Android 从FragmentActivity调用活动时出现NullPointerException

我有一个活动扩展了FragmentActivity，比如MainActivity，它包含两个片段，比如F1，F2。在F1 fragment中，调用AsyncTask并在MainActivity中实现接口，即FragmentActivity。在该接口方法中，尝试调用新活动，比如说使用下面的代码扩展活动的SecondActivity，但它抛出异常

Intent intent = new Intent(MainActivity.this, SecondActivity.class);
startActivity(intent);

请帮忙

代码 MainActivity.java

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.widget.TextView;

// Import

public class MainActivity extends FragmentActivity implements 
SavePaymentInterface, GetDiscountInterface{

    private final String TAG = "MainActivity";
    public static Context mContext;
    public static AppData mAppData;
    public static WebServiceFunctions Obj_WebServiceFunctions;
    public static Common obj_Common;

    //var init

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);        

        init();
        initView();
    }

    @SuppressLint("NewApi")
    private void init() throws NotFoundException {

        actionBar = getActionBar();
        actionBar.setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);
        actionBar.setCustomView(R.layout.actionbar_view);
        actionBar.setBackgroundDrawable(getResources().getDrawable(
                R.drawable.top_portrait));

        mAppSectionsPagerAdapter = new AppSectionsPagerAdapter(getSupportFragmentManager());

        mViewPager = (CustomViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mAppSectionsPagerAdapter);

        mContext = this;

        mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {

                mTabHost.setCurrentTab(position);

            }
        });

    }

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

        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // TODO Auto-generated method stub
        switch (item.getItemId()) {
        case R.id.action_logout:

            break;

        case R.id.action_print:

            showAlertDialog(mContext.getString(R.string.STR_TITLE_RECEIPT_PRINT),
                    mContext.getString(R.string.STR_MESSAGE_RECEIPT_PRINT));

            break;

        case R.id.action_more:

            break;

        default:
            return super.onOptionsItemSelected(item);
        }
        return true;
    }

    private void initView() {

        try {

            setupTabHost();

            setupTab(new TextView(this), getString(R.string.TAB_TICKET),
                    0);
            setupTab(new TextView(this), getString(R.string.TAB_CASHIER), 1);


        } catch (Exception e) {

            LogFile.writeLOG(TAG, "@initView(): " + e.toString());
        }

        addTabListener();

    }


    public static class AppSectionsPagerAdapter extends FragmentPagerAdapter {

        public AppSectionsPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int i) {
            switch (i) {
            case 0:
                MainActivity m = new MainActivity();
                return m.new TicketFragment();

            default:

                MainActivity m1 = new MainActivity();
                return m1.new CashierFragment();

            }
        }

        @Override
        public int getCount() {
            return 2;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return "Section " + (position + 1);
        }
    }

    /**
     * A fragment that launches other parts of the demo application.
     */
    @SuppressLint("ValidFragment")
    public class TicketFragment extends Fragment {

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.lay_ticket, container, false);

            //variable init

            return rootView;
        }

        @Override
        public void onPause() {
            super.onPause();

        }

        @Override
        public void onResume() 
        {

            super.onResume();


        }

    }


    @SuppressLint("ValidFragment")
    public class CashierFragment extends Fragment {

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

            View rootView = inflater.inflate(R.layout.lay_cashier, container, false);

            //variable init          

            rootView.findViewById(R.id.btnSearch)
            .setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {

                    // some code
                }
            });

            rootView.findViewById(R.id.btnValidations)
            .setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) { 

                    try {
                        new AsyncGetDiscountList(mContext, MainActivity.this,
                                Obj_WebServiceFunctions).execute();


                    } catch (Exception e) {

                        LogFile.writeLOG(TAG,
                                ": " + e.toString());

                    }
                }
            });

            rootView.findViewById(R.id.btnPayment)
            .setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View view) { 

                    try {

                        new AsyncSavePayment(mContext,
                                MainActivity.this,
                                Obj_WebServiceFunctions).execute();

                    } catch (Exception e) {

                        LogFile.writeLOG(TAG, ": "
                                + e.toString());
                    }


                }

            });

            return rootView;
        }

        @Override
        public void onPause() {
            super.onPause();

        }

        @Override
        public void onResume() {

            super.onResume();

