Android app crashes when nothing is entered and button is pressed

问题

Hi I am working on an Android App and would like to ask for some help: The user enters a numbers on a editText and presses/clicks the button to get a conversion displayed in answer field text.

Unfortunately if nothing is entered and the user clicks the button the application crashes.

Could anyone help me put it into code:

If editText is empty and button is clicked display 0.00 in the answer text field.

or the other way if editText is empty and button is pressed display toast message

If anyone understands what I am talking about and can help I would greatly appreciate it as I want to improve my applications for users before publishing ;-)

my updated code:

    EditText editText = (EditText)findViewById(R.id.editText);
Double num1 = 0.0;
final String myStr = editText.getText().toString();
if (!myStrisEmpty())
{
    num1 = Double.parseDouble(myStr);
}
else
{
    Toast.makeText(getApplicationContext(), getResources().getString(R.string.noinput),
        Toast.LENGTH_LONG).show();
}

Problem is this: final String myStr = editText.getText().toString(); //editText is in red if (!myStrisEmpty()) //(!myStrisEmpty()) is in red

Ive been trying for hours and days to acomplish this task. simply have made a app where the user enters a number then clicks the button to convert the number and display it below into a textview answer. If i dont enter anything and click the button the app crashes. I would like a toast message instead of it crashing saying "Please Enter a Number"

回答1:

You are trying to convert an empty string to a number.
What you should do is a check if the string is not empty:

Change these lines:

EditText editText = (EditText) findViewById(R.id.editText);
Double num1 = Double.parseDouble(editText.getText().toString());

EditText editText = (EditText)findViewById(R.id.editText);
Double num1 = 0.0;
final String myStr = editText.getText().toString();
if (!myStr.isEmpty())
{
    num1 = Double.parseDouble(myStr);
}
else
{
    Toast.makeText(getApplicationContext(), getResources().getString(R.string.noinput),
        Toast.LENGTH_LONG).show();
}

You might replace getResources().getString(R.string.noinput) (set it in your /values/strings.xml folder) by a hardcoded string (but that's not a good practice), like "You didn't enter any value"

And this:

answer.setText(ans.toString());

should be:

answer.setText("" + ans);

回答2:

If i understood you weel, what you are trying to achieve is this:

String input = editText.getText().toString();
    if (input.isEmpty())
        textView.setText("0.00");
    else{
    // do whatever conversions
        textView.setText(result);
   }