When developing functionalities in this way, we need to pay attention to the input of information, mainly ensuring whether it is valid or not.
In your case, I see two big points that could cause failure in your application:
1) - The user enter numeric alpha values, ie numbers and letters. If you try to do something similar to:
double num1 = Double.parseDouble("a");
You will receive Exception:
Caused by: java.lang.NumberFormatException: Invalid double: "a"
To prevent this, you need ensure that the user will only enter values valid in his EditText. For this, you can put the attribute inputText="number" directly in the xml of your component. This will make the keyboard style open for the user to enter the information of type number, that is, making it impossible for the user to enter letters:
<EditText
android:id="@+id/seu_id"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="Insira um valor"
android:inputType="number"/>
2) The user presses the button calcular forgetting to put valid information, for example, started typing and deleted all values and the EditText be empty. It would be like you trying to do this:
double num1 = Double.parseDouble("");
You will receive Exception:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.trim()' on a null object reference
To avoid this, you need to make a simple entry validation, to block the operation if invalid:
botaoCalcular.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
String primeiroTexto = primeiro.getText().toString();
String segundoTexto = segundo.getText().toString();
if(validaInformacao(primeiroTexto, segundoTexto)){
double num1 = Double.parseDouble(primeiroTexto);
double num2 = Double.parseDouble(segundoTexto);
double res = num2 - num1;
AlertDialog.Builder dialogo = new AlertDialog.Builder(MainActivity.this);
dialogo.setTitle("Resultado");
dialogo.setMessage("Resultado : " + res);
dialogo.setNeutralButton("OK", null);
dialogo.show();
}
}
});
private boolean validaInformacao(String primeiroTexto, String segundoTexto) {
if (TextUtils.isEmpty(primeiroTexto)) {
Toast.makeText(this, "O primeiro valor é inválido", Toast.LENGTH_SHORT).show();
return false;
} else if (TextUtils.isEmpty(segundoTexto)) {
Toast.makeText(this, "O segundo valor é inválido", Toast.LENGTH_SHORT).show();
return false;
} else {
return true;
}
}
On which line does the error?
– Ricardo
Probably the error occurs because you are trying to subtract the variable with NULL value, if this is the case you should check if it is null and put 0 in place.
– Antonio Raichaski
It is not agreeing any error the way it is but if I do not put some value in the field at the time it is executing that the error happens and the application is closed, I wonder how I can solve it
– Fernando Tricks Combo
If you have no data in the field, you will be converting null to double. Hence the error, probably nullpointerException. Validate the field by checking if it is not null before performing the operation.
– user28595
Look at this reply a way to prevent this error from occurring without validation.
– ramaral
Which error occurs, is really the
NullPointerException?– Guilherme Nascimento
@ramaral even if the fields come with default value, nothing prevents a user from deleting and trying to do the empty operation, validation would not be a way to protect itself from that?
– user28595
You are right @Diegofelipe, the fact of initializing the field and can only accept numbers does not prevent the user to make it null.
– ramaral