Physics app keeps crashing, how do I fix this?-CodePudding

I've run into a simple error with the app. How do I get a user input that is an integer to work with editText field. I have the editText input type set as "number".

EditText M1;
EditText M2;
EditText A1;
EditText A2;
Button answer;
TextView Resultant;
TextView Angle;

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

    M1 = (EditText) findViewById(R.id.Direction1);
    M2 = (EditText) findViewById(R.id.Direction2);
    A1 = (EditText) findViewById(R.id.Theta1);
    A2 = (EditText) findViewById(R.id.Theta2);

    Resultant = (TextView) findViewById(R.id.MagnitudeAnswer);

    double Vector1X;
    double Vector1Y;
    double Vector2X;
    double Vector2Y;

    double ResultantX;
    double ResultantY;

    double ResultantT;

    double Magnitude;

    //Double.parseDouble(M1.getText().toString());
    //Double.parseDouble(String.valueOf(M1));

    double D1 = Double.parseDouble(M1.getText().toString());
    double D2 = Double.parseDouble(M2.getText().toString());
    double angle1 = Double.parseDouble(A1.getText().toString());
    double angle2 = Double.parseDouble(A2.getText().toString());

    Vector1X = D1 * Math.cos(Math.toRadians(angle1));
    Vector1Y = D1 * Math.sin(Math.toRadians(angle1));

    Vector2X = D2 * Math.cos(Math.toRadians(angle2));
    Vector2Y = D2 * Math.sin(Math.toRadians(angle2));

    ResultantX = Vector1X   Vector2X;
    ResultantY = Vector1Y   Vector2Y;

    ResultantT = (ResultantX * ResultantX)   (ResultantY * ResultantY);
    Magnitude = Math.sqrt(ResultantT);



    answer = findViewById(R.id.Answer);
    answer.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Resultant.setText(String.valueOf(Magnitude));
        }
    });

This is all the code I have made, The error shows up in line 45 which is "double D1 = Double.parseDouble(M1.getText().toString());"

CodePudding user response：

I think you would want to move the calculation part of code inside the onClick()... something like this:

answer = findViewById(R.id.Answer);
answer.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        double D1 = Double.parseDouble(M1.getText().toString());
        double D2 = Double.parseDouble(M2.getText().toString());
        double angle1 = Double.parseDouble(A1.getText().toString());
        double angle2 = Double.parseDouble(A2.getText().toString());

        Vector1X = D1 * Math.cos(Math.toRadians(angle1));
        Vector1Y = D1 * Math.sin(Math.toRadians(angle1));

        Vector2X = D2 * Math.cos(Math.toRadians(angle2));
        Vector2Y = D2 * Math.sin(Math.toRadians(angle2));

        ResultantX = Vector1X   Vector2X;
        ResultantY = Vector1Y   Vector2Y;

        ResultantT = (ResultantX * ResultantX)   (ResultantY * ResultantY);
        Magnitude = Math.sqrt(ResultantT);
        Resultant.setText(String.valueOf(Magnitude));
    }
});

CodePudding user response：

You are trying to read / parse D1, D2, etc before the screen has been shown to the user. Naturally, the fields are blank.

CodePudding user response：

Yes. Sujal Kumar's answer works but as mentioned by Stephen.C in his comment we need to need to follow some precautions. These are the thing you need to follow

Check if the value is null or empty(It should not be)
Check if the value entered in a double

First we are going to check if the value entered in not empty. This code will work

answer = findViewById(R.id.Answer);
answer.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        if(M1.getText().toString().trim().isEmpty() || 
           M2.getText().toString().trim().isEmpty() ||
           A1.getText().toString().trim().isEmpty() ||
           A2.getText().toString().trim().isEmpty()){
           
           Toast.makeText(this, "One of the fields are empty", Toast.LENGHT_SHORT).show();
           return;
        }
        double D1 = Double.parseDouble(M1.getText().toString());
        double D2 = Double.parseDouble(M2.getText().toString());
        double angle1 = Double.parseDouble(A1.getText().toString());
        double angle2 = Double.parseDouble(A2.getText().toString());

        Vector1X = D1 * Math.cos(Math.toRadians(angle1));
        Vector1Y = D1 * Math.sin(Math.toRadians(angle1));

        Vector2X = D2 * Math.cos(Math.toRadians(angle2));
        Vector2Y = D2 * Math.sin(Math.toRadians(angle2));

        ResultantX = Vector1X   Vector2X;
        ResultantY = Vector1Y   Vector2Y;

        ResultantT = (ResultantX * ResultantX)   (ResultantY * ResultantY);
        Magnitude = Math.sqrt(ResultantT);
        Resultant.setText(String.valueOf(Magnitude));
    }
});

Now we need to check if the text is double or not. Try this code:

//add this method in the class
public static boolean isNumeric(String str) {
  return str.matches("-?\\d (\\.\\d )?");  //match a number with optional '-' and decimal.
}

// add this code for the on click listener.

answer = findViewById(R.id.Answer);
answer.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        if(M1.getText().toString().trim().isEmpty() || 
           M2.getText().toString().trim().isEmpty() ||
           A1.getText().toString().trim().isEmpty() ||
           A2.getText().toString().trim().isEmpty()){

           Toast.makeText(this, "One of the fields are empty", Toast.LENGHT_SHORT).show();
           return;
        }
        
        if(!isNumeric(M1.getText().toString().trim()) || 
           !isNumeric(M2.getText().toString().trim()) ||
           !isNumeric(A1.getText().toString().trim()) ||
           !isNumeric(A2.getText().toString().trim())){

           Toast.makeText(this, "One of the fields are not doubles", Toast.LENGHT_SHORT).show();
           return;
        }

        double D1 = Double.parseDouble(M1.getText().toString());
        double D2 = Double.parseDouble(M2.getText().toString());
        double angle1 = Double.parseDouble(A1.getText().toString());
        double angle2 = Double.parseDouble(A2.getText().toString());

        Vector1X = D1 * Math.cos(Math.toRadians(angle1));
        Vector1Y = D1 * Math.sin(Math.toRadians(angle1));

        Vector2X = D2 * Math.cos(Math.toRadians(angle2));
        Vector2Y = D2 * Math.sin(Math.toRadians(angle2));

        ResultantX = Vector1X   Vector2X;
        ResultantY = Vector1Y   Vector2Y;

        ResultantT = (ResultantX * ResultantX)   (ResultantY * ResultantY);
        Magnitude = Math.sqrt(ResultantT);
        Resultant.setText(String.valueOf(Magnitude));
    }
});