Android：java.lang.IllegalStateException：已经附加

Question

我正在开发一个Android应用程序，用于在SQLite数据库中存储个人信息，将其撤出并在Activity中显示列表。实际上，当用户将数据放入数据库并返回到Activity时，必须刷新页面才能升级包含新数据的列表。我使用语句onCreate(null)来创建它，但是出现了一个例外：java.lang.IllegalStateException: Already attached。

以下是代码：

/* MainActivity */
public class MainActivity
        extends AppCompatActivity
        implements View.OnClickListener{

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
            if(requestCode==0x1&&resultCode==RESULT_OK){
                onCreate(null); // Upgrade the list
            }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button addItem=(Button)findViewById(R.id.addItem);
        addItem.setOnClickListener(this);
        .....
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.addItem:
                Intent intent=new Intent(this,AddItemActivity.class);
                startActivityForResult(intent,0x1);
                break;
            default:
                break;
        }
    }
}

/*AddItemActivity*/
public class AddItemActivity
        extends AppCompatActivity
        implements View.OnClickListener{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_item);
        Button submit=(Button)findViewById(R.id.submit);//get submit button
        submit.setOnClickListener(this);
        ....
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.submit:
                EditText editName=(EditText)findViewById(R.id.editName),
                         editAge=(EditText)findViewById(R.id.editAge);
                         insert(new Person(
                                        editName.getText().toString(),
                                        Integer.parseInt(editAge.getText().toString())));
                //return 
                setResult(RESULT_OK,null);
                finish();
                break;
            default:
                break;
        }
    }
}

stackTrace是这样的：

 java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=-1, data=null} to activity {com.example.sqlitetest/com.example.sqlitetest.MainActivity}: java.lang.IllegalStateException: Already attached
 at android.app.ActivityThread.deliverResults(ActivityThread.java:4053)
at android.app.ActivityThread.handleSendResult(ActivityThread.java:4096)
at android.app.ActivityThread.-wrap20(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1516)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.IllegalStateException: Already attached
at android.support.v4.app.FragmentManagerImpl.attachController(FragmentManager.java:2871)
at android.support.v4.app.FragmentController.attachHost(FragmentController.java:104)
at android.support.v4.app.FragmentActivity.onCreate(FragmentActivity.java:317)
at android.support.v7.app.AppCompatActivity.onCreate(AppCompatActivity.java:85)
at com.example.sqlitetest.MainActivity.onCreate(MainActivity.java:29)
at com.example.sqlitetest.MainActivity.onActivityResult(MainActivity.java:23)
at android.app.Activity.dispatchActivityResult(Activity.java:6915)