我正在开发一个简单的应用程序，它将一个parcelable从一个活动传递到另一个活动。在MainActivity中，我有一个LinkedList，用于保存从parcelable获取的信息。但是，每次返回MainActivity时，都会删除先前存储在LinkedList（Parcelable）中的Object。我究竟做错了什么？在过去的3天里，我一直在努力弄清楚为什么它不能保存任何东西，但逻辑看起来很稳固。所以我更新了使用startActivityForResult，现在MainActivity中的Parcelable为NULL。
public class MainActivity extends Activity {
int tasks;
final static String TASK_KEY = "newTask";
final static String INDEX_KEY = "LLIndex";
Task t;
ScrollView scrollView;
LinearLayout taskHolder;
LinkedList<Task> taskList = new LinkedList<Task>();
@Override
protected void onCreate(Bundle savedInstanceState) {
Log.d("In onCreate", "here");
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView tvCounter = (TextView) findViewById(R.id.textView1);
taskHolder = (LinearLayout) findViewById(R.id.linearScroll);
//Checks for parcelable
if(getIntent().hasExtra(Create.TASK_KEY)){
Log.d("Task", "You've got mail!");
Task t = (Task)getIntent().getExtras().getParcelable(Create.TASK_KEY);
taskList.add(t);
addNewTask(t);
}
Log.d("LL size", Integer.toString(tasks));
tasks = taskList.size();
tvCounter.setText(Integer.toString(tasks) + " " + getApplicationContext().getResources().getString(R.string.tv_task));
Button plusButton = (Button) findViewById(R.id.button1);
plusButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent i = new Intent(MainActivity.this, Create.class);
startActivity(i);
}
});
}
void addNewTask(Task t) {
tasks++;
Log.d("In addNewTask method", t.toString());
LinearLayout newTaskLayout = new LinearLayout(getApplicationContext());
newTaskLayout.setOrientation(LinearLayout.VERTICAL);
LayoutParams params = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
newTaskLayout.setLayoutParams(params);
//int bottom = (int) getResources().getDimension(R.dimen.margin_bottom);
//int left = (int) getResources().getDimension(R.dimen.margin_left);
//params.setMargins(left, 0, 0, bottom);
TextView tvTitle = new TextView(getApplicationContext());
TextView tvDate = new TextView(getApplicationContext());
TextView tvTime = new TextView(getApplicationContext());
tvTitle.setTextColor(Color.BLACK);
tvDate.setTextColor(Color.BLACK);
tvTime.setTextColor(Color.BLACK);
tvTitle.setTypeface(tvTitle.getTypeface(), Typeface.BOLD);
tvTitle.setText(t.getName());
tvDate.setText(t.getDate());
tvTime.setText(t.getTime());
newTaskLayout.addView(tvTitle);
newTaskLayout.addView(tvDate);
newTaskLayout.addView(tvTime);
//params = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
//params.setMargins(0, 0, 0, 0);
//tvDate.setLayoutParams(params);
//tvTime.setLayoutParams(params);
//tvTitle.setTextSize(getResources().getDimension(R.dimen.size_of_text));
taskHolder.addView(newTaskLayout);
final int index = ((ViewGroup) newTaskLayout.getParent()).indexOfChild(newTaskLayout);
newTaskLayout.setOnClickListener(new View.OnClickListener() {//bind listener
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent i = new Intent(MainActivity.this,Display.class);
i.putExtra(TASK_KEY, taskList.get(index));
i.putExtra(INDEX_KEY, index);
startActivity(i);
}
});
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
Log.d("CheckStartActivity","onActivityResult and resultCode = "+resultCode);
// TODO Auto-generated method stub
super.onActivityResult(requestCode, resultCode, data);
if(resultCode==1){
Toast.makeText(this, "Pass", Toast.LENGTH_LONG).show();
Log.d("Task", "You've got mail!");
if(getIntent().hasExtra(Create.TASK_KEY)){
Task t = (Task)getIntent().getExtras().getParcelable(Create.TASK_KEY);
taskList.add(t);
addNewTask(t);
}
Log.d("LL size", Integer.toString(tasks));
tasks = taskList.size();
tvCounter.setText(Integer.toString(tasks) + " " + getApplicationContext().getResources().getString(R.string.tv_task));
