调用自定义活动子类时出现NullPointerException

时间：2011-04-21 18:19:33

标签： java android

我有一个通用基本活动，在onStart()方法中有一些身份验证代码需要在每个Activity中执行。但是，如果我在我的一个真实活动中将其子类化，并尝试启动其中一个，我会得到一个NPE。

这是我正在使用的一些代码

登录屏幕

public class Login extends Activity {

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

    private void configureEventHandlers()
    {
        mLoginBtn.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                mLoginModel.setPassword(mPwdTxt.getText().toString());
                mLoginModel.setUserName(mLoginTxt.getText().toString());

                // Call the network

                List<NameValuePair> paramTable = new ArrayList<NameValuePair>(2);
                paramTable.add(new BasicNameValuePair("email", mLoginModel.getUserName()));
                paramTable.add(new BasicNameValuePair("password", mLoginModel.getPassword()));
                mSpinner = ProgressDialog.show(Login.this, "Working", "Logging in ..");
                login(paramTable);              
            }
        });
        mClearBtn.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                mLoginTxt.setText("");
                mPwdTxt.setText("");
            }
        });

    }
    private void login(List<NameValuePair> paramTable) {
        NetworkParams params = new NetworkParams();
        params.setMethodName("ValidateLogin");
        params.setUrl(UserContext.GLOBAL_IP);
        params.setParams(paramTable);
        ResponseHandler handler = new ResponseHandler() {
            @Override
            public void requestSucceded(NetworkResult result) {
                parseResponseFromNetwork(result.getResponseMessage());
            }

            @Override
            public void requestFailed(NetworkResult result) {
                new AlertDialog.Builder(Login.this).setTitle("Attention").setMessage("Could not contact PPK's servers. " +
                        "This could be because of low signal strength. Please try later or contact support if " +
                        "the problem persists")
                .setNeutralButton("Close", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dlg, int sumthin) { // do nothing Ð it will close on its own
                    } 
                }
                ).show();
                mSpinner.dismiss();
            }
        };
        params.setHandler(handler);
        NetworkAccessClass nac = new NetworkAccessClass();
        nac.execute(params);
    }

    private void parseResponseFromNetwork(String responseMessage) {

        try {
            LoginXmlParser parser = new LoginXmlParser(mLoginModel);

            AsyncXmlParserParams params = new AsyncXmlParserParams();
            params.setHandler(parser);
            params.setListener(new AsyncXmlListener() {
                @Override
                public void asyncXmlParsingCompleted(Object parsedObject) {
                    // Dismiss the "waiting" progress indicator _after_ the parsing 
                    // the login xml. Avoids the delay between the pop up going away and Facility screen coming up.
                    mSpinner.dismiss();
                    mLoginModel = (LoginDataModel) parsedObject;
                    if(parsedObject == null || mLoginModel.getValid() == null) { 
                        authFailed(); 
                        return; 
                    }
                    if(((LoginDataModel) parsedObject).getValid()) {
                        // Works fine till here. The LoginDataModel object that I have looks okay
                        authSucceeded();
                    }
                    else
                    {
                        authFailed();
                    }
                }
            });
            params.setRequestString(responseMessage);

            AsyncXmlParser asyncParser = new AsyncXmlParser();
            asyncParser.execute(params);
        }
        catch(Exception e) {
            authFailed();
            Log.i("PPKMobileChargeCaptureException",e.getMessage());
        }
        return;
    }
    private void authSucceeded() {
        // Handle pushing facility screen
        try {
            Intent facilityLaunchIntent = new Intent(Login.this, FacilityScreen.class);
            Login.this.startActivity(facilityLaunchIntent);
        }
        catch(Exception ex)
        {
            String stackTrace = ex.getStackTrace().toString();
        }
    }
}

设施屏幕

public class FacilityScreen extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.facilityscreen);
        configureListView();
        configureEventHandlers();
        configureContext();
    }
    @Override
    protected void onStart()
    {
        super.onStart();
        if(mFacilityModel == null || mFacilityModel.size() == 0 || mUserPrefModel == null || mUserPrefModel.isEmpty()) {
            displayProgressIndicator();
            getPreferences();
            getFacilityList();
        }
    }
    @Override
    protected void onDestroy()
    {
        UserContext.clearUserPrefs();
        super.onDestroy();
    }
}

设施屏幕 - 修改

public class FacilityScreen extends PPKBaseActivity
{
    // onCreate, onResume etc. **This doesn't work, NPE**
}

PPKBaseActivity 

public class PPKBaseActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
    }

    @Override
    protected void onStart()
    {
        if(!UserContext.isUserLoggedIn()) {
            this.finish();
        }
        super.onStart();
    }

