我有一个闹钟应用程序，当在主活动中使用“后退”按钮时，我刚刚添加了代码以退出程序。但是，当我这样做时，用户执行的最后一个操作将被撤消。例如，如果用户创建了三个警报，然后按后退按钮，则只会显示两个警报。
这是“主要活动”中的“后退”按钮代码：
@Override
public void onBackPressed() {
moveTaskToBack(true);
android.os.Process.killProcess(android.os.Process.myPid());
System.exit(1);
}
以防万一，这是我正在测试的两个活动中的所有代码：
MainActivity.java（故意具有此后退按钮功能的唯一活动）
public class MainActivity extends AppCompatActivity {
ListView alarmListView;
ArrayList<Alarm> alarmList = new ArrayList<Alarm>();
AlarmAdapter alarmAdapter;
String filename = "alarmList";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
alarmListView = findViewById(R.id.alarmListView);
// Credit to Mitch Woodbright for helping with this section, and other try/catch blocks.
try
{
ArrayList<Alarm> alarm = (ArrayList<Alarm>) getIntent().getSerializableExtra("alarmList");
for(Alarm elements : alarm){
alarmList.add(elements);
}
writeAlarmList(alarmList);
}
catch (NullPointerException e){
System.out.println("AlarmList is empty.");
}
try {
alarmList = readAlarmList();
}
catch (NullPointerException e) {
}
alarmAdapter = new AlarmAdapter(MainActivity.this, alarmList){
@Override
public void onUpdateClick(int position, ArrayList<Alarm> alarmList) {
super.onUpdateClick(position, alarmList);
Intent updateAlarmIntent = new Intent(MainActivity.this,
CreateAlarmActivity.class);
updateAlarmIntent.putExtra("alarmList", alarmList);
updateAlarmIntent.putExtra("position", position);
startActivity(updateAlarmIntent);
}
};
alarmListView.setAdapter(alarmAdapter);
alarmAdapter.notifyDataSetChanged();
alarmListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Intent updateAlarmIntent = new Intent(MainActivity.this, CreateAlarmActivity.class);
updateAlarmIntent.putExtra("alarmList", alarmList);
updateAlarmIntent.putExtra("position", position);
startActivity(updateAlarmIntent);
}
});
// writeAlarmList(alarmList);
}
protected void onStart() {
super.onStart();
alarmList = readAlarmList();
}
protected void onResume() {
super.onResume();
alarmList = readAlarmList();
}
protected void onPause() {
super.onPause();
writeAlarmList(alarmList);
}
protected void onStop() {
super.onStop();
writeAlarmList(alarmList);
}
@Override
public void onBackPressed() {
// Thanks to Mitch for this line.
moveTaskToBack(true);
android.os.Process.killProcess(android.os.Process.myPid());
System.exit(1);
}
// Create alarm when user presses FAB on activity_main.xml.
public void createNewAlarm(View view) {
Intent createAlarmIntent = new Intent(this, CreateAlarmActivity.class);
createAlarmIntent.putExtra("alarmList", alarmList);
startActivity(createAlarmIntent);
}
public void testAlarmActivated(View view){
//Intent activateAlarmIntent = new Intent(this, AlarmActivatedActivity.class);
//startActivity(activateAlarmIntent);
while(alarmList.size() > 0){
alarmList.remove(0);
}
Intent deleteEverythingIntent = new Intent(MainActivity.this, MainActivity.class);
deleteEverythingIntent.putExtra("alarmList", alarmList);
startActivity(deleteEverythingIntent);
}
public void writeAlarmList(ArrayList<Alarm> alarmList){
try {
FileOutputStream fos = openFileOutput(filename, Context.MODE_PRIVATE);
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(alarmList);
oos.close();
}
catch (FileNotFoundException e){
e.printStackTrace();
}
catch (IOException e) {
e.printStackTrace();
}
}
public ArrayList<Alarm> readAlarmList(){
try {
FileInputStream fis = openFileInput(filename);
ObjectInputStream ois = new ObjectInputStream(fis);
ArrayList<Alarm> alarmList = (ArrayList<Alarm>) ois.readObject();
ois.close();
return alarmList;
}
catch (FileNotFoundException e) {
ArrayList<Alarm> alarmList = new ArrayList<Alarm>();
System.out.println("File not found. Making empty list.");
return alarmList;
}
catch (IOException e) {
e.printStackTrace();
}
catch (ClassNotFoundException e) {
e.printStackTrace();
}
catch (NullPointerException e) {
ArrayList<Alarm> alarmList = new ArrayList<Alarm>();
System.out.println("Null pointer exception. Making empty list.");
return alarmList;
}
ArrayList<Alarm> alarmList = new ArrayList<Alarm>();
return alarmList;
}
}
CreateAlarmActivity.java（用于创建/更新/删除警报的活动）
public class CreateAlarmActivity extends AppCompatActivity {
// If the alarm is being created, position = -1.
