片段通信，由於某種原因無法正常工作

我試圖通過將對象從一個片段傳遞到另一個片段來在兩個片段之間進行通信。在GradeListFragment中，我有一個listView，而在GradeInfoFragment中，顯示的細節取決於在listView上進行的選擇。我向日誌顯示消息，以確保可以訪問所需的方法並確保可以檢索碎片之間的信息，但我仍可以獲取NullPointerException，因爲某些原因，當我嘗試調用將處理碎片的方法時在我GradeInfoFragment數據片段通信，由於某種原因無法正常工作

GradeListActivity.java

package bcs421.jorgeramirez.hwk.gradeapp.presentation; 

import bcs421.jorgeramirez.hwk.gradeapp.businesslogic.GradeData; 
import android.app.Activity; 
import android.app.Fragment; 
import android.app.FragmentManager; 
import android.os.Bundle; 
import android.support.v4.app.FragmentActivity; 
import android.util.Log; 
import android.view.Surface; 
import android.app.FragmentTransaction; 


public class GradeListActivity extends FragmentActivity implements SendGrades { 

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


    FragmentManager fm = getFragmentManager(); 
    FragmentTransaction ft = fm.beginTransaction(); 
    ft.add(R.id.frag_container1, new GradeListFragment()); 


    int rotation = getWindowManager().getDefaultDisplay().getRotation(); 

    if((rotation == Surface.ROTATION_90) || (rotation == Surface.ROTATION_270)) 
    { 
     ft.add(R.id.frag_container2, new GradeInfoFragment()); 

    } 

    ft.commit(); 


} 

@Override 
public void sendGradeInfo(GradeData thisGrade) { 
    Log.d("Hello!", "In sendGradeInfo function!"); 
    Log.d("HEy!", "This category is: " + thisGrade.getCategory()); 
    GradeInfoFragment f2 = (GradeInfoFragment) getFragmentManager().findFragmentById(R.id.frag_container2); 
    f2.getData(thisGrade); 
} 






}

GradeListFragment.java

package bcs421.jorgeramirez.hwk.gradeapp.presentation; 

import java.io.Serializable; 
import java.util.ArrayList; 

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.app.Fragment; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.AdapterView; 
import android.widget.AdapterView.OnItemClickListener; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 
import bcs421.jorgeramirez.hwk.gradeapp.businesslogic.GradeCollection; 
import bcs421.jorgeramirez.hwk.gradeapp.businesslogic.GradeData; 


public class GradeListFragment extends Fragment implements Serializable, SendGrades { 



SendGrades SG; 
public GradeCollection collectedGrades; 

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

View v = inflater.inflate(R.layout.fragment_gradelist, container, false); 
ListView lv = (ListView) v.findViewById(R.id.listViewGrades); 

ArrayList<String> namesArrayList; 
ArrayAdapter<String> namesArrayAdapter; 


Activity a = getActivity(); 
Intent i = a.getIntent(); 

namesArrayList = i.getExtras().getStringArrayList("grade_list"); 
collectedGrades = (GradeCollection) i.getSerializableExtra("grade_collection"); 
namesArrayAdapter = new ArrayAdapter<String>(a, R.layout.item_gradelist, namesArrayList); 
lv.setAdapter(namesArrayAdapter); 
lv.setClickable(false); 
lv.setOnItemClickListener(new OnItemClickListener() { 
    @Override 
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 

      GradeData thisGrade = collectedGrades.GetItem(position); 
      Log.d("Hell!", "This category is: " + thisGrade.getCategory()); 
      SG.sendGradeInfo(thisGrade); 


    } 
    }); 


return v; 
} 




@Override 
public void onAttach (Activity activity) 
{ 
    super.onAttach(activity); 
    try 
    { 
     SG = (SendGrades)activity; 
    } 
    catch (ClassCastException e) 
    { 
     throw new ClassCastException("You need to implement the sendGradeInfo method"); 
    } 
} 




@Override 
public void sendGradeInfo(GradeData thisGrade) { 

    GradeInfoFragment f2 = (GradeInfoFragment)getFragmentManager().findFragmentById(R.id.frag_container2); 
    f2.getData(thisGrade); 
} 
}

