Java.lang.RuntimeException: Cannot start ComponentInfo activity

Question

I know that this error has appeared on the forum millions of times, but please help me find what I missed. I'm trying to make a simple tab-oriented application, I have few (except for errors)

1) my main activity is based on the tablayout tutorial that I found

public class MainTabPanel extends TabActivity { public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.mainlayout); Resources res = getResources(); TabHost tabHost = getTabHost(); TabHost.TabSpec spec; Intent intent; intent = new Intent().setClass(this, MyBookActivity.class); spec = tabHost.newTabSpec("main") .setIndicator("Main", res.getDrawable(R.drawable.ic_mybook)) .setContent(intent); tabHost.addTab(spec); tabHost.setCurrentTab(0); } } 

2) mainlayout.xml

 <?xml version="1.0" encoding="utf-8"?> <TabHost xmlns:android="http://schemas.android.com/apk/res/android" android:id="@android:id/tabhost" android:layout_width="fill_parent" android:layout_height="fill_parent"> <LinearLayout android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" android:padding="5dp"> <TabWidget android:id="@android:id/tabs" android:layout_width="fill_parent" android:layout_height="wrap_content" /> <FrameLayout android:id="@android:id/tabcontent" android:layout_width="fill_parent" android:layout_height="fill_parent" android:padding="5dp" /> </LinearLayout></TabHost> 

3) my second activity is basically almost empty, it just displays the current date and time, worked before I tried to add a tab bar

4) my manifest file

 <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.th.mybook" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="8" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:name=".MainTabPanel" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name="MyBookActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.ALTERNATIVE" /> </intent-filter> </activity> </application> </manifest> 

5 error log error

 02-10 21:04:45.203: E/AndroidRuntime(1107): FATAL EXCEPTION: main 02-10 21:04:45.203: E/AndroidRuntime(1107): java.lang.RuntimeException: Unable to start activity ComponentInfo{org.th.mybook/org.th.mybook.MainTabPanel}: java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{org.th.mybook/org.th.mybook.MyBookActivity}: java.lang.NullPointerException 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.ActivityThread.access$2300(ActivityThread.java:125) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.os.Handler.dispatchMessage(Handler.java:99) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.os.Looper.loop(Looper.java:123) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.ActivityThread.main(ActivityThread.java:4627) 02-10 21:04:45.203: E/AndroidRuntime(1107): at java.lang.reflect.Method.invokeNative(Native Method) 02-10 21:04:45.203: E/AndroidRuntime(1107): at java.lang.reflect.Method.invoke(Method.java:521) 02-10 21:04:45.203: E/AndroidRuntime(1107): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 02-10 21:04:45.203: E/AndroidRuntime(1107): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 02