int position = -1;
int alarmHour;
int alarmMinute;
boolean isPm;
int snoozeTimer;
int[] daysActive;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_create_alarm);
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
alarmList = (ArrayList<Alarm>)getIntent().getSerializableExtra("alarmList");
try {
// If we're updating an alarm, return the position of the alarm to update.
position = (int)getIntent().getSerializableExtra("position");
}
// Else, keep going.
catch (NullPointerException e){
}
Button hourButton = findViewById(R.id.buttonHours);
Button minuteButton = findViewById(R.id.buttonMinutes);
Button isPmButton = findViewById(R.id.buttonAmPm);
Button snoozeTimerButton = findViewById(R.id.buttonSnoozeTimer);
Button sundayButton = findViewById(R.id.buttonSunday);
Button mondayButton = findViewById(R.id.buttonMonday);
Button tuesdayButton = findViewById(R.id.buttonTuesday);
Button wednesdayButton = findViewById(R.id.buttonWednesday);
Button thursdayButton = findViewById(R.id.buttonThursday);
Button fridayButton = findViewById(R.id.buttonFriday);
Button saturdayButton = findViewById(R.id.buttonSaturday);
// If creating a new alarm, initialise data as default.
if (position == -1){
alarmHour = 6;
alarmMinute = 0;
isPm = false;
snoozeTimer = 10;
daysActive = new int[] {0, 0, 0, 0, 0, 0, 0};
}
// If updating an alarm, grab the defaults we already had.
else {
Alarm tempAlarm = alarmList.get(position);
alarmHour = tempAlarm.hour;
alarmMinute = tempAlarm.minute;
isPm = tempAlarm.isPm;
snoozeTimer = tempAlarm.snoozeTimer;
daysActive = tempAlarm.daysActive;
}
// Set buttons to what they should be.
hourButton.setText(Integer.toString(alarmHour));
snoozeTimerButton.setText(Integer.toString(snoozeTimer));
if (alarmMinute < 10){
minuteButton.setText("0" + Integer.toString(alarmMinute));
}
else {
minuteButton.setText(Integer.toString(alarmMinute));
}
if (!isPm){
isPmButton.setText("am");
}
else {
isPmButton.setText("pm");
}
setDayColor(sundayButton, daysActive[0]);
setDayColor(mondayButton, daysActive[1]);
setDayColor(tuesdayButton, daysActive[2]);
setDayColor(wednesdayButton, daysActive[3]);
setDayColor(thursdayButton, daysActive[4]);
setDayColor(fridayButton, daysActive[5]);
setDayColor(saturdayButton, daysActive[6]);
}
ArrayList<Alarm> alarmList = new ArrayList<Alarm>();
// Add one to the hour of the alarm.
public void changeHour(View view) {
Button btn = findViewById(R.id.buttonHours);
if (alarmHour == 12){
alarmHour = 0;
}
else {
alarmHour++;
}
btn.setText(Integer.toString(alarmHour));
}
// Add one to the minute of the alarm.
public void changeMinute(View view) {
Button btn = findViewById(R.id.buttonMinutes);
if (alarmMinute == 59) {
alarmMinute = 0;
}
else {
alarmMinute++;
}
if (alarmMinute < 10) {
// Ensure minute 1 becomes 01, e.g, 6:01 am.
