如果按下按钮时 edittext 部分为空白，我想显示 toast 错误消息 (Android Studio)

Question

I made a simple calculator app in android studio but the app crashes when no value is entered in the edittext section. I want to show a toast msg when no value is entered in the edittext section. Please check this issue and guide me how to fix this and add toast. here n1 and n2 is the id of edittext.

MainActivity (code):

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    n1 = findViewById(R.id.n1);
    n2 = findViewById(R.id.n2);
    add = findViewById(R.id.add);
    sub = findViewById(R.id.sub);
    multi = findViewById(R.id.multi);
    div = findViewById(R.id.div);
    tv = findViewById(R.id.tv);

    // addition part

    add.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            int p,q,r;
            p = Integer.parseInt(n1.getText().toString());
            q = Integer.parseInt(n2.getText().toString());
            r = p+q;
            tv.setText("Result is " + r);
            Toast.makeText(MainActivity.this, "Successfully Calculated", Toast.LENGTH_SHORT).show();

        }
    });
    //subtraction part

    sub.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            int p,q,r;
            p = Integer.parseInt(n1.getText().toString());
            q = Integer.parseInt(n2.getText().toString());
            r = p-q;
            tv.setText("Result is " + r);
            Toast.makeText(MainActivity.this, "Successfully Calculated", Toast.LENGTH_SHORT).show();

        }
    });

    // multiplication part

    multi.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            int p,q,r;
            p = Integer.parseInt(n1.getText().toString());
            q = Integer.parseInt(n2.getText().toString());
            r = p*q;
            tv.setText("Result is " + r);
            Toast.makeText(MainActivity.this, "Successfully Calculated", Toast.LENGTH_SHORT).show();

        }
    });

    //divison part

    div.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            int p,q,r;
            p = Integer.parseInt(n1.getText().toString());
            q = Integer.parseInt(n2.getText().toString());
            r = p/q;
            tv.setText("Result is " + r);
            Toast.makeText(MainActivity.this, "Successfully Calculated", Toast.LENGTH_SHORT).show();

        }
    });

}

}

Answer 1

Do the same in all the other OnClickListner

add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int p,q,r;
                if(!n1.getText().toString().equals("") && !n2.getText().toString().equals("")) {
                    p = Integer.parseInt(n1.getText().toString());
                    q = Integer.parseInt(n2.getText().toString());
                    r = (p + q);
                    Toast.makeText(MainActivity.this, "Successfully Calculated", Toast.LENGTH_SHORT).show();
                    tv.setText("Result is " + r);
                }else {
                    Toast.makeText(MainActivity.this, "Error", Toast.LENGTH_SHORT).show();

                }
            }
        });

Answer 2

You could do a preliminary check to see if any text was entered like

if(n1.getText()) ....

Ideally you'd want to surround the ParseInt() with a try{}..catch{} block and handle any errors there to stop the app from crashing.

Answer 3

  int n1Value = n1.getText().toString();
  int n2Value = n2.getText().toString();
  p = n1Value !=null&&!n1Value.isEmpty()? Integer.parseInt(n1Value):0 
  p = n2Value !=null&&!n2Value.isEmpty()? Integer.parseInt(n2Value):0 

Add this in your click listeners. the crash is happening because you don't have any null check.