后退按钮无响应

Question

我似乎不明白为什么此活动中的后退按钮不起作用。请问该如何解决此问题？我尝试了其他一些解决方案，但大多数似乎不起作用？我希望用户返回按下按钮后，进入MainActivity。

我已经添加了家长活动的名称。你们有什么建议吗？

public class WaterSelectionActivity extends AppCompatActivity {
//Firebase Auth for Userlocation
private FirebaseAuth mAuth;
String currentUser;
DatabaseReference mgetUsername;
final ArrayList<String> selection = new ArrayList<>();
final ArrayList<String> pickedNumber = new ArrayList<>();
Switch simpleSwitch;
ActionBar actionBar;
ScrollableNumberPicker numberPicker1;
CheckBox checkbox1;
CheckBox checkbox2;
ImageView mimgop;
ImageView mimageViewop;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_water_selection);
    mAuth = FirebaseAuth.getInstance();
    currentUser = mAuth.getCurrentUser().getUid();
    mgetUsername = FirebaseDatabase.getInstance().getReference().child("Users").child(currentUser);
    simpleSwitch = (Switch) findViewById(R.id.switch2);
    mimageViewop = (ImageView) findViewById(R.id.imageViewop);
    mimageViewop.animate().alpha(1f).setDuration(2000);
    mimgop = (ImageView) findViewById(R.id.imgop);
    mimageViewop.animate().alpha(1f).setDuration(3000);
    checkbox1 = (CheckBox) findViewById(R.id.checkBox);
    checkbox2 = (CheckBox) findViewById(R.id.secondCheckbox);
    numberPicker1 = (ScrollableNumberPicker) findViewById(R.id.number_picker_horizontal);
    numberPicker1.setMaxValue(10);
    numberPicker1.setMinValue(3);
    numberPicker1.setListener(new ScrollableNumberPickerListener() {
        @Override
        public void onNumberPicked(int value) {
            // Do some magic
            pickedNumber.add(String.valueOf(value));
        }
    });
    actionBar = getSupportActionBar();
    actionBar.setBackgroundDrawable(new ColorDrawable(Color.parseColor("#FF8C00")));
    actionBar.setTitle("Water Specifics");
    //set the current state of a Switch
    simpleSwitch.setBackgroundColor(Color.parseColor("#FF8C00"));
    simpleSwitch.setChecked(false);
}

public void selectItem(View view) {
    boolean checked = ((CheckBox) view).isChecked();
    if (view.getId() == R.id.checkBox) {
        if (checked) {
            selection.add("15ltr");
            checkbox2.setVisibility(View.INVISIBLE);
        } else {
            selection.remove("15ltr");
            checkbox2.setVisibility(View.VISIBLE);
        }
    } else {
        if (checked) {
            selection.add("2000ltr");
            checkbox1.setVisibility(View.INVISIBLE);
        } else {
            selection.remove("2000ltr");
            checkbox1.setVisibility(View.VISIBLE);
        }
    }
}

public void submitWater(View view) {
    //Getting the switch value
    String statusSwitch1 = "";
    if (simpleSwitch.isChecked()) {
        statusSwitch1 = statusSwitch1 + "Fresh Water";
    } else {
        statusSwitch1 = statusSwitch1 + "Regular Salty Water";
    }
    Toast.makeText(this, statusSwitch1, Toast.LENGTH_SHORT).show();
    String finalSelection = "";
    for (String Selections : selection) {
        finalSelection = finalSelection + selection + "\n";
    }
    Toast.makeText(this, finalSelection, Toast.LENGTH_SHORT).show();
    final String finalStatusSwitch = statusSwitch1;
    final String finalSelection1 = finalSelection;
    numberPicker1.setListener(new ScrollableNumberPickerListener() {
        @Override
        public void onNumberPicked(int value) {
            // Do some magic
            pickedNumber.add(String.valueOf(value));
        }
    });
    Toast.makeText(WaterSelectionActivity.this, pickedNumber.toString(), Toast.LENGTH_SHORT).show();
    final String finalStatusSwitch1 = statusSwitch1;
    final String finalSelection2 = finalSelection;
    mgetUsername.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            //Values
            String name = dataSnapshot.child("name").getValue().toString();
            String waterType = finalStatusSwitch1;
            String container = finalSelection2;
            String quantity = pickedNumber.toString();
            //Put these values in an intent and send them to the next page
        }
        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    });
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    return onKey(keyCode, event);
}
@Override
public boolean onKeyUp(int keyCode, KeyEvent event) {
    return onKey(keyCode, event);
}
private boolean onKey(int keyCode, KeyEvent event) {
    if (numberPicker1.isFocused()) {
        return numberPicker1.handleKeyEvent(keyCode, event);
    }
    return false;
}

}