切換運行時的錯誤StartActivity

Question

我最近在從我的啓動畫面加載登錄活動時發生錯誤。這導致了致命的崩潰。

下面是代碼：

if(response.contains("Success") && isStored == false){ 
    Intent Login = new Intent(SplashScreen.this, LoginScreen.class); 
    Login.putExtra("EXTRA_PHONE_NUMBER", phoneNumber); 
    startActivity(Login); 

    // close this activity 
    finish(); 
    } 

我注意到，如果我切換LoginScreen.class與我mainactivity.class，它工作正常。有沒有人知道這裏發生了什麼事？

下面是代碼到LoginScreen：

public class LoginScreen extends Activity { 
EditText email; 
EditText pass; 
Button LoginButton; 
ImageView image; 
String phoneNumber; 
String userPhone; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    //These 2 lines hide the action bar 
    getWindow().requestFeature(Window.FEATURE_ACTION_BAR); 
    getActionBar().hide(); 
    setContentView(R.layout.activity_login); 
    email = (EditText)findViewById(R.id.emailTxt); 
    pass = (EditText)findViewById(R.id.passwordTxt); 

    image = (ImageView)findViewById(R.id.ImageViewLogo); 
    userPhone = getPhoneNumber(); 

    //Displays the logo in the ImageViewLogo 
    image.setImageResource(R.drawable.autotrak_logo); 

    final String EMAIL_PATTERN = "^[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$"; 

    LoginButton.setOnClickListener(new View.OnClickListener() 
    { 
    @Override 
     public void onClick(View view) 
     { 
      final String userEmail = email.getText().toString(); 
      final String userPass = pass.getText().toString(); 

      if(userEmail.length() == 0) 
      { 
       email.requestFocus(); 
       email.setError("No Email Entered"); 
      } 
      else if(!userEmail.matches(EMAIL_PATTERN)) 
      { 
       email.requestFocus(); 
       email.setError("Invalid Email"); 
      } 
      else if(userPass.length() == 0) 
      { 
       pass.requestFocus(); 
       pass.setError("No Password Entered"); 
      }else if(checkForUser(userEmail, userPass).contains("Bad")){ 
       String toastText = "Incorrect email or password"; 
       Toast.makeText(getApplicationContext(), toastText, Toast.LENGTH_SHORT).show(); 
       pass.requestFocus(); 
      }else 
      { 
       SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getBaseContext()); 
       SharedPreferences.Editor editor = prefs.edit(); 
       editor.putString("storedEmail", userEmail); 
       editor.putString("storedPass", userPass); 
       editor.putString("storedPhone", userPhone); 
       editor.apply(); 

       Intent BluetoothDemo = new Intent(LoginScreen.this, BluetoothDemo.class); 
       startActivity(BluetoothDemo); 
      } 
     } 
    }); 
} 

public String checkForUser(String email, String pass) { 
    if (android.os.Build.VERSION.SDK_INT > 9) { 
     StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build(); 
     StrictMode.setThreadPolicy(policy); 
     try { 
      HttpClient client = new DefaultHttpClient(); 
      HttpPost request = new HttpPost("http://xxxx.xxxx.net/xxxx.php"); 
      ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(); 
      nameValuePairs.add(new BasicNameValuePair("email", email)); 
      nameValuePairs.add(new BasicNameValuePair("password", pass)); 
      nameValuePairs.add(new BasicNameValuePair("phoneNumber", userPhone)); 
      try { 
       request.setEntity(new UrlEncodedFormEntity(nameValuePairs)); 
       HttpResponse response = client.execute(request); 
       HttpEntity entity = response.getEntity(); 
       InputStream is = entity.getContent(); 
       BufferedInputStream bis = new BufferedInputStream(is); 
       ByteArrayBuffer baf = new ByteArrayBuffer(20); 

       int current = 0; 
       while((current = bis.read()) != -1) 
       { 
        baf.append((byte)current); 
       } 

       String bytesSent = new String(baf.toByteArray()); 

       // for receiving response from the server 
       return bytesSent; 
      } catch (Exception e) { 
       e.printStackTrace(); 
       String stackTrace = Log.getStackTraceString(e); 
       String toastText = "Error sending data: " + stackTrace; 
       Toast.makeText(getApplicationContext(), toastText, Toast.LENGTH_SHORT).show(); 
       return null; 
      } 
     } catch (Exception e) { 
      String toastText = "Error preparing data"; 
      Toast.makeText(getApplicationContext(), toastText, Toast.LENGTH_SHORT).show(); 
      return null; 
     } 
    } 
    return null; 
} 

public String getPhoneNumber(){ 
    Bundle extras; 
    extras = getIntent().getExtras(); 
    if(extras == null) { 
     phoneNumber = null; 
    } else { 
     phoneNumber = extras.getString("EXTRA_PHONE_NUMBER"); 
    } 
    return phoneNumber; 

} 

}

這裏是堆棧跟蹤：

11-23 13:08:00.626 1242-1242/my.obd2connector E/AndroidRuntime﹕ FATAL EXCEPTION: main 
Process: my.obd2connector, PID: 1242 
java.lang.RuntimeException: Unable to start activity ComponentInfo{my.obd2connector/my.obd2connector.LoginScreen}: java.lang.NullPointerException 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2305) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2363) 
     at android.app.ActivityThread.access$900(ActivityThread.java:161) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1265) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:157) 
     at android.app.ActivityThread.main(ActivityThread.java:5356) 
     at java.lang.reflect.Method.invokeNative(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:515) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081) 
     at dalvik.system.NativeStart.main(Native Method) 
Caused by: java.lang.NullPointerException 
     at my.obd2connector.LoginScreen.onCreate(LoginScreen.java:58) 
     at android.app.Activity.performCreate(Activity.java:5426) 
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2269) 
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2363) 
            at android.app.ActivityThread.access$900(ActivityThread.java:161) 
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1265) 
            at android.os.Handler.dispatchMessage(Handler.java:102) 
            at android.os.Looper.loop(Looper.java:157) 
            at android.app.ActivityThread.main(ActivityThread.java:5356) 
            at java.lang.reflect.Method.invokeNative(Native Method) 
            at java.lang.reflect.Method.invoke(Method.java:515) 
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265) 
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081) 
            at dalvik.system.NativeStart.main(Native Method) 

Answer 1

所致：顯示java.lang.NullPointerException

因爲在LoginScreen活動您呼叫LoginButton按鈕instance.so做的初始化前的LoginButtonsetOnClickListener方法setContentView後：

LoginButton = (Button)findViewById(R.id.Login_Button_ID);