        }

    }

    public void showAlertDialog(String strTitle, String strMessage) {

        try {

            // some code
            txtTitle.setText(strTitle);
            txtMessage.setText(strMessage);

            Button ok = (Button) mDialog.findViewById(R.id.btnYes);

            ok.setOnClickListener(new OnClickListener() {
                public void onClick(View v) {

                    receiptPrint();
                }
            });


            Button cancel = (Button) mDialog.findViewById(R.id.btnNo);

            cancel.setText(mContext.getString(R.string.STR_LBL_NO));
            cancel.setOnClickListener(new OnClickListener() {
                public void onClick(View v) {

                    mDialog.dismiss();

                }
            });

            mDialog.show();

        } catch (Exception e) {

            LogFile.writeLOG(TAG, "@showAlertDialog(): " + e.toString());
        }
    }

    private void receiptPrint() {

        try {

            Intent intent = new Intent(MainActivity.this, PrintReceiptActivity.class);
            intent.putExtra("print", isPrint); // throws nullpointer exception
            startActivity(intent);

        } catch (Exception e) {

            LogFile.writeLOG(TAG, "@receiptPrint(): " + e.toString());
        }

    }

    @Override
    public void onPaymentDone(String response) {

        try {

            if (response) { //condition for response validility

                isPrint = true;
                showAlertDialog(
                        mContext.getString(R.string.STR_TITLE_RECEIPT_PRINT),
                        mContext.getString(R.string.STR_MESSAGE_RECEIPT_PRINT));

            } 

        } catch (Exception e) {

            LogFile.writeLOG(TAG, "@onPaymentDone(): " + e.toString());
        }

    }


    @Override
    public Common getCommon() {
        return obj_Common;
    }


    private void addTabListener() {

        mTabHost.setOnTabChangedListener(new OnTabChangeListener() {

            @Override
            public void onTabChanged(String tabId) {

                try {
                    if (mTabHost.getCurrentTab() == 0) {

                        // some code

                    } else if (mTabHost.getCurrentTab() == 1) {

                        // some code
                    }

                } catch (Exception e) {
                    e.printStackTrace();
                    LogFile.writeLOG(TAG, "@addTabListener(): " + e.toString());
                }

            }
        });

    }

    private void setupTabHost() {
        mTabHost = (TabHost) findViewById(android.R.id.tabhost);
        mTabHost.setup();
    }

    private void setupTab(final View view, final String tag, int index) {

        try {

            View tabview = createTabView(mTabHost.getContext(), tag, index);

            TabSpec setContent = mTabHost.newTabSpec(tag).setIndicator(tabview).setContent(new TabContentFactory() {

                @Override
                public View createTabContent(String tag) {

                    return view;
                }
            });

            mTabHost.addTab(setContent);

        } catch (Exception e) {
            LogFile.writeLOG(TAG, "@setupTab(): " + e.toString());
        }

    }

    private View createTabView(final Context context, final String text,
            int index) {

        try {

            View view = LayoutInflater.from(getApplicationContext()).inflate(
                    R.layout.lay_tabs_bg, null);
            TextView tv = (TextView) view.findViewById(R.id.tabsText);
            tv.setText(text);

            if (index == 0) {
                tv.setCompoundDrawablesWithIntrinsicBounds(R.drawable.ticket_icon, 0, 0, 0);
            } else {
                tv.setCompoundDrawablesWithIntrinsicBounds(R.drawable.cashier_icon, 0, 0, 0);
            }

            return view;

        } catch (Exception e) {

            LogFile.writeLOG(TAG, "@createTabView(): " + e.toString());
            return null;
        }
    }

    @Override
    public void onBackPressed() {

    }


    @Override
    public void onDestroy() {
        super.onDestroy();

    }

    @Override
    public void onPause() {
        super.onPause();

    }

    @Override
    public void onResume() {

    }

    @Override
    public void onStart() {
        super.onStart();

    }

    @Override
    protected void onRestart() {
        super.onRestart();

    }

    @Override
    public void onGetDiscount(String response) {

        try {

            Intent intent = new Intent(MainActivity.this, SecondActivity.class); // throws nullpointer exception
            startActivity(intent);

