NullPointerException引起：task.execute（“”）;

Question

我执行我的应用程序时收到空指针异常，我不知道为什么。该问题发生在线上：

task.execute(""); 

但我不知道为什么这会返回空指针异常。 （我已经验证我有互联网连接和它连接到XML文件是完整和功能。）

来源：

public class UpdateActivity extends Activity implements OnClickListener { 

    public static int TotalSteps = 8; 
    private TelephonyManager tm; 

    private Button mUpdateButton = null; 
    private Button mAssistUpdateButton = null; 
    private Button mAssistInstrButton = null; 
    private TextView mReadAgainButton = null; 
    private int mInstructionNumber = 0; 
    AlertDialog mConfirmAlert = null; 
    private NetworkTask task; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     tm = (TelephonyManager) getSystemService(TELEPHONY_SERVICE); 
     int networkType = tm.getNetworkType(); 
     int phoneType = tm.getPhoneType(); 
     int version = android.os.Build.VERSION.SDK_INT; 
     if (phoneType == TelephonyManager.PHONE_TYPE_CDMA 
       || (phoneType != TelephonyManager.PHONE_TYPE_GSM 
       && networkType != TelephonyManager.NETWORK_TYPE_GPRS 
       && networkType != TelephonyManager.NETWORK_TYPE_EDGE 
       && networkType != TelephonyManager.NETWORK_TYPE_HSDPA 
       && networkType != TelephonyManager.NETWORK_TYPE_HSPA 
       && networkType != TelephonyManager.NETWORK_TYPE_HSPAP 
       && networkType != TelephonyManager.NETWORK_TYPE_HSUPA 
       && networkType != TelephonyManager.NETWORK_TYPE_UMTS && networkType != TelephonyManager.NETWORK_TYPE_LTE)) { 
      // If the phone type is CDMA or 
      // the phone phone type is not GSM and the network type is none of 
      // the network types indicated in the statement 
      // Display incompatibility message 
      showAlert(getString(R.string.incomp_sm_dialog)); 
      // Network type is looked because some tablets have no phone type. 
      // We rely on network type in such cases 
     } else if (!(tm.getSimState() == TelephonyManager.SIM_STATE_ABSENT 
       || (tm.getSimOperator()) 
       .equals(getString(R.string.numeric_tmo)) || (tm 
         .getSimOperator()).equals(getString(R.string.numeric_att)))) { 
      // if SIM is present and is NOT a T-Mo network SIM, 
      // display Error message alert indicating to use SM SIM 
      showAlert(getString(R.string.insert_sm_dialog)); 
     }// No SIM or SIM with T-Mo MNC MCC present 
     else if (version < VERSION_CODES.ICE_CREAM_SANDWICH) { 
      // Initial UI setup for versions lower than ICS 
      setContentView(R.layout.update); 
      mUpdateButton = (Button) findViewById(R.id.update_button); 

      mUpdateButton.setOnClickListener(this); 
     } else {// ICS and up 

      // task.execute(); 

      if ((tm.getSimOperator()).equals(getString(R.string.numeric_tmo)) 
        || (tm.getSimOperator()) 
        .equals(getString(R.string.numeric_att))) { 
       task.execute(""); 
       // Device has T-Mo network SIM card MCC and MNC correctly 
       // populated 
       // Reduce number of steps to 6 
       TotalSteps = 6; 
      } 
      // 
      // Initial UI setup for ICS and up 

      setContentView(R.layout.assist_update); 
      String assistUpdate = getString(R.string.apn_app_text_cta2); 
      CharSequence styledText = Html.fromHtml(assistUpdate); 
      TextView assistText = (TextView) findViewById(R.id.apn_app_text_cta2); 
      assistText.setText(styledText); 
      mAssistUpdateButton = (Button) findViewById(R.id.assist_update_btn); 
      mAssistUpdateButton.setOnClickListener(this); 
     } 
    } 

    public void onClick(View v) { 

     if (v == mUpdateButton) { 
      // Update button for versions lower than ICS is selected 
      // setContentView(R.layout.updating); 
      onClickMethod(v); 

