爲什麼我在將一個片段與另一個片段進行通信時將輸出變爲null？

Question

我，而在片段通信面臨的一個問題， 下面是我的代碼：

ListPolicies片段

public class ListPolicies extends ListFragment implements AdapterView.OnItemClickListener{ 


String polnames; 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 

    return inflater.inflate(R.layout.list_policies, null, false); 


} 

public String polName(String name){ 


    if(name!=null) { 
     polnames = name; 


    } 
    Log.d("Luffy", "Pos" +polnames); 
     return polnames; 

} 

    String polname = polName(polnames); 


@Override 
public void onActivityCreated(Bundle savedInstanceState) { 
    super.onActivityCreated(savedInstanceState); 
     if (polname != null) { 
      Log.d("Luffy", "Position 00"); 
      if (polname.equalsIgnoreCase("0")) { 
       Log.d("Luffy", "Position 0"); 
       ArrayAdapter adapter = ArrayAdapter.createFromResource(getActivity(), R.array.Engineering_Insurance, android.R.layout.simple_list_item_1); 
       setListAdapter(adapter); 
       getListView().setOnItemClickListener(this); 
      } 
     } 

} 
@Override 
public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 
    Toast.makeText(getActivity(), "Uploaded :" + position, Toast.LENGTH_LONG).show(); 
} 
} 

ViewPolicy片段

public class ViewPolicyFragment extends ListFragment implements AdapterView.OnItemClickListener{ 


String[] menutitles; 
TypedArray menuIcons; 

PolicyCommunicator comm; 

CustomAdapter adapter; 
private List<rowItem> rowItems; 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 

    return inflater.inflate(R.layout.view_policy_fragment, null, false); 
} 

@Override 
public void onActivityCreated(Bundle savedInstanceState) { 

    super.onActivityCreated(savedInstanceState); 

    menutitles = getResources().getStringArray(R.array.Insurance); 
    menuIcons = getResources().obtainTypedArray(R.array.icons); 

    rowItems = new ArrayList<rowItem>(); 

    for (int i = 0; i < menutitles.length; i++) { 
     rowItem items = new rowItem(menutitles[i], menuIcons.getResourceId(
       i, -1)); 

     rowItems.add(items); 
    } 

    adapter = new CustomAdapter(getActivity(), rowItems); 
    setListAdapter(adapter); 
    comm = (PolicyCommunicator) getActivity(); 
    getListView().setOnItemClickListener(this); 

} 

@Override 
public void onItemClick(AdapterView<?> parent, View view, int position, 
         long id) { 
    comm.policyName("" +position); 
    if(menutitles[position].equalsIgnoreCase("Engineering Insurance")){ 
     Toast.makeText(getActivity(), "You have Clicked on Engineering Insurance", Toast.LENGTH_SHORT) 
       .show(); 
    } 

    if(menutitles[position].equalsIgnoreCase("Fire Insurance")){ 
     Toast.makeText(getActivity(), "You have Clicked on Fire Insurance", Toast.LENGTH_SHORT) 
       .show(); 
    } 

    if(menutitles[position].equalsIgnoreCase("Liability Insurance")){ 
     Toast.makeText(getActivity(), "You have Clicked on Liability Insurance", Toast.LENGTH_SHORT) 
       .show(); 
    } 

} 



} 

和我的活動實現使方法

public class AfterLoginActivity extends AppCompatActivity implements PolicyCommunicator { 


Toolbar toolbar; 
FragmentManager manager; 
Intent intent= null, chooser= null; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.after_login_activity); 
    toolbar = (Toolbar) findViewById(R.id.app_bar); 
    setSupportActionBar(toolbar); 
    manager = getFragmentManager(); 
    AfterLoginAboutFragment fragViewPolicy = new AfterLoginAboutFragment(); 
    FragmentTransaction transaction = manager.beginTransaction(); 
    transaction.add(R.id.linearLayoutLoginFragment, fragViewPolicy, "View Policy"); 
    transaction.commit(); 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.menu_main, menu); 
    return true; 
} 

