Android application crashing despite exception caught

I'm writing a simple app which allows a user to enter their income and it deducts tax, then saves the amount in a file for future reference. Whenever I try to enter an amount I get a warning saying the application has stopped unexpectedly. Here is my code:

public void onClick(View v) {
    // TODO Auto-generated method stub
    try {

        if (preTax !=null){         
            Double incomeAmount = Double.parseDouble(preTax.getText().toString());
            incomeAmount =- (20 *100)/incomeAmount;     
            Double incomeRounded = Round(incomeAmount);
            Toast.makeText(null, "Your income minus tax = "+incomeRounded, Toast.LENGTH_LONG).show();


            FileOutputStream fos = ope开发者_JAVA百科nFileOutput("income", Context.MODE_PRIVATE);
            fos.write("1000".getBytes());
            fos.close();
        }
        else {

            Double incomeAmount = Double.parseDouble(postTax.getText().toString());
            Double incomeRounded = Round(incomeAmount);
            Toast.makeText(null, "Your income is: "+ incomeRounded, Toast.LENGTH_LONG).show();


            FileOutputStream fos = openFileOutput("income", Context.MODE_PRIVATE);
            fos.write("1000".getBytes());
            fos.close();
        }

    } catch (Exception e){
        Toast.makeText(null, "Please fill in the catagories" + e, Toast.LENGTH_LONG).show();
    }
}

This issue was happening before the fileoutstream stuff was added, so I know that that isn't the issue, but it is not clear to me what is. Program crashes regardless of whether the EditText is empty or not. Surely the try/catch should catch any errors?

Toast.makeText(null, "Please fill in the catagories" + e, Toast.LENGTH_LONG).show();

should be

Toast.makeText(v.getContext(), "Please fill in the catagories" + e, Toast.LENGTH_LONG).show();

you can't pass null in for the context, it needs to be valid.

Passing in null for the context does not exactly help. Your app in blowing up, getting caught and then blowing up again.