How can restrict my EditText input to some special character like backslash(/),tild(~) etc by soft keyboard in android programmatically

I am developing an application for keyboard, but i am geting an issue. I want to restrict/block some special character from soft keyboard in EditText in android programmatically.

So, Is there any way i can restrict any special character input in edit text in android.

If anyone have idea,Please reply.

Thanks in advance.

Try this may work for you

public class MainActivity extends Activity {

	private EditText editText;
	private String blockCharacterSet = "~#^|$%&*!";

	private InputFilter filter = new InputFilter() {

		@Override
		public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {

			if (source != null && blockCharacterSet.contains(("" + source))) {
				return "";
			}
			return null;
		}
	};

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		editText = (EditText) findViewById(R.id.editText);
		editText.setFilters(new InputFilter[] { filter });
	}

}

If you want to add spaces you can give space after the last digit.

  android:digits="0123456789qwertzuiopasdfghjklyxcvbnm "

This should work:

InputFilter filter = new InputFilter() { 
        public CharSequence filter(CharSequence source, int start, int end, 
Spanned dest, int dstart, int dend) { 
                for (int i = start; i < end; i++) { 
                        if (!Character.isLetterOrDigit(source.charAt(i))) { 
                                return ""; 
                        } 
                } 
                return null; 
        } 
}; 

edit.setFilters(new InputFilter[]{filter});

Or if you prefer the easy way:

<EditText android:inputType="text" android:digits="0123456789*,qwertzuiopasdfghjklyxcvbnm" />

check this link which shows How to restrict special characters from an Android EditText field?

Try this code android:digits="abcde.....012345789" i guess this is the easiest way to do.Hope this help you.

Its late but may be helpfull for others. Instead of programaticaly, you can go with xml attribute. It may be the case that in Single layout you have many editText, out of which you wanna restrict special characters only in one EditText. So defining in xml will help you out. Here is the code to restrict special Characters by allowing them to only enter alphabets and numbers like below

<EditText
     android:id="@+id/editText"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:textSize="@dimen/text10"
     android:singleLine="true"
     android:maxLines="1"
     android:maxLength="16"
     android:digits="abcdefghijklmnopqrstuvwxyz0123456789"/>

For those who might be facing issues while adding space please add a blank space with all the alphabets. Below is an example Also you should know that user won't be able to add a new line in this case.

            <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:inputType="text"
            android:digits="0123456789,a bcdefghijklmnopqrstuvwxyz"
            android:maxLines="1"
            android:singleLine="true" />

First need to add DigitsKeyListener for allowing characters and then setRawInputType to edittext field

edit_field.setKeyListener(DigitsKeyListener.getInstance("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"));


edit_field.setRawInputType(InputType.TYPE_TEXT_VARIATION_PERSON_NAME);

You can create regular expression and check it on onTextChanged method

yourEditText.addTextChangedListener(new TextWatcher() {

          public void afterTextChanged(Editable s) {

            // you can call or do what you want with your EditText here
            yourEditText. ... 

          }

          public void beforeTextChanged(CharSequence s, int start, int count, int after) {}

          public void onTextChanged(CharSequence s, int start, int before, int count) {}
       });

you can prevent for typing special character:

yourEditText.addTextChangedListener(new TextWatcher() {
      CharSequence previous;
      public void afterTextChanged(Editable s) {
        if(s.toString().contains("&^%$#*&(")){
              s.clear();
              s.append(previous.toString());
        }
      }

      public void beforeTextChanged(CharSequence s, int start, int count, int after) {    
            previous = s;
      }

      public void onTextChanged(CharSequence s, int start, int before, int count) {}
   });

Unfortunately the accepted solution doesn't work in all the cases. The proper solution would be to use the following InputFilter:

private InputFilter filter = new InputFilter() {
    // An example pattern that restricts the input only to the lowercase letters
    private static final Pattern restrictedChars = Pattern.compile("[a-z]*")

    @Override
    public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
        final CharSequence replacementText = source.subSequence(start, end);
        final CharSequence replacedText = dest.subSequence(dstart, dend);

        if (source == null || restrictedChars.matcher(replacementText).matches()) {
            return null; // Accept the original replacement
        }

        return replacedText; // Keep the original text
    }
};

This solution differs from the accepted one in that it solves the following problems:

• only a subsequence of the source is the replacement, not the full source
• source doesn't necessarily include only the newly typed text, sometimes it is the full text typed so-far

kotlin version of this answer

class NameActivity : AppCompatActivity() {

  var myFilter =
    InputFilter { source, _, _, _, _, _ ->
        try {
            val c = source[0]
            return@InputFilter if (Character.isLetterOrDigit(c)  || c == '_' || c == '.') {
                "$c"
            } else {
                // here you can show error msg
                ""
            }
        } catch (e: Exception) {
        }
        null
    }


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_name)
        val edittext = findViewById<EditText>(R.id.edittext)
        edittext.filters = (arrayOf(myFilter))
    }

}

This works for me...

android:digits="÷×=%_-+#().,abcdefghijklmnopqrstuvwxyzA BCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\n\u0020"

for space use:

\u0020

for new line use:

\n

for ime options use:

android:singleLine="true"
android:maxLines="1"

Hope it works for you...

The accepted answer still allows the user paste in unwanted characters. This solution works:

---

All you have to do is this:

List<String> unwantedChars = new ArrayList<>(Arrays.asList("@", "€"));
editText.addTextChangedListener(new FilterUnwantedChars(editText, unwantedChars));

Helper class:

public class FilterUnwantedChars implements TextWatcher {

    private List<String> unwantedChars;
    private EditText editText;

    private boolean listenToTextChange;

    public FilterUnwantedChars(EditText editText, List<String> unwantedChars) {
        this.unwantedChars = unwantedChars;
        this.editText = editText;
        this.listenToTextChange = true;
    }

    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) { }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
        if (!listenToTextChange) {
            listenToTextChange = true;
            return;
        }

        String result = s.toString();
        final String oldString = result;
        for (String unwanted : unwantedChars) {
            result = result.replace(unwanted, "");
        }

        if (!oldString.equals(result)) {
            listenToTextChange = false;
            int currentPos = editText.getSelectionStart()-1;
            editText.setText(result);

            try {
                editText.setSelection(currentPos);
            } catch (Exception e) {
                // nothing
            }
        }
    }

    @Override
    public void afterTextChanged(Editable s) { }

    public void setEditText(EditText editText) {
        this.editText = editText;
    }

    public EditText getEditText() {
        return editText;
    }

    public List<String> getUnwantedChars() {
        return unwantedChars;
    }

    public void setUnwantedChars(List<String> unwantedChars) {
        this.unwantedChars = unwantedChars;
    }
}

Can be solved by using filters, i.e.

val regex = Regex("^[~#^|$%&*!]*$")
val filter = InputFilter { source, _, _, _, _, _ ->
    return@InputFilter when {
        source?.matches(regex) == true -> ""
        else -> null
    }
}
editText.filters = arrayOf(filter)

and for handling copy-pasted text, can be done by adding condition to check if text inputted was greater than 1, which now looks like this

val regex = Regex("^[~#^|$%&*!]*$")
val filter = InputFilter { source, _, _, _, _, _ ->
    return@InputFilter when {
        source?.matches(regex) == true -> ""
        source.length > 1 -> source.trim { it.toString().matches(regex) } // Put your desired logic here, these sample logic was doing a trim/remove
        else -> null
    }
}
editText.filters = arrayOf(filter)