      Intent i = new Intent(this, ConfigFinalActivity.class); 
      startActivity(i); 
      finish(); 
     } else if (v == mAssistUpdateButton) { 

      // Update button for ICS and up is selected 
      // Get the TextView in the Assist Update UI 
      TextView tv = (TextView) findViewById(R.id.apn_app_text_cta2); 
      String text = ""; 
      CharSequence styledText = text; 
      switch (mInstructionNumber) { 
      case 0: 
       // Retrieve the instruction string resource corresponding the 
       // 2nd set of instructions 
       text = String.format(getString(R.string.apn_app_text_instr), 
         TotalSteps); 
       styledText = Html.fromHtml(text); 
       // Update the TextView with the correct set of instructions 
       tv.setText(styledText); 
       // Increment instruction number so the correct instructions 
       // string resource can be retrieve the next time the update 
       // button is pressed 
       mInstructionNumber++; 
       break; 
      case 1: 
       text = getString(R.string.apn_app_text_instr2); 
       styledText = Html.fromHtml(text); 
       tv.setText(styledText); 
       // Increment instruction number so the correct instructions 
       // string resource can be retrieve the next time the update 
       // button is pressed 
       mInstructionNumber++; 
       break; 
      case 2: 
       // Final set of instructions-Change to the corresponding layout 

       setContentView(R.layout.assist_instructions); 
       String assistUpdateInstr = String.format(
         getString(R.string.apn_app_text_instr3), TotalSteps); 
       styledText = Html.fromHtml(assistUpdateInstr); 
       TextView assistInstrText = (TextView) findViewById(R.id.updated_text); 
       assistInstrText.setText(styledText); 
       mAssistInstrButton = (Button) findViewById(R.id.assist_instr_btn); 
       mReadAgainButton = (TextView) findViewById(R.id.read_again_btn); 
       mAssistInstrButton.setOnClickListener(this); 
       mReadAgainButton.setOnClickListener(this); 
      } 
     } else if (v == mAssistInstrButton) { 
      // "LET'S DO THIS" Button in final instructions screen for ICS and 
      // up is selected 
      // Create ConfigActivity Intent 
      Intent i = new Intent(this, ConfigFinalActivity.class); 
      // Invoke ConfigActivity Intent to start the assisted update 
      startActivity(i); 
      finish(); 
     } else if (v == mReadAgainButton) { 
      // go back to 1st set of instructions if read again is selected 
      mInstructionNumber = 0; 
      setContentView(R.layout.assist_update); 
      String assistUpdate = getString(R.string.apn_app_text_cta2); 
      CharSequence styledText = Html.fromHtml(assistUpdate); 
      TextView assistText = (TextView) findViewById(R.id.apn_app_text_cta2); 
      assistText.setText(styledText); 
      mAssistUpdateButton = (Button) findViewById(R.id.assist_update_btn); 
      mAssistUpdateButton.setOnClickListener(this); 
     } 
    } 

    public void onClickMethod(View v) { 
     mUpdateButton = (Button) findViewById(R.drawable.btn_update_active_hdpi); 

    } 

    private void showAlert(String message) { 
     AlertDialog.Builder builder = new AlertDialog.Builder(this); 
     builder.setMessage(message).setPositiveButton("OK", 
       new DialogInterface.OnClickListener() { 
      public void onClick(DialogInterface dialog, int id) { 
       UpdateActivity.this.finish(); 
      } 
     }); 
     mConfirmAlert = builder.create(); 
     mConfirmAlert.show(); 
    } 

} 

Answer 1

据我所知，你永远不会初始化task。你在这里声明

private NetworkTask task; 

但你需要在调用​​之前初始化。像

task = new NetworkTask(); // pass params to constructor if needed 
task.execute();