Question

我正在使用Parse.com在我的应用的第二个活动中填充ListView。单击ListView中的项目将打开第三个活动。问题是当使用向上按钮返回第二个活动时，ListView消失了。由于某些原因，使用“后退”按钮时不会发生此行为。此外，仅在第二个活动中使用普通查询时不会发生这种情况。关于query.whereEqualsTo（＆＃34; department＆＃34;，department）行的一些事情正在抛弃整个事情。

第1次活动：

public class MainActivity extends ActionBarActivity {

private Button mMEButton;
private Button mCEButton;

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

    mMEButton = (Button)findViewById(R.id.meButton);
    mCEButton = (Button)findViewById(R.id.ceButton);



    mMEButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, ProfessorsActivity.class);
            intent.putExtra("department", "ME");
            startActivity(intent);
        }
    });

    mCEButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, ProfessorsActivity.class);
            intent.putExtra("department", "CE");
            startActivity(intent);
        }
    });
}

第二项活动：

public class ProfessorsActivity extends ActionBarActivity {

private ParseQueryAdapter<ParseObject> adapter;

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

    Intent intent = getIntent();
    final String department = intent.getStringExtra("department");

    ParseQueryAdapter.QueryFactory<ParseObject> factory =
            new ParseQueryAdapter.QueryFactory<ParseObject>() {
                public ParseQuery create() {
                    ParseQuery query = new ParseQuery("Professor");
                    query.whereEqualTo("department", department);
                    return query;
                }
            };

    adapter = new ParseQueryAdapter<ParseObject>(this, factory) {
        @Override
        public View getItemView(ParseObject professor, View v, ViewGroup parent) {
            if (v == null) {
                v = View.inflate(getContext(), R.layout.professor_item, null);
            }
            TextView contentView = (TextView) v.findViewById(R.id.professorNameTextView);
            contentView.setText(professor.getString("lastName") + ", " + professor.getString("firstName"));
            return v;
        }
    };
    //adapter.setTextKey("lastName");
    ListView listView = (ListView) findViewById(R.id.listView);
    listView.setAdapter(adapter);

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

            final ParseObject tappedProfessor = adapter.getItem(position);
            String professorId = tappedProfessor.getObjectId();

            Intent intent = new Intent(ProfessorsActivity.this, OfficeHoursActivity.class);
            intent.putExtra("professorId", professorId);
            startActivity(intent);
        }
    });
}

第3次活动：

public class OfficeHoursActivity extends ActionBarActivity {

private TextView mNameTextView;
private TextView mTimeTextView1;
private TextView mDaysTextView1;
private TextView mTimeTextView2;
private TextView mDaysTextView2;

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

    Intent intent = getIntent();
    String professorId = intent.getStringExtra("professorId");

    mNameTextView = (TextView) findViewById(R.id.professorName);
    mTimeTextView1 = (TextView) findViewById(R.id.officeHourTime1);
    mDaysTextView1 = (TextView) findViewById(R.id.officeHourDays1);
    mTimeTextView2 = (TextView) findViewById(R.id.officeHourTime2);
    mDaysTextView2 = (TextView) findViewById(R.id.officeHourDays2);


    mNameTextView.setVisibility(INVISIBLE);
    mTimeTextView1.setVisibility(INVISIBLE);
    mDaysTextView1.setVisibility(INVISIBLE);
    mTimeTextView2.setVisibility(INVISIBLE);
    mDaysTextView2.setVisibility(INVISIBLE);


    ParseQuery<ParseObject> query = ParseQuery.getQuery("Professor");

    // Retrieve the object by id
    query.getInBackground(professorId, new GetCallback<ParseObject>() {
        public void done(ParseObject currentProfessor, ParseException e) {
            if (e == null) {
                mNameTextView.setText(currentProfessor.getString("lastName") + ", " + currentProfessor.getString("firstName"));
                mTimeTextView1.setText(currentProfessor.getString("start1") + " - " + currentProfessor.getString("end1"));
                mDaysTextView1.setText(currentProfessor.getString("days1"));

                mNameTextView.setVisibility(VISIBLE);
                mTimeTextView1.setVisibility(VISIBLE);
                mDaysTextView1.setVisibility(VISIBLE);

                if (currentProfessor.getString("start2") != null) {
                    mTimeTextView2.setText(currentProfessor.getString("start2") + " - " + currentProfessor.getString("end2"));
                    mDaysTextView2.setText(currentProfessor.getString("days2"));

                    mTimeTextView2.setVisibility(VISIBLE);
                    mDaysTextView2.setVisibility(VISIBLE);
                }
            } else {
                //something went wrong
            }
        }
    });

Answer 1

默认情况下，向上按钮会创建父活动的新实例。如果你想让它表现为后退按钮只是覆盖＆＃34; onOptionsItemSelected＆＃34; in＆＃34; OfficeHoursActivity＆＃34;并执行以下操作：

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    if(item.getItemId() == android.R.id.home) {
        onBackPressed();
        return true;
    }

    return super.onOptionsItemSelected(item);
}

Answer 2

private void ListView(){
ParseQueryAdapter.QueryFactory<ParseObject> factory =
            new ParseQueryAdapter.QueryFactory<ParseObject>() {
                public ParseQuery create() {
                    ParseQuery query = new ParseQuery("Professor");
                    query.whereEqualTo("department", department);
                    return query;
                }
            };

    adapter = new ParseQueryAdapter<ParseObject>(this, factory) {
        @Override
        public View getItemView(ParseObject professor, View v, ViewGroup parent) {
            if (v == null) {
                v = View.inflate(getContext(), R.layout.professor_item, null);
            }
            TextView contentView = (TextView) v.findViewById(R.id.professorNameTextView);
            contentView.setText(professor.getString("lastName") + ", " + professor.getString("firstName"));
            return v;
        }
    };
    //adapter.setTextKey("lastName");
    ListView listView = (ListView) findViewById(R.id.listView);
    listView.setAdapter(adapter);
}

现在从onResume（）调用此方法。不要从onCreate（）调用它。

@Override
public void onResume(){
    super.onResume();
    ListView();

}

现在检查..可能是你的问题会解决.. !!!

Answer 3

我通过将以下标记添加到AndroidManifest.xml文件中的第二个活动来解决了这个问题。

android:launchMode="singleTop"

这可以防止“向上”按钮在单击时重新创建活动。

单击向上按钮后返回活动时ListView消失

3 个答案: