Question

I have an Activity with an EditText, Button and TextView. If I write some numbers and click the button, the TextView shows the result of the calculation.

If the EditText is empty (i.e. there are no numbers entered) and I click the Button I have the a dialog saying: “The application has stopped unexpectedly. Please try again”.

Please help me. I want to show a window with some comments (for example “Insert numbers”), if the user does not write any numbers. How should I program the EditText field?
How to solve this? Thanks a lot

This is my onClick method:

public void onClick(View v) {
    EditText numA  = (EditText)findViewById(R.id.editText1);
    TextView wynik1 = (TextView)findViewById(R.id.wynik);

    float num1 = Float.parseFloat(numA.getText().toString());

    float eq1 = 0;

    if(num1>0){ 
        switch (v.getId()) {
                case R.id.oblicz:
                    eq1 = 2*num1;
                break;
        }

        wynik1.setText(String.format("%f", eq1));   
    }
    else {
        Intent o = new Intent(this, Obliczokno.class);
        startActivity(o);
    }
}

I have changed onClick method:

public void onClick(View v) {
    EditText numA  = (EditText)findViewById(R.id.editText1);

    float num2 = Float.parseFloat(numA.getText().toString());
    float eq1 = 0;
    float eq2 = 0;  

    try{  float num1 = Float.parseFloat(numA.getText().toString());

            if(num1>0 || num2>0){   

                switch (v.getId()) {
                case R.id.pole:
                    eq1 = 2*num1 ;

                break;  

                case R.id.obwod:
                    eq2 = 3*num1 ;

                break;  

                }}

                else {Intent o = new Intent(this, Obliczokno.class);
                startActivity(o);}
        }
         catch (NumberFormatException e) {
           Toast.makeText(this, "Sorry you did't type anything", Toast.LENGTH_SHORT).show();

           return;
        }

and I have errors. My LogCat errors:

E/AndroidRuntime(321): Uncaught handler: thread main exiting due to uncaught exception
E/AndroidRuntime(321): java.lang.NumberFormatException:
E/AndroidRuntime(321):  at org.apache.harmony.luni.util.FloatingPointParser.parseFloat(FloatingPointParser.java:296)
E/AndroidRuntime(321):  at java.lang.Float.parseFloat(Float.java:327)

E/AndroidRuntime(321):  at arek.geometria.Oblicz.onClick(Oblicz.java:35)

E/AndroidRuntime(321):  at android.view.View.performClick(View.java:2344)

E/AndroidRuntime(321):  at android.view.View.onTouchEvent(View.java:4133)

E/AndroidRuntime(321):  at android.widget.TextView.onTouchEvent(TextView.java:6510)

E/AndroidRuntime(321):  at android.view.View.dispatchTouchEvent(View.java:3672)

E/AndroidRuntime(321):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882)

E/AndroidRuntime(321):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882)

E/AndroidRuntime(321):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882)

E/AndroidRuntime(321):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882)

E/AndroidRuntime(321):  at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1712)

E/AndroidRuntime(321):  at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1202)

E/AndroidRuntime(321):  at android.app.Activity.dispatchTouchEvent(Activity.java:1987)

E/AndroidRuntime(321):  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1696)

E/AndroidRuntime(321):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1658)

E/AndroidRuntime(321):  at android.os.Handler.dispatchMessage(Handler.java:99)

E/AndroidRuntime(321):  at android.os.Looper.loop(Looper.java:123)

E/AndroidRuntime(321):  at android.app.ActivityThread.main(ActivityThread.java:4203)

E/AndroidRuntime(321):  at java.lang.reflect.Method.invokeNative(Native Method)

E/AndroidRuntime(321):  at java.lang.reflect.Method.invoke(Method.java:521)

E/AndroidRuntime(321):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)

E/AndroidRuntime(321):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549)

E/AndroidRuntime(321):  at dalvik.system.NativeStart.main(Native Method)

The if … else works correctly.
Have you got any ideas? Please help me.

Answer 1

You just need to do a check on what the user has typed:

String input = editText.getText().toString();

if(input == null || input.trim().equals("")){
      Toast.makeText(context, "Sorry you did't type anything"), Toast.LENGTH_SHORT).show();
}

EDIT

If you have a float, you have to do the check before you parse the float:

String input = editText.getText().toString();

if(input == null || input.trim().equals("")){
      // Toast message
      return;
}
float num1 = Float.parseFloat(input);

or

try{

   float num1 = Float.parseFloat(numA.getText().toString());

} catch (NumberFormatException e) {
   // Toast message - you cannot get a float from that input
   return;
}