java - 在 Activity 不正常之间传递数据

我在一个简单的应用程序中有以下情形：
1-用户单击MainActivity上的菜单按钮以在整个新屏幕上打开另一个活动：addTimeActivity，他们可以在其中输入注释及其时间。
2-新活动具有两个编辑文本：时间和便笺，用户输入数据然后单击保存，或者在不想保存便笺时可以单击取消按钮。
3- addTimeActiviy通过意图传递数据。
4-addTimeActivity完成。
5-应该将数据保存在适配器中，该适配器又将其显示为MainActivity上的列表，TimeTrackerAdapter中的addTimeRecord方法将String数据添加到时间ArrayList中。
现在，单击“保存”按钮时，将出现NullPointerException。

这是MainActivity：

public class MainActivity extends ActionBarActivity {

ListView listView;
TimeTrackerAdapter timeTrackerAdapter;
public static final int TIME_ENTRY_REQUEST_CODE=1;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    timeTrackerAdapter=new TimeTrackerAdapter();
     listView=(ListView) findViewById(R.id.recordList);
    listView.setAdapter(timeTrackerAdapter);
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    super.onCreateOptionsMenu(menu);
    MenuInflater menuInflater=getMenuInflater();
    menuInflater.inflate(R.menu.menu_list_item, menu);
    return true;
}
protected void onActivityResult(int requestCode,int resultCode,Intent data)
{
    if(requestCode==TIME_ENTRY_REQUEST_CODE)
        {
        if(resultCode==RESULT_OK)
        {
        Bundle extras=getIntent().getExtras();
        String time=extras.getString("time");
        String notes=extras.getString("notes");
        timeTrackerAdapter.addTimeRecord(time, notes);
        timeTrackerAdapter.notifyDataSetChanged();
        }
    }
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
   if(item.getItemId()==R.id.add_time_menu_item)
   {
       Intent intent=new Intent(getApplicationContext(),AddTimeActivity.class);
       startActivityForResult(intent,TIME_ENTRY_REQUEST_CODE);
       return true;
   }
    return super.onOptionsItemSelected(item);
} }

这是addTimeActivity：

public class AddTimeActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.add_time);
}
public void onCancel(View view)
{
    finish();
}
public void onSave(View view)
{
    Intent intent = new Intent(AddTimeActivity.this,MainActivity.class);
    EditText editTextNotes=(EditText) findViewById(R.id.notes_edit_text);
    intent.putExtra("notes",editTextNotes.getText().toString());
    EditText editTextTime=(EditText) findViewById(R.id.time_edit_text);
    intent.putExtra("time", editTextTime.getText().toString());
    this.setResult(RESULT_OK,intent);
    startActivity(intent);
    finish();

}
}

适配器：

public class TimeTrackerAdapter extends BaseAdapter{

ArrayList<TimeRecord> times=new ArrayList<TimeRecord>();
TextView timeView,noteView;
@Override
public int getCount() {
    // TODO Auto-generated method stub
    return times.size();
}
public TimeTrackerAdapter()
{
}

@Override
public Object getItem(int index) {
    // TODO Auto-generated method stub
    return getItem(index);
}

@Override
public long getItemId(int index) {
    // TODO Auto-generated method stub
    return index;
}

public void addTimeRecord(String time,String notes)
{
    TimeRecord timeRecord=new TimeRecord(time,notes);
    times.add(timeRecord);
}
@Override
public View getView(int index, View view, ViewGroup parent) {
    // TODO Auto-generated method stub
    if(view==null)
    {
        LayoutInflater inflater=LayoutInflater.from(parent.getContext());
        view=inflater.inflate(R.layout.time_tracker, parent,false);
    }
    TimeRecord time=times.get(index);
    TextView timeText=(TextView) view.findViewById(R.id.timeText);
    timeText.setText(time.getTime());
    TextView noteText=(TextView) view.findViewById(R.id.noteText);
    noteText.setText(time.getNote());
    return view;
}
}

最佳答案

您没有初始化成员变量timeTrackerAdapter！在您的onCreate中执行此操作，但应为TimeTrackerAdapter timeTrackerAdapter=new TimeTrackerAdapter();

同样，您在onActivityResult中使用了错误的意图。应该是这样的：

protected void onActivityResult(int requestCode,int resultCode,Intent data) // Intent data is the intent that includes the data of your AddTimeActivity
{
  if(requestCode==TIME_ENTRY_REQUEST_CODE)
  {
    if(resultCode==RESULT_OK)
    {
      Bundle extras=data.getExtras(); // not getIntent().getExtras()
      String time=extras.getString("time");
      String notes=extras.getString("notes");
      timeTrackerAdapter.addTimeRecord(time, notes);
      timeTrackerAdapter.notifyDataSetChanged();
    }
  }
}