}
else{
Toast.makeText(this, "Fail", Toast.LENGTH_LONG).show();
}
}
}
创建班级：
public class Create extends Activity{
private int year;
private int month;
private int day;
private String name, date, time, priority;
final static String TASK_KEY = "newTask";
static final int PICK_CONTACT_REQUEST = 1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_create);
final Calendar cal = Calendar.getInstance();
//Current Date
year = cal.get(Calendar.YEAR);
month = cal.get(Calendar.MONTH);
day = cal.get(Calendar.DAY_OF_MONTH);
final EditText etTitle = (EditText) findViewById(R.id.editText1);
final EditText etDate = (EditText) findViewById(R.id.editText2);
final EditText etTime = (EditText) findViewById(R.id.editText3);
final RadioGroup rg = (RadioGroup) findViewById(R.id.radioGroup1);
//int selectedId = rg.getCheckedRadioButtonId();
//final RadioButton radioSelected = (RadioButton) findViewById(selectedId);
Button save = (Button) findViewById(R.id.button1);
save.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//Get checked radio button
RadioButton rb = (RadioButton) findViewById(rg.getCheckedRadioButtonId());
// TODO Auto-generated method stub
name = etTitle.getText().toString();
date = etDate.getText().toString();
time = etTime.getText().toString();
priority = (String) rb.getTag();
Task t = new Task(name, date, time, priority);
Log.d("task", t.toString());
Intent i = new Intent(Create.this, MainActivity.class);
i.putExtra(TASK_KEY, t); //Puts new Task object into Intent to send
setResult(1,i);
finish();
}
});
etDate.setKeyListener(null);
etTime.setKeyListener(null);
final DatePickerDialog.OnDateSetListener datePick = new DatePickerDialog.OnDateSetListener() {
@Override
public void onDateSet(DatePicker view, int year, int monthOfYear,
int dayOfMonth) {
// TODO Auto-generated method stub
cal.set(Calendar.YEAR, year);
cal.set(Calendar.MONTH, monthOfYear);
cal.set(Calendar.DAY_OF_MONTH, dayOfMonth);
updateLabel();
}
private void updateLabel() {
// TODO Auto-generated method stub
String myFormat = "MM/dd/yy"; //In which you need put here
SimpleDateFormat sdf = new SimpleDateFormat(myFormat, Locale.US);
etDate.setText(sdf.format(cal.getTime()));
}
};
etDate.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
//Do whatever
new DatePickerDialog(Create.this, datePick, cal.get(Calendar.YEAR),
cal.get(Calendar.MONTH),
cal.get(Calendar.DAY_OF_MONTH)).show();
}
});
etTime.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Calendar curTime = Calendar.getInstance();
int hour = curTime.get(Calendar.HOUR_OF_DAY);
int minute = curTime.get(Calendar.MINUTE);
TimePickerDialog tp;
tp = new TimePickerDialog(Create.this, new TimePickerDialog.OnTimeSetListener() {
@Override
public void onTimeSet(TimePicker timePicker, int selectedHour, int selectedMinute) {
String am_pm;
String minuteStr;
Log.d("hour", Integer.toString(selectedHour));
if (selectedHour == 0){
selectedHour = 12;
am_pm = "AM";
}else if(selectedHour == 12){
selectedHour = 12;
am_pm = "PM";
}else if(selectedHour > 12) {
selectedHour -= 12;
am_pm = "PM";
}else{
am_pm = "AM";
}
if(selectedMinute < 10){
minuteStr = "0" + Integer.toString(selectedMinute);
}else{
minuteStr = Integer.toString(selectedMinute);
}
etTime.setText( selectedHour + ":" + minuteStr + " " + am_pm);
}
}, hour, minute, false);//Yes 24 hour time
tp.setTitle("Set Time");
tp.show();
}
});
}
}
答案 0 :(得分：0)
如果我正确理解了这个问题，那么您会在MainActivity中找到一条消息列表，并且您正在启动Create创建新消息的意图。然后，在保存时，您将开始一个新的MainActivity，并将新消息添加到列表中。
这种方法的问题是每次都会创建一个新的MainActivity实例，其中包含一个新的（空）LinkedList。
我会考虑使用startActivityForResult()来运行Create活动，并使用setResult()中的finish()和Create来返回新消息。
您还应该在'onSaveInstanceState'中保存列表内容，以处理MainActivity的破坏和重新创建（例如，当用户旋转设备时）。