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How to validate Entry control on Button clicked Event and Textchanged event in xamarin.forms?


How to validate Entry control on Button clicked Event and Textchanged event in xamarin.forms?

By : Aniket Shinde
Date : December 01 2020, 05:00 PM
around this issue How to validate Entry control in xamarin.forms ?
code :
RegisterButton.Clicked += (sender, e) => {

  if (Validate()) {
    // complete Registration process
  }

};

private bool Validate() {

  // perform test for each field on page
  if (string.IsNullOrEmpty(NameField.Text)) {
    DisplayAlert("Error","Please enter a value for Name", "OK");
    return false;
  }

  // repeat for next field - some fields may have different, 
  // or multiple validations, depending on your business rules

  // if all validations pass, then return true
  return true;
}


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Bind Entry TextChanged to the CanExecute method of button command in Xamarin.Forms

Bind Entry TextChanged to the CanExecute method of button command in Xamarin.Forms


By : Arthur McKerry
Date : March 29 2020, 07:55 AM
like below fixes the issue Usually, in order to react to a view event using MVVM pattern, it is recommended that you use EventToCommandBehaviour.
But in this case it is not needed, as the setters on properties bound to Entry should trigger every time text changes. You can use that to trigger ChangeCanExecute() on command to notify view that the button can now be enabled/disabled.
code :
string _firstName;
public string FirstName
{
    get { return _firstName; }
    set
    {
        if (_firstName != value)
            SendCommand.ChangeCanExecute();
        SetProperty(ref _firstName, value, nameof(FirstName));
    }
}

string _lastName;
public string LastName
{
    get { return _lastName; }
    set
    {
        if (_lastName != value)
            SendCommand.ChangeCanExecute();
        SetProperty(ref _lastName, value, nameof(LastName));
    }
}

string _email;
public string Email
{
    get { return _email; }
    set
    {
        if (_email != value)
            SendCommand.ChangeCanExecute();
        SetProperty(ref _email, value, nameof(Email));
    }
}

Command _sendCommand;
public Command SendCommand 
{
    get
    {
        return _sendCommand ?? (_sendCommand = new Command(OnSend, CanSend));
    }    
}

bool CanSend(object obj)
{
    return Validate();
}

void OnSend(object obj)
{
    if(Validate())
    {
        //actual button click execution
    }
}

bool Validate()
{
    // disable button if any entry empty
    return !string.IsNullOrEmpty(_firstName)
                  && !string.IsNullOrEmpty(_lastName)
                  && !string.IsNullOrEmpty(_email);
}
Xamarin Forms - include a parameter on the clicked event of a button

Xamarin Forms - include a parameter on the clicked event of a button


By : Prajwal Patil
Date : March 29 2020, 07:55 AM
this one helps. I also suggest you to go with MVVM. You can set PINNO in ViewModel. Create PINNOproperty with backing field in ViewModel as:
code :
string pinNo="";
public string PINNO
{
    get { return pinNo; }
    set
    {
       pinNo=value;
       OnPropertyChanged();
    }
}
Text={Binding PINNO} Command={Binding PinButtonCommand}
public ICommand PinButtonCommand { get; private set; }
PinButtonCommand=new Command(Dosomething);
void Dosomething()
{
    //Use the PINNO Property here
}
How to get button clicked event in ViewCellRenderer Xamarin.Forms

How to get button clicked event in ViewCellRenderer Xamarin.Forms


By : Chandana
Date : March 29 2020, 07:55 AM
it should still fix some issue If i understand correctly, the button inside the viewcell is not exposed, so you can create public event inside the viewcell for the button click event ,and invoke it when clicking the button.
Complete Code
code :
public delegate void ClickEventHandler(object sender, EventArgs e);
public event ClickEventHandler ClickEvent;

void ButtonClick(object sender, EventArgs args)
{
    ClickEvent(this, args);
}
//.xmal
<ListView x:Name="listView"  RowHeight="50">
    <ListView.ItemTemplate>
        <DataTemplate>
            <local:CustomViewCell ClickEvent="ButtonClick"/>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

//.cs    
void ButtonClick(object sender, EventArgs args)
{
    CustomViewCell cell = sender as CustomViewCell;
    object context = cell.BindingContext;//here you can get index or something else
}
Xamarin entry control TextChanged event looping round

Xamarin entry control TextChanged event looping round


By : user1271220
Date : March 29 2020, 07:55 AM
I wish did fix the issue. The way that I resolved this issue in the end was using a separate class to handle my validations.
My validation class:
code :
using System.ComponentModel;
using System.Runtime.CompilerServices;

public class viewModel : INotifyPropertyChanged
{
 public event PropertyChangedEventHandler PropertyChanged;

 private string age_;
 public string Age { get { return age_; } set { if (age_ != value) { age_ = ProcessAge(value); OnPropertyChanged(); } } }

 private string ProcessAge(string age)
 {
    if (string.IsNullOrEmpty(age))
        return age;

    if (age.Length > 3)
        age = age.Substring(0, 3);

    if (age.StartsWith("0"))
        age = age.Remove(0, 1);

    return age.Replace(".", "").Replace("-", "");
 }

 private void OnPropertyChanged([CallerMemberName] string propertyName = null)
 {
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
 }
}
public MainPage()
    {
        InitializeComponent();
        BindingContext = new viewModel();
    }
Text="{Binding Age, Mode=TwoWay}"
Xamarin.Forms - doesn't match event type bug in clicked event

Xamarin.Forms - doesn't match event type bug in clicked event


By : Doug Miller
Date : March 29 2020, 07:55 AM
This might help you i don't know what is the problem here it works properly before the update, it started after i update xamarin to the latest version few days ago and all of my clicked event in xaml became like this in the image , clicked event is expecting return
code :
private async void btnPlaceorder_Clicked(object sender, EventArgs e)
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