Set at least one number in Edittext

Question

My question is this::

Is there any way to prevent the click of a button if an Edittext has no number at all? I was able to limit minimum and maximum values (0 to 255), but I could not find a solution to this problem. Because "" is not an integer value, by clicking the button without filling the three fields with some number, the app crasha.

I tried to use this medium, but I was unsuccessful:

btnCalc.setOnClickListener (new View.OnClickListener()
            {
                public void onClick(View v)
                {   
                    if (edtRed == null || edtGreen == null || edtBlue == null)
                    {
                        btnCalc.setEnabled(false);
                    }
                    else
                    {
                        btnCalc.setEnabled(true);
                        getCode();
                    }
                    if (n1 > 255 || n1 < 0 || n2 > 255 || n2 < 0 || n3 > 255 || n3 < 0)
                    {
                        result = "#FFFFFF";
                        txtResult.setText(result);
                    }
                    else
                    {           
                        Calculate();
                    }   
                    result = "#" + rst1 + remainderR + rst2 + remainderG + rst3 + remainderB;
                    txtResult.setText(result);
                }               
            });

Answer 1

Test the size of the Edittext content in the Editor which indicates that there has been a change in it, if the content size of your Edittext is greater than zero enable the button, otherwise disable.

As the author of the question observed himself, the button should be initialized already disabled, because Edittext starts empty. It can be disabled in both xml and code.

Example:

btnOk = (EditText)findViewById(R.id.btnOk);
btnOk.setEnabled(false); //já inicia desabilitado
txtQuantidade = (EditText)findViewById(R.id.txtQuantidade);
txtQuantidade.addTextChangedListener(new TextWatcher(){
    public void afterTextChanged(Editable s) {
        if(txtQuantidade.length() > 0 ) { //verifica tamanho do conteúdo do EditText
            btnOk.setEnabled(true);       //habilita botão
        }
        else {
            btnOk.setEnabled(false);      //desabilita botão
        }
    }
    public void beforeTextChanged(CharSequence s, int start, int count, int after){}
    public void onTextChanged(CharSequence s, int start, int before, int count){}
}); 

Your content will always be a number, because as you said yourself your Edittext accepts only numbers:

<EditText
    android:id="@+id/txtQuantidade"
    android:inputType="number" //aceita apenas números
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_below="@+id/textView1"
    android:ems="10" >
</EditText>