPlayerAfterDone = true;
}
}
private void ZuneResume()
{
// If Zune was playing music, resume playback
if (resumeMediaPlayerAfterDone)
{
MediaPlayer.Resume();
}
}
#endregion Zune Pause/Resume
}
}

Scrap my original answer unless you're using XNA for game development on Windows/Xbox. (Original poster is using it for the Zune.)
Regarding the WAV file:
First problem is that you need to set Copy to Output Directory to Copy if newer. (You could use Always, but that would be unnecessary.)
Second problem is that its type needs to be set to Content.

You are taking the hard approach. Look into ContentManager (accessible as this.Content from within the Game instance). You can use Content.Load<T>(string) to access your audio file, but you'll need to put the audio file in the content project. Don't change its type: leave it at the default. Even it's not a resource, leave it be. It will be compiled into a different format. Also, omit the file extension from the parameter passed to Content.Load<>.

You are starting the game before you are loading the sound:
gameTimer.Start();
FrameworkDispatcher.Update();
LoadSound("Resources/drink.wav", out drink);

I had almost the same problem. Finally I got it accidently as follows:
StreamResourceInfo streaminfo = Application.GetResourceStream(new Uri("project_name;component/folder_name/Sound3.wav", UriKind.RelativeOrAbsolute));
SoundEffect effect1 = SoundEffect.FromStream(streaminfo.Stream);
effect1.Play();
AND:
the Property "Build Action" of the .wav file must be setted to "Resource" and the Porperty "Copy to Output Directory" should be setted to "Copy if newer"
By the way, I´m working with Silverlight5.

c# flickering Listview on update

I have a list view that is periodically updated (every 60 seconds). It was anoying to me that i would get a flicker every time it up dated. The method being used was to clear all the items and then recreate them. I decided to instead of clearing the items I would just write directly to the cell with the new text. Is this a better approach or does anyone have a better solution.

The ListView control has a flicker issue. The problem appears to be that the control's Update overload is improperly implemented such that it acts like a Refresh. An Update should cause the control to redraw only its invalid regions whereas a Refresh redraws the control’s entire client area. So if you were to change, say, the background color of one item in the list then only that particular item should need to be repainted. Unfortunately, the ListView control seems to be of a different opinion and wants to repaint its entire surface whenever you mess with a single item… even if the item is not currently being displayed. So, anyways, you can easily suppress the flicker by rolling your own as follows:
class ListViewNF : System.Windows.Forms.ListView
{
public ListViewNF()
{
//Activate double buffering
this.SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.AllPaintingInWmPaint, true);
//Enable the OnNotifyMessage event so we get a chance to filter out
// Windows messages before they get to the form's WndProc
this.SetStyle(ControlStyles.EnableNotifyMessage, true);
}
protected override void OnNotifyMessage(Message m)
{
//Filter out the WM_ERASEBKGND message
if(m.Msg != 0x14)
{
base.OnNotifyMessage(m);
}
}
}
From: Geekswithblogs.net

In addition to the other replies, many controls have a [Begin|End]Update() method that you can use to reduce flickering when editing the contents - for example:
listView.BeginUpdate();
try {
// listView.Items... (lots of editing)
} finally {
listView.EndUpdate();
}

Here is my quick fix for a C# implementation that does not require subclassing the list views etc.
Uses reflection to set the DoubleBuffered Property to true in the forms constructor.
lvMessages
.GetType()
.GetProperty("DoubleBuffered", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)
.SetValue(lvMessages, true, null);
Update for 2021:
I got pinged on this old post with a comment and I would write this code differently now. Below is an extension method that will add a new method to a ListView to be able to set the double buffered property to true/false as required. This will then extend all list views and make it easier to call as reqired.
/// <summary>
/// Extension methods for List Views
/// </summary>
public static class ListViewExtensions
{
/// <summary>
/// Sets the double buffered property of a list view to the specified value
/// </summary>
/// <param name="listView">The List view</param>
/// <param name="doubleBuffered">Double Buffered or not</param>
public static void SetDoubleBuffered(this System.Windows.Forms.ListView listView, bool doubleBuffered = true)
{
listView
.GetType()
.GetProperty("DoubleBuffered", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)
.SetValue(listView, doubleBuffered, null);
}
}

If this can help, the following component solved my ListView flickering issues with .NET 3.5
[ToolboxItem(true)]
[ToolboxBitmap(typeof(ListView))]
public class ListViewDoubleBuffered : ListView
{
public ListViewDoubleBuffered()
{
this.DoubleBuffered = true;
}
}
I use it in conjonction with .BeginUpdate() and .EndUpdate() methods where I do ListView.Items manipulation.
I don't understand why this property is a protected one...even in the .NET 4.5 (maybe a security issue)