GradeInfoFragment.java

package bcs421.jorgeramirez.hwk.gradeapp.presentation; 

import java.util.ArrayList; 

import bcs421.jorgeramirez.hwk.gradeapp.businesslogic.GradeData; 
import android.app.Activity; 
import android.app.Fragment; 
import android.content.Intent; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ArrayAdapter; 
import android.widget.EditText; 
import android.widget.ListView; 

public class GradeInfoFragment extends Fragment { 

EditText categoryText, numberText, gradeText, descText; 

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

View v = inflater.inflate(R.layout.fragment_gradeinfo, container, false); 


categoryText = (EditText)v.findViewById(R.id.editCat); 
numberText = (EditText)v.findViewById(R.id.editNumber); 
gradeText = (EditText)v.findViewById(R.id.editGrade); 
descText = (EditText)v.findViewById(R.id.editDesc); 

return v; 
} 

public void getData(GradeData receivedGrade) 
{ 
    double gd = receivedGrade.getGrade(); 
    String gValue = Double.toString(gd); 
    Log.d("Hello!", "Filling in grade information!"); 
    categoryText.setText(receivedGrade.getCategory()); 
    numberText.setText(receivedGrade.getNumber()); 
    gradeText.setText(gValue); 
    descText.setText(receivedGrade.getDescription()); 
} 

}

logcat的

04-06 13:26:28.161: D/Hell!(2229): This category is: Lab 
04-06 13:26:28.161: D/Hello!(2229): In sendGradeInfo function! 
04-06 13:26:28.161: D/HEy!(2229): This category is: Lab 
04-06 13:26:28.161: D/AndroidRuntime(2229): Shutting down VM 
04-06 13:26:28.161: W/dalvikvm(2229): threadid=1: thread exiting with uncaught exception (group=0xb1d44b20) 
04-06 13:26:28.161: E/AndroidRuntime(2229): FATAL EXCEPTION: main 
04-06 13:26:28.161: E/AndroidRuntime(2229): Process: bcs421.jorgeramirez.hwk.gradeapp.presentation, PID: 2229 
04-06 13:26:28.161: E/AndroidRuntime(2229): java.lang.NullPointerException 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at bcs421.jorgeramirez.hwk.gradeapp.presentation.GradeListActivity.sendGradeInfo(GradeListActivity.java:45) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at bcs421.jorgeramirez.hwk.gradeapp.presentation.GradeListFragment$1.onItemClick(GradeListFragment.java:55) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at android.widget.AdapterView.performItemClick(AdapterView.java:299) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at android.widget.AbsListView.performItemClick(AbsListView.java:1113) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at android.widget.AbsListView$PerformClick.run(AbsListView.java:2904) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at android.widget.AbsListView$3.run(AbsListView.java:3638) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at android.os.Handler.handleCallback(Handler.java:733) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at android.os.Handler.dispatchMessage(Handler.java:95) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at android.os.Looper.loop(Looper.java:136) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at android.app.ActivityThread.main(ActivityThread.java:5017) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at java.lang.reflect.Method.invokeNative(Native Method) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at java.lang.reflect.Method.invoke(Method.java:515) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
04-06 13:26:28.161: E/AndroidRuntime(2229):  at dalvik.system.NativeStart.main(Native Method)

來源

2015-04-06 Jorge Ramirez

請您在sendGradeInfo方法F2實例......這不應該是空 –

嘗試調試你的應用程序。 f2是空參數嗎？ – natario

嘿傢伙！我運行了一條if語句，如果f2爲null，並且f2確實爲null，則會向Logcat發送消息。我不知道爲什麼！ –

嘗試將所有碎片爲支持android.support.v4.app.Fragment
，而是getFragmentManager()使用getSupportFragmentManager()

來源

2015-04-06 18:13:34 user2650128

我也試過這個，但f2仍然是空的！ –

試試這個，在這一行，

GradeInfoFragment f2 = (GradeInfoFragment)getFragmentManager().findFragmentById(R.id.frag_container2);

您試圖使用「R.id.frag_container2」獲取片段，但這不是片段的id /標記。它的容器ID。所以它返回null。

爲了通過標記獲取片段，您必須在添加標記時將標記設置爲片段。

嘗試，

ft.add(R.id.frag_container2, new GradeInfoFragment(), "your_tag_name");

來源

2015-04-06 18:20:36

我試過這個和f2仍然是空的:( –

發表您的整個代碼plz –

片段通信，由於某種原因無法正常工作

回答

相關問題