当 EditText 为空时 Android 应用程序崩溃

Question

I have a problem, that i can't solve, and solution of teacher doesn't work.

The problem is when I click "Check the answer" and nothing is written in EditText , the program crashes. I work in Android Studio.

Java code:

public class Main extends AppCompatActivity {
    int a, b, c, d;
    Button Enter, NewExercise, EndLesson;
    EditText et;
    TextView tv;
    ImageView iv;
    String st;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv = (TextView) findViewById(R.id.tv);
        et = (EditText) findViewById(R.id.et);
        iv = (ImageView) findViewById(R.id.iv);
        a = (int)(10 * Math.random());
        b = (int)(10 * Math.random());
        c = a + b;
        tv.setText("Exmaple: " + a + " + " + b);
        et.setText("" + c);
    }

    public void Show(View view) {
        a = (int)(10 * Math.random());
        b = (int)(10 * Math.random());
        c = a + b;
        tv.setText("" + a + " + " + b);
        et.setText("");
    }

    public void Check(View view) {
        st = et.getText().toString();
        d = Integer.parseInt(st);
        if(0 == et.length()) {
            Toast.makeText(this,"Please, enter the answer",Toast.LENGTH_LONG).show();
        }
        if (d == c) {
            iv.setImageResource(R.drawable.t);
            Toast.makeText(this, "Right", Toast.LENGTH_LONG).show();
        }
        else {
            Toast.makeText(this, "False", Toast.LENGTH_LONG).show();
            iv.setImageResource(R.drawable.f);
            et.setText("");
        }
    }
}

Xml:

<TextView
    android:layout_width="wrap_content"
    android:textSize="30dp"
    android:textColor="#000000"
    android:layout_height="wrap_content"
    android:id="@+id/tv" />

<ImageView
    android:layout_width="match_parent"
    android:layout_height="71dp"
    app:srcCompat="@drawable/eq"
    android:id="@+id/eq" />

<EditText
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:inputType="number"
    android:textSize="30dp"
    android:hint="Enter the answer"
    android:ems="10"
    android:maxLength="3"
    android:gravity="center"
    android:id="@+id/et"
    android:layout_weight="0.13" />

<ImageView
    android:layout_width="match_parent"
    android:layout_height="48dp"
    app:srcCompat="@drawable/t"
    android:id="@+id/iv"
    android:layout_weight="0.12" />

<Button
    android:text= "Check the answer"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:onClick="Check"
    android:id="@+id/CheckTheAnswer" />

<Button
    android:text= "New Exercise"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:onClick="Show"
    android:id="@+id/NewExercise" />

<Button
    android:text="End lesson"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:onClick="Exit"
    android:id="@+id/EndLesson" />

I'm sorry for my English. Thank you in advance.

Answer 1

That's because you are parsing empty string (ie "") to int which is causing crash.

You should carefully handle exception while parsing String to int using try-catch, because if String can't be parsed into int then it throw Runtime error, which will cause application to crash.

Answer 2

Make a check to the EditText if it is empty or not using this:

protected boolean isEmpty(EditText editText) {
        return (editText.getText().toString().equals(""));
    }

Hope this helps.

Answer 3

Try putting a null checker. Example:

if(et != null){
  st = et.getText().toString().trim();
       d = Integer.parseInt(st);
}

I added trim() method as well to trim trailing and leading white spaces.

Answer 4

Thanks for answers, but only this solution work.

if (st.equals(""))
    {
  vbsays.setText("< First, you need to enter something into the text box, and then check your answer. Try!");
    }
    else 
{
        d = Integer.parseInt(st);
}

Answer 5

the return type of getText() is editable so we need to convert it into string by using toString().

if(t1.getText().toString().equals("")// t1 is Edittext(class) object
   {
       Toast.makeText(MainActivity.this, "my Message", Toast.LENGTH_LONG).show();
   }
else
   {
       //do ur operation
   }