Yes, make it double buffered. It will reduce the flicker ;) http://msdn.microsoft.com/en-us/library/system.windows.forms.listview.doublebuffered.aspx

Excellent question and Stormenent's answer was spot on. Here's a C++ port of his code for anyone else who might be tackling C++/CLI implementations.
#pragma once
#include "Windows.h" // For WM_ERASEBKGND
using namespace System;
using namespace System::Windows::Forms;
using namespace System::Data;
using namespace System::Drawing;
public ref class FlickerFreeListView : public ListView
{
public:
FlickerFreeListView()
{
//Activate double buffering
SetStyle(ControlStyles::OptimizedDoubleBuffer | ControlStyles::AllPaintingInWmPaint, true);
//Enable the OnNotifyMessage event so we get a chance to filter out
// Windows messages before they get to the form's WndProc
SetStyle(ControlStyles::EnableNotifyMessage, true);
}
protected:
virtual void OnNotifyMessage(Message m) override
{
//Filter out the WM_ERASEBKGND message
if(m.Msg != WM_ERASEBKGND)
{
ListView::OnNotifyMessage(m);
}
}
};

You can use the following extension class to set the DoubleBuffered property to true:
using System.Reflection;
public static class ListViewExtensions
{
public static void SetDoubleBuffered(this ListView listView, bool value)
{
listView.GetType()
.GetProperty("DoubleBuffered", BindingFlags.Instance | BindingFlags.NonPublic)
.SetValue(listView, value);
}
}

The simplest Solution would probably be using
listView.Items.AddRange(listViewItems.ToArray());
instead of
foreach (ListViewItem listViewItem in listViewItems)
{
listView.Items.Add(listViewItem);
}
This works way better.

Simple solution
yourlistview.BeginUpdate()
//Do your update of adding and removing item from the list
yourlistview.EndUpdate()

I know this is an extremely old question and answer. However, this is the top result when searching for "C++/cli listview flicker" - despite the fact that this isn't even talking about C++. So here's the C++ version of this:
I put this in the header file for my main form, you can choose to put it elsewhere...
static void DoubleBuffer(Control^ control, bool enable) {
System::Reflection::PropertyInfo^ info = control->GetType()->
GetProperty("DoubleBuffered", System::Reflection::BindingFlags::Instance
| System::Reflection::BindingFlags::NonPublic);
info->SetValue(control, enable, nullptr);
}
If you happen to land here looking for a similar answer for managed C++, that works for me. :)

This worked best for me.
Since you are editing the cell directly, the best solution in your case would be to simply refresh/reload that particular cell/row instead of the entire table.
You could use the RedrawItems(...) method that basically repaints only the specified range of items/rows of the listview.
public void RedrawItems(int startIndex, int endIndex, bool invalidateOnly);
Reference
This totally got rid of the full listview flicker for me.
Only the relevant item/record flickers while getting updated.
Cheers!

Try setting the double buffered property in true.
Also you could use:
this.SuspendLayout();
//update control
this.ResumeLayout(False);
this.PerformLayout();

In Winrt Windows phone 8.1 you can set the following code to fix this issue.
<ListView.ItemContainerTransitions>
<TransitionCollection/>
</ListView.ItemContainerTransitions>

For what it's worth, in my case, I simply had to add a call to
Application.EnableVisualStyles()
before running the application, like this:
private static void Main()
{
Application.EnableVisualStyles();
Application.Run(new Form1());
}
Otherwise, double buffering is not enough. Maybe it was a very old project and new ones have that setting by default...

If someone would still look an answer for this, I used a timer for a slight delay and it solved the problem nicely. I wanted to highlight (change colour) for the entire row on mouse move event, but I think it would work for item replacement etc. For me listView.BeginUpdate() and listView.EndUpdate() didn't work, DoubleBuffered property also didn't work, I have googled a lot and nothing worked.
private int currentViewItemIndex;
private int lastViewItemIndex;
private void listView_MouseMove(object sender, MouseEventArgs e)
{
ListViewItem lvi = listView.GetItemAt(e.X, e.Y);
if (lvi != null && lastViewItemIndex == -1)
{
listView.Items[lvi.Index].BackColor = Color.Green;
lastViewItemIndex = lvi.Index;
}
if (lvi != null && lastViewItemIndex != -1)
{
currentViewItemIndex = lvi.Index;
listViewTimer.Start();
}
}
private void listViewTimer_Tick(object sender, EventArgs e)
{
listView.BeginUpdate();
listView.Items[lastViewItemIndex].BackColor = Colour.Transparent;
listView.Items[currentViewItemIndex].BackColor = Colour.Green;
listView.EndUpdate();
lastViewItemIndex = currentViewItemIndex;
listViewTimer.Stop();
}