@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. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 
     return true; 
    } 

    return super.onOptionsItemSelected(item); 
} 


public void addLoginAboutFragment (View v){ 
    AfterLoginAboutFragment fragViewPolicy = new AfterLoginAboutFragment(); 
    FragmentTransaction transaction = manager.beginTransaction(); 
    transaction.replace(R.id.linearLayoutLoginFragment, fragViewPolicy, "View Policy"); 
    transaction.commit(); 

} 

public void addViewPolicyFragment (View v){ 
    ViewPolicyFragment fragViewPolicy = new ViewPolicyFragment(); 
    FragmentTransaction transaction = manager.beginTransaction(); 
    transaction.replace(R.id.linearLayoutLoginFragment, fragViewPolicy, "View Policy"); 
    transaction.commit(); 
} 

public void addMyProfile (View v){ 
    MyProfileFragment fragProfile = new MyProfileFragment(); 
    FragmentTransaction transaction = manager.beginTransaction(); 
    transaction.replace(R.id.linearLayoutLoginFragment, fragProfile, "My profile"); 
    transaction.commit(); 
} 

public void addMyPolicy (View v){ 
    MyPolicyFragment fragMyPolicy = new MyPolicyFragment(); 
    FragmentTransaction transaction = manager.beginTransaction(); 
    transaction.replace(R.id.linearLayoutLoginFragment, fragMyPolicy, "My Policy"); 
    transaction.commit(); 
} 

public void addUploadFragment (View v){ 
    UploadPhotoFragment fragUpload = new UploadPhotoFragment(); 
    FragmentTransaction transaction = manager.beginTransaction(); 
    transaction.replace(R.id.linearLayoutLoginFragment, fragUpload, "Uploaded Policy"); 
    transaction.commit(); 
} 

public void addUploadedFragment (View v){ 
    UploadedPolicyFragment fragUploaded = new UploadedPolicyFragment(); 
    FragmentTransaction transaction = manager.beginTransaction(); 
    transaction.replace(R.id.linearLayoutLoginFragment, fragUploaded, "Uploaded Policy"); 
    transaction.commit(); 
} 



@Override 
public void policyName(String name) { 
    Log.d("Luffy","Inside PolicyName AfterLogin"); 
    ListPolicies fragList = new ListPolicies(); 
    FragmentTransaction transaction = manager.beginTransaction(); 
    fragList.polName(name); 
    transaction.replace(R.id.linearLayoutLoginFragment, fragList, "Uploaded Policy"); 
    transaction.commit(); 
} 
} 

輸出：

10-28 14:00:18.400 2174-2174/onepiece.luffy.investaccui D/Luffy: Inside PolicyName AfterLogin 
10-28 14:00:18.400 2174-2174/onepiece.luffy.investaccui D/Luffy: Posnull 
10-28 14:00:18.400 2174-2174/onepiece.luffy.investaccui D/Luffy: Pos0 

我想輸出：

10-28 14:00:18.400 2174-2174/onepiece.luffy.investaccui D/Luffy: Inside PolicyName AfterLogin 
10-28 14:00:18.400 2174-2174/onepiece.luffy.investaccui D/Luffy: Pos0 

，這樣我可以打電話給我Engineering_insurance的ListView

需要您的幫助傢伙... 在此先感謝

Answer 1

String polname = polName(polnames); 

用於創建polname字符串。

public String polName(String name){ 


if(name!=null) { 
    polnames = name; 


} 
Log.d("Luffy", "Pos" +polnames); 
    return polnames; 

}

是所描述的方法。如果name！= null polonaise = name。

從

String polname = polName(polnames); 

的說法是 「polonames」 的變量，它在這裏宣佈

String polnames; 

，但從來沒有初始化