当EditText为空时防止nullPointerException

Question

Hi I am making an app to calculate averages with user input from EditTexts. When I run the app it works, but when I leave a field blank it throws a nullPointerException. I know what it is and how I can fix them in general. With my code I was thinking of using an if statement to check if its empty. But I don't know how to check for a empty/null value with integers. Could someone explain whats the best way/practice for checking this?

Any tips etc. are welcome!

My code:

final Button calculateButton = findViewById(R.id.calculateAverageButton);
calaculateButton.setOnClickListener(new  View.onClickListener() {
public void onClick(View v) { TextView averageView = findViewById(R.id.averageView);

int grade[] = {Integer.parseInt(((EditText) findViewById(R.id.grade1)).getText().toString());
int weight[] = {Integer.parseInt(((EditText)  findViewById(R.id.weight1)).getText().toString());

int weightTotal = weight[0];

int sum = grade[0] * weight[0];

int average = sum / weightTotal

String averageText = getString(R.string.average);
averageView.setText(averageText + Integer.toString(average));

Answer 1

This is why you should avoid doing a lot of inline code.

There is no such thing as an empty integer, you need to check the string from the edit text

String value = ((EditText) findViewById(R.id.grade1)).getText().toString();
if(value != null && value.length() > 0){
    try{
        //Since edit text gives you a string you cannot guarantee you have a number input
        int numberValue = Integer.parseInt(value);
    catch(NumberFormatException e){
        //handle exception
    }
}

Answer 2

I would recommend to this to check if editText is empty or not :

if(editText.length()>0){
        //there is text
    }else{
        //your code in case of empty editText
    }

Answer 3

first of all don't initiate your views (eg : averageView) inside button click listener , put this line :

TextView averageView = findViewById(R.id.averageView);

to out of your button's click listener block

String has a isEmpty() function so in order to check for empty string, before initiate your grade[] :

EditText grades = ((EditText) findViewById(R.id.grade1));
if (!grades.getText().toString().isEmpty())
    do your logic here
else
    show some error

Answer 4

Welcome to SO @J.Doe

There are many points about your code.

anyway, i have tried to quickly mentionned some of them and modified it to look like this :

  final Button calculateButton = findViewById(R.id.calculateAverageButton);
 EditText e1 = (EditText) findViewById(R.id.grade1);
 EditText e2 = ((EditText)  findViewById(R.id.weight1);
TextView averageView = findViewById(R.id.averageView);
calaculateButton.setOnClickListener(new  View.onClickListener() {
  public void onClick(View v) {

     /** better practice for checking NullPointerException **/
 if(e1.getText() || e2.getText()){
  Log.d(TAG, "Null values");
return;
 }

String txt1 =  e1.getText().toString();
 String tx2 =  e2.getText().toString();

 boolean emptyE1 = txt1.equals("");
boolean emptyE2 = txt2.equals("");

 /** Checking for empty values **/
  if(emptyE1 || emptyE2){
Log.d(TAG, "Empty values");
return;
 }

   int grade;
 int weightTotal;

/** You have also to   ensure that the strings are numeric**/
try{
grade = new Integer(txt1);
 weightTotal = new Integer(txt1);
  }
 catch(NumberFormatException e){){
   Log.d(TAG, "Number input required");
   return;
      }

          /** Now, you are sure you have received numbers :) **/



      int sum = grade  * weight; // sum ? ;)

 int average = sum / weightTotal

    String averageText = getString(R.string.average);
   averageView.setText(averageText + Integer.toString(average));

      }