Add Exchange button

.idea/vcs.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="" vcs="Git" />
+  </component>
+</project>
\ No newline at end of file

app/src/main/java/com/example/moneyconverter/MainActivity.java

@@ -8,6 +8,7 @@ import android.text.TextWatcher;
 import android.view.View;
 import android.widget.AdapterView;
 import android.widget.ArrayAdapter;
+import android.widget.Button;
 import android.widget.EditText;
 import android.widget.Spinner;
 
@@ -22,6 +23,7 @@ public class MainActivity extends AppCompatActivity {
     private EditText currencyBottom;
     private Spinner spinnerCurrencyTop;
     private Spinner spinnerCurrencyBottom;
+    private Button exchange;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
@@ -123,4 +125,14 @@ public class MainActivity extends AppCompatActivity {
             public void onNothingSelected(AdapterView<?> parent) { }
         });
     }
+
+    public void onClickExchange(View view) {
+        String top = currencyTop.getText().toString();
+        currencyTop.setText(currencyBottom.getText().toString());
+        currencyBottom.setText(top);
+
+        int topSpinner = (int) spinnerCurrencyTop.getSelectedItemId();
+        spinnerCurrencyTop.setSelection((int) spinnerCurrencyBottom.getSelectedItemId());
+        spinnerCurrencyBottom.setSelection(topSpinner);
+    }
 }

app/src/main/res/layout/activity_main.xml

@@ -50,4 +50,14 @@
         app:layout_constraintStart_toEndOf="@+id/currencyBottom"
         app:layout_constraintTop_toTopOf="@+id/currencyBottom" />
 
+    <Button
+        android:id="@+id/exchange"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Exchange"
+        android:onClick="onClickExchange"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintStart_toEndOf="@+id/coucou"
+        app:layout_constraintTop_toTopOf="parent" />
+
 </androidx.constraintlayout.widget.ConstraintLayout>
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