Restricting input length and characters for Entry field in Xamarin.Forms

Restricting input length and characters for Entry field in Xamarin.Forms

How can I restrict the length and characters entered in an Entry control in Xamarin.Forms. Do I need to create a custom control? Is there a way I can derive from Entry (or another control) so I can apply the necessary per-platform input limitations.

An example would be a numeric field that is restricted to a maximum of 3 characters, digits only.

Setting the Keyboard property of an Entry control to Keyboard.Numeric only sets the keyboard for iOS. It does not restrict the actual text entry - i.e. I can still enter non-digit characters. Nor do I see a way to limit the length of entry.

Answer by Pete for Restricting input length and characters for Entry field in Xamarin.Forms

There appears no in-built properties to restrict character / length in the Entry control. You could accomplish both the text limiting and character input via one of the following two methods available:-

1) Yes - you can derive directly from Entry to create you own derivation of this and then customize it further, for instance hooking into the TextChanged event handler. There is no handler for a key-press, so you would have to do your validity checking on the complete values passed into e.NewTextValue. If the new entry doesn't match within your requirements you could then just set the .Text=e.OldTextValue to revert to the last valid entry.

2) If you wanted to hook into the event handlers for the each platform native-controls you could write your own custom renderer controls to have finer control.

Answer by Femil Shajin for Restricting input length and characters for Entry field in Xamarin.Forms

You can restrict the number of charecters in the Entry field as given below,

  int restrictCount =  //Enter your number of character restriction    Entry entry = new Entry();    entry.TextChanged += OnTextChanged;      void OnTextChanged(object sender, EventArgs e)    {      Entry entry = sender as Entry;      String val = entry.Text; //Get Current Text        if(val.Length > restrictCount)//If it is more than your character restriction      {       val = val.Remove(val.Length - 1);// Remove Last character        entry.Text = val; //Set the Old value      }    }  

Answer by Mark Carew for Restricting input length and characters for Entry field in Xamarin.Forms

Have a look at Xamarin Behaviors. There is TextChangedBehavior.cs that you can use a template for developing your own behaviors to cater for formatted masked text entry fields. I have developed FormattedTextChangedBehavior : Behavior for just this purpose.

Answer by Ian J. for Restricting input length and characters for Entry field in Xamarin.Forms

A continuation of Femil's answer:

Here's a custom control for limiting the number of characters, but it could be used for anything you want to use TextChanged for:

public class CustomEntry : Entry  {      private CustomEntryParams parameters { get; set; }        public CustomEntry(CustomEntryParams customParams)      {          if (customParams.MaxLength > 0)          {              base.TextChanged += EnforceMaxLength;              parameters = customParams;          }      }        public void EnforceMaxLength(object sender, TextChangedEventArgs args)      {          Entry e = sender as Entry;          String val = e.Text;            if (val.Length > parameters.MaxLength)          {              val = val.Remove(val.Length - 1);              e.Text = val;          }      }  }    public class CustomEntryParams {      public int MaxLength { get; set; }  }  

Don't try to use this in the XAML, you will receive a parser error, instead use it in the codebehind:

new CustomEntry(new CustomEntryParams { MaxLength = 5 });  

Answer by user2635746 for Restricting input length and characters for Entry field in Xamarin.Forms

I used a custom entry control with Bindable properties for uppercase and maximum length.

Control (MyEntry.cs)

        class NewPaymentEntry : Entry  {     public NewPaymentEntry()      {          base.TextChanged += EditText;      }      public void EditText(object sender, TextChangedEventArgs args)      {          Entry e = sender as Entry;          String val = e.Text;            if (string.IsNullOrEmpty(val))              return;            if (Uppercase )              val = val.ToUpper();            if(MaxLength > 0 && val.Length > MaxLength)          {                  val = val.Remove(val.Length - 1);          }          e.Text = val;        }        public static readonly BindableProperty UppercaseProperty = BindableProperty.Create(p => p.Uppercase, false);        public bool Uppercase      {          get          {              return (bool)GetValue(UppercaseProperty);          }          set          {              SetValue(UppercaseProperty, value);          }      }        public static readonly BindableProperty MaxLengthProperty = BindableProperty.Create(p => p.MaxLength, 0);        public int MaxLength      {          get          {              return (int)GetValue(MaxLengthProperty);          }          set          {              SetValue(MaxLengthProperty, value);          }      }  }  

Call it from xaml like

Answer by joacar for Restricting input length and characters for Entry field in Xamarin.Forms

I would definitely use a behvaior for this

public class TextValidationBehavior : Behavior  {   // This can be bound to view model property to be informed   public static readonly BindableProperty IsValidProperty = IsValidPropertyKey.BindableProperty;      public bool IsValid      {          get { return (bool)base.GetValue(IsValidProperty); }          private set { base.SetValue(IsValidPropertyKey, value); }      }    // Attach delegate to text changed event  protected override void OnAttachedTo(Entry entry)  {      entry.TextChanged += OnEntryTextChanged;      base.OnAttachedTo(entry);  }  // Detach delegate from text changed event  protected override void OnDetachingFrom(Entry entry)  {      entry.TextChanged -= OnEntryTextChanged;      base.OnDetachingFrom(entry);  }    void OnEntryTextChanged(object sender, TextChangedEventArgs e)  {      var text = e.NewTextValue;      IsValid = Validate(text); // Implement this as needed  }  }  

Then use it in xaml like this

Answer by Shyju M for Restricting input length and characters for Entry field in Xamarin.Forms

You can set the filters as below in the OnElementChanged method from the custom renderer

this.Control.SetFilters(new Android.Text.IInputFilter[] { new Android.Text.InputFilterLengthFilter(MaxLength)});  

Answer by Umut Bebek for Restricting input length and characters for Entry field in Xamarin.Forms

You can just use Binding; For example i want to hold a payment value that can not exceed 100. So i wrote a class

puclic class Payment : INotifyPropertyChanged  {      private int _amountDecimals;      public int AmountDecimals      {          get          {              return _amountDecimals;          }            set          {              if (value <= 100)              {                  _amountDecimals = value;              }              OnPropertyChanged();          }      public event PropertyChangedEventHandler PropertyChanged;        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)      {          PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));      }  }  

So this property will set AmountDecimals value if user enters a value until it not exceeds 100

Then just set binding via code on Page constructor(or from xaml)

var myPayment =new Payment(); //this will hold page(view) data  BindingContext = myPayment;  var paymentEntry = new Entry();  paymentEntry.Keyboard = Keyboard.Numeric;  paymentEntry.SetBinding(Entry.TextProperty, "AmountDecimals");              

So user enters a numeric value to the entry, but if he/she tries to enter a value more than 100, binding just reverse it to old value. You can just write your code to your class's properties like this (on setters). So if you want to some property to carry only 5 characters you can write something like this (codes can be wrong i did not compiled them :) )

    private string _name;      public string Name      {          get          {              return _name;          }            set          {              if ((value!= null && value.length <= 5) || value == null)              {                  _name = value;              }              OnPropertyChanged();          }  

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