我的代码没有正确更改TextView

Question

Everything works with no errors, but in the xml, tvfinalgrade stays 0.0... Why isn't the double fin being displayed? I'm sure about what order the tvfin code lines should be written, but I'm assuming its not right.

public class GFActivity extends Activity {
public double fin;
 @Override
    public void onCreate(Bundle savedInstanceState) {          

        super.onCreate(savedInstanceState);    
        setContentView(R.layout.getfinal);

        double q1, q2, ex;
         EditText etq1, etq2, eteg;
         etq1 = (EditText)findViewById(R.id.editText1);
            try{
                q1 = Double.parseDouble(etq1.getText().toString());
            } catch (NumberFormatException e) {
                q1=0;
            }
         etq2 = (EditText)findViewById(R.id.editText2);
            try{
                q2 = Double.parseDouble(etq2.getText().toString());
            } catch (NumberFormatException e){
                q2 = 0;
            }
         eteg = (EditText)findViewById(R.id.editText3);
         try{
             ex = Double.parseDouble(eteg.getText().toString());
         } catch (NumberFormatException e){
             ex = 0;
         }
        fin = 0.4*q1+0.4*q2+0.2*ex;
            if(fin == (int)fin){
                System.out.println((int)fin);
            }
            else{
                fin = 0.01*((int)(fin*100));
                System.out.println(fin);
            } 
            Button solve = (Button)findViewById(R.id.getfinbutton);
            solve.setOnClickListener(new OnClickListener() {

                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    TextView tvfin= TextView)findViewById(R.id.tvfinalgrade);
                         tvfin.setText(fin+"");
                }
            });


    }
}

Answer 1

When you start the app, in the onCreate() you already parse the EditText content(which are empty, so you throw NumberFormatException and your fin variable ends up as 0 ) and when you get to the part of setting the result(the user clicks the Button ) you set the fin which is currently 0 to the TextView (the problem is that when the user clicks the Button you never get the current EditText content to do any calculation and the fin variable is the old value( 0 )). Move your calculation in the onClick() method:

Button solve = (Button)findViewById(R.id.getfinbutton);
            solve.setOnClickListener(new OnClickListener() {

                public void onClick(View v) {
                   double q1, q2, ex;
         EditText etq1, etq2, eteg;
         etq1 = (EditText)findViewById(R.id.editText1);
            try{
                q1 = Double.parseDouble(etq1.getText().toString());
            } catch (NumberFormatException e) {
                q1=0;
            }
         etq2 = (EditText)findViewById(R.id.editText2);
            try{
                q2 = Double.parseDouble(etq2.getText().toString());
            } catch (NumberFormatException e){
                q2 = 0;
            }
         eteg = (EditText)findViewById(R.id.editText3);
         try{
             ex = Double.parseDouble(eteg.getText().toString());
         } catch (NumberFormatException e){
             ex = 0;
         }
        fin = 0.4*q1+0.4*q2+0.2*ex;
            if(fin == (int)fin){
                System.out.println((int)fin);
            }
            else{
                fin = 0.01*((int)(fin*100));
                System.out.println(fin);
            } 
                    TextView tvfin= TextView)findViewById(R.id.tvfinalgrade);
                         tvfin.setText(fin+"");
                }
            });