    @Override
    protected void onResume()
    {
        super.onResume();
    }

    @Override
    protected void onPause()
    {
        super.onPause();
    }

    @Override
    protected void onStop()
    {
        super.onStop();
    }

    @Override
    protected void onDestroy()
    {
        super.onDestroy();
    }

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

}

我错过了一些非常简单的事情吗？

谢谢，
的Teja。

编辑：添加了更多代码。还要提一下，FacilityScreen的{​​{1}}方法中的断点根本没有被击中。

EDIT2：堆栈跟踪。 （不太熟悉Android + Eclipse，这需要什么？）

onCreate()

的AndroidManifest.xml 

ex  InvocationTargetException  (id=830084855920)    
    cause   RuntimeException  (id=830085267584) 
        cause   NullPointerException  (id=830085217952) 
        detailMessage   "Unable to instantiate activity ComponentInfo{com.PatientPoint.MCC/com.PatientPoint.MCC.FacilityScreen}: java.lang.NullPointerException" (id=830084938528)  
        stackState   (id=830084989144)  
        stackTrace  null    
    detailMessage   null    
    stackState   (id=830084855952)  
    stackTrace  null    
    target  RuntimeException  (id=830085267584) 


Thread [<3> main] (Suspended (exception RuntimeException))  
    ActivityThread.performLaunchActivity(ActivityThread$ActivityRecord, Intent) line: 2417  
    ActivityThread.handleLaunchActivity(ActivityThread$ActivityRecord, Intent) line: 2512   
    ActivityThread.access$2200(ActivityThread, ActivityThread$ActivityRecord, Intent) line: 119 
    ActivityThread$H.handleMessage(Message) line: 1863  
    ActivityThread$H(Handler).dispatchMessage(Message) line: 99 
    Looper.loop() line: 123 
    ActivityThread.main(String[]) line: 4363    
    Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]  
    Method.invoke(Object, Object...) line: 521  
    ZygoteInit$MethodAndArgsCaller.run() line: 860  
    ZygoteInit.main(String[]) line: 618 
    NativeStart.main(String[]) line: not available [native method]

编辑3（最终）：

非常感谢你的帮助！我的道歉，因为我已经发现我没有包含在源代码中的一行代码导致异常。带有行号的<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.PatientPoint.MCC" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".Login" android:label="@string/app_name" android:theme="@android:style/Theme.NoTitleBar"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name=".FacilityScreen" android:label="" android:theme="@android:style/Theme.NoTitleBar"> <intent-filter> <action android:name="CATEGORY_ALTERNATIVE"></action> </intent-filter> </activity> <uses-sdk android:minSdkVersion="4" /> <uses-permission android:name="android.permission.INTERNET" /> </manifest> 输出帮助我缩小了范围。我的ex.printStackTrace()课程中也有一个SharedPreferenceManager负责这一切。再次道歉，谢谢你的时间！

2 个答案:

答案 0 :(得分：0)

感谢您快速回复（也感谢您的耐心等待）。

您应该从

中删除.（点） 
<activity android:name=".FacilityScreen"

行，所以它看起来像

<activity android:name="FacilityScreen"

此外，如果您还想使用其他活动，则应在androidManifes.xml文件中列出所有活动。

答案 1 :(得分：0)

04-21 19:25:11.646: ERROR/AndroidRuntime(339): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.PatientPoint.MCC/com.PatientPoint.MCC.FacilityScreen}: java.lang.NullPointerException
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2417)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at android.app.ActivityThread.access$2200(ActivityThread.java:119)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at android.os.Looper.loop(Looper.java:123)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at android.app.ActivityThread.main(ActivityThread.java:4363)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at java.lang.reflect.Method.invokeNative(Native Method)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at java.lang.reflect.Method.invoke(Method.java:521)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at dalvik.system.NativeStart.main(Native Method)
04-21 19:25:11.646: ERROR/AndroidRuntime(339): Caused by: java.lang.NullPointerException
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:146)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at com.PatientPoint.MCC.PPKBaseActivity.<init>(PPKBaseActivity.java:20)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at com.PatientPoint.MCC.FacilityScreen.<init>(FacilityScreen.java:54)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at java.lang.Class.newInstanceImpl(Native Method)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at java.lang.Class.newInstance(Class.java:1479)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2409)
04-21 19:25:11.646: ERROR/AndroidRuntime(339):     ... 11 more

我的PPKBaseActivity类中有一行代码如下：

SharedPreferences currentUserPrefs = getSharedPreferences(SHARED_PREFS_NAME, Context.MODE_PRIVATE);

由于某种原因导致NullPointerException。我现在没有使用它，所以我删除了那行代码，它似乎有效。

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