android8.1

### oefening 1 ###

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TableLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent" >

            <EditText
                android:id="@+id/txtNumber1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" />

        </TableRow>

        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent" >

            <EditText
                android:id="@+id/txtNumber2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" />

        </TableRow>

        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent" >

            <Button
                android:id="@+id/btnAdd"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="optellen" />

            <TextView
                android:id="@+id/txtResult1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" />
        </TableRow>

    </TableLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

Download hier het bestand.

### oefening 2 ###

public class MainActivity extends AppCompatActivity {

    EditText firstNumber;
    EditText secondNumber;
    TextView addResult;
    Button btnAdd;
    double num1, num2, sum;

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

        firstNumber = (EditText)findViewById(R.id.txtNumber1);
        secondNumber = (EditText)findViewById(R.id.txtNumber2);
        addResult = (TextView)findViewById(R.id.txtResult1);
        btnAdd = (Button)findViewById(R.id.btnAdd);

        btnAdd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {

                    num1 = Double.parseDouble(firstNumber.getText().toString());
                    num2 = Double.parseDouble(secondNumber.getText().toString());
                    sum = num1 + num2;

                    addResult.setText(Double.toString(sum));

                    } catch (Exception e) {

                        addResult.setText(e.getMessage());

                    }
            }
        });
    }

}

Download hier het bestand.

### oefening 3 ###

btnAdd.setOnClickListener(new View.OnClickListener() {
        
        ...

        } catch (Exception e) {
            if (e instanceof NumberFormatException) {
                addResult.setText("Geen tekst a.u.b.");
            } else {
                addResult.setText(e.getMessage());
            }
        }

        ...
    }
});

Download hier het bestand.