        } catch (Exception e) {

        }

    }
}

日志：

09-30 17:52:21.143: E/AndroidRuntime(10600): FATAL EXCEPTION: main
09-30 17:52:21.143: E/AndroidRuntime(10600): java.lang.NullPointerException
09-30 17:52:21.143: E/AndroidRuntime(10600):    at android.content.ContextWrapper.getPackageName(ContextWrapper.java:135)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at android.content.ComponentName.<init>(ComponentName.java:75)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at android.content.Intent.<init>(Intent.java:3678)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at com.vale.activity.MainActivity.receiptPrint(MainActivity.java:1093)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at com.vale.activity.activity.MainActivity.access$4(MainActivity.java:1075)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at com.vale.activity.activity.MainActivity$11.onClick(MainActivity.java:1048)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at android.view.View.performClick(View.java:4243)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at android.view.View$PerformClick.run(View.java:17731)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at android.os.Handler.handleCallback(Handler.java:730)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at android.os.Handler.dispatchMessage(Handler.java:92)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at android.os.Looper.loop(Looper.java:137)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at android.app.ActivityThread.main(ActivityThread.java:5136)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at java.lang.reflect.Method.invokeNative(Native Method)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at java.lang.reflect.Method.invoke(Method.java:525)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-30 17:52:21.143: E/AndroidRuntime(10600):    at dalvik.system.NativeStart.main(Native Method)

09-3017:52:21.143:E/AndroidRuntime（10600）：致命异常：main
09-30 17:52:21.143:E/AndroidRuntime（10600）：java.lang.NullPointerException
09-30 17:52:21.143:E/AndroidRuntime（10600）：位于android.content.ContextWrapper.getPackageName（ContextWrapper.java:135）
09-30 17:52:21.143:E/AndroidRuntime（10600）：在android.content.ComponentName.（ComponentName.java:75）
09-30 17:52:21.143:E/AndroidRuntime（10600）：在android.content.Intent.（Intent.java:3678）
09-30 17:52:21.143:E/AndroidRuntime（10600）：位于com.vale.activity.MainActivity.receiptPrint（MainActivity.java:1093）
09-30 17:52:21.143:E/AndroidRuntime（10600）：位于com.vale.activity.activity.MainActivity.access$4（MainActivity.java:1075）
09-30 17:52:21.143:E/AndroidRuntime（10600）：位于com.vale.activity.activity.MainActivity$11.onClick（MainActivity.java:1048）
09-30 17:52:21.143:E/AndroidRuntime（10600）：在android.view.view.performClick（view.java:4243）
09-30 17:52:21.143:E/AndroidRuntime（10600）：在android.view.view$PerformClick.run（view.java:17731）
09-30 17:52:21.143:E/AndroidRuntime（10600）：在android.os.Handler.handleCallback（Handler.java:730）上
09-30 17:52:21.143:E/AndroidRuntime（10600）：在android.os.Handler.dispatchMessage（Handler.java:92）上
09-30 17:52:21.143:E/AndroidRuntime（10600）：在android.os.Looper.loop（Looper.java:137）
09-30 17:52:21.143:E/AndroidRuntime（10600）：位于android.app.ActivityThread.main（ActivityThread.java:5136）
09-30 17:52:21.143:E/AndroidRuntime（10600）：位于java.lang.reflect.Method.Invokenactive（本机方法）
09-30 17:52:21.143:E/AndroidRuntime（10600）：位于java.lang.reflect.Method.invoke（Method.java:525）
09-30 17:52:21.143:E/AndroidRuntime（10600）：在com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run（ZygoteInit.java:737）
09-30 17:52:21.143:E/AndroidRuntime（10600）：位于com.android.internal.os.ZygoteInit.main（ZygoteInit.java:553）
09-30 17:52:21.143:E/AndroidRuntime（10600）：在dalvik.system.NativeStart.main（本机方法）

什么也没做就解决了问题。一整天我都在绞尽脑汁寻找上述问题的原因。第二天，我编译了代码，它成功地运行了，没有任何异常。奇怪……）

您还可以共享日志详细信息吗？发布日志详细信息。您可以发布

AndroidManifest.xml

？@PageNotFound在清单文件中提到了该活动。。我检查了..

SecondACtivity

，拼写错误？应该是

SecondActivity

。