碎片碎片通信，由于某种原因无法正常工作

时间：2015-04-06 17:57:43

标签： android object nullpointerexception fragment communication

我试图通过将一个对象从一个片段传递到另一个片段来在两个片段之间进行通信。在GradeListFragment中，我有一个listView，在GradeInfoFragment中，根据listView上的选择显示详细信息。我向日志显示消息以确保我可以到达所需的方法并确保我可以检索片段之间的信息，我可以这样做但是当我尝试调用将处理该方法的方法时，由于某种原因我仍然会得到NullPointerException我的GradeInfoFragment中的数据

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)

2 个答案:

答案 0 :(得分：0)

尝试将所有片段设置为支持android.support.v4.app.Fragment
而getFragmentManager()使用getSupportFragmentManager()

答案 1 :(得分：0)

试试这个， 在这一行中，

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

您正在尝试使用“R.id.frag_container2”获取片段，但这不是片段的ID /标记。它的容器ID。所以它返回null。

为了按标记获取片段，您必须在添加标记时将标记设置为片段。

尝试，

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