btn.setText("0" + Integer.toString(alarmMinute));
}
else {
btn.setText(Integer.toString(alarmMinute));
}
}
public void changeAmPm(View view) {
Button btn = findViewById(R.id.buttonAmPm);
if (isPm == true) {
isPm = false;
btn.setText("am");
}
else {
isPm = true;
btn.setText("pm");
}
}
public void changeSnoozeTimer(View view) {
Button btn = findViewById(R.id.buttonSnoozeTimer);
if (snoozeTimer == 15){
snoozeTimer = 1;
}
else {
snoozeTimer++;
}
btn.setText(Integer.toString(snoozeTimer));
}
public void finishAlarm(View view){
EditText alarmName = findViewById(R.id.alarmName);
String name = alarmName.getText().toString();
Alarm alarm = new Alarm(name, alarmHour, alarmMinute, isPm, daysActive, snoozeTimer);
// If we're creating an alarm.
if (position == -1) {
try {
alarmList.add(alarm);
} catch (Exception e) {
}
}
// Else, we're updating one.
else {
try {
// Set the alarm we're updating to the new alarm.
alarmList.set(position, alarm);
} catch (Exception e) {
}
}
Intent finishAlarmIntent = new Intent(this, MainActivity.class);
finishAlarmIntent.putExtra("alarmList", alarmList);
startActivity(finishAlarmIntent);
}
public void cancelAlarm(View view){
Intent cancelAlarmIntent = new Intent(this, MainActivity.class);
cancelAlarmIntent.putExtra("alarmList", alarmList);
startActivity(cancelAlarmIntent);
}
public void deleteAlarm(View view) {
// If creating a new alarm, deleting is the same as cancelling.
if (position == -1) {
Intent cancelAlarmIntent = new Intent(this, MainActivity.class);
cancelAlarmIntent.putExtra("alarmList", alarmList);
startActivity(cancelAlarmIntent);
}
else {
// Remove the alarm.
alarmList.remove(position);
Intent cancelAlarmIntent = new Intent(this, MainActivity.class);
cancelAlarmIntent.putExtra("alarmList", alarmList);
startActivity(cancelAlarmIntent);
}
}
public void changeSunday(View view) {
Button btn = findViewById(R.id.buttonSunday);
daysActive[0] = switchDay(daysActive[0]);
setDayColor(btn, daysActive[0]);
}
public void changeMonday(View view) {
Button btn = findViewById(R.id.buttonMonday);
daysActive[1] = switchDay(daysActive[1]);
setDayColor(btn, daysActive[1]);
}
public void changeTuesday(View view) {
Button btn = findViewById(R.id.buttonTuesday);
daysActive[2] = switchDay(daysActive[2]);
setDayColor(btn, daysActive[2]);
}
public void changeWednesday(View view) {
Button btn = findViewById(R.id.buttonWednesday);
daysActive[3] = switchDay(daysActive[3]);
setDayColor(btn, daysActive[3]);
}
public void changeThursday(View view) {
Button btn = findViewById(R.id.buttonThursday);
daysActive[4] = switchDay(daysActive[4]);
setDayColor(btn, daysActive[4]);
}
public void changeFriday(View view) {
Button btn = findViewById(R.id.buttonFriday);
daysActive[5] = switchDay(daysActive[5]);
setDayColor(btn, daysActive[5]);
}
public void changeSaturday(View view) {
Button btn = findViewById(R.id.buttonSaturday);
daysActive[6] = switchDay(daysActive[6]);
setDayColor(btn, daysActive[6]);
}
// Helper method to switch the daysActive from 0 to 1 or from 1 to 0.
public int switchDay(int day) {
if (day == 0){
return 1;
}
return 0;
}
// Helper method to set the color of a daysActive button when updating the alarm.
public void setDayColor(Button btn, int day) {
if (day == 1) {
// Source: https://stackoverflow.com/questions/2173936/how-to-set-background-color-of-a-view
// Credit goes to EddieB for the below line.
btn.getBackground().setColorFilter(Color.parseColor("#00ff00"), PorterDuff.Mode.DARKEN);
} else {
// Source: https://stackoverflow.com/questions/14802354/how-to-reset-a-buttons-background-color-to-default
// Credit goes to Ivo for the below line.
btn.getBackground().clearColorFilter();
}
}
}
答案 0 :(得分：0)
面向未来的人：
我最终使用以下方法解决了这个问题：
@Override
public void onBackPressed() {
this.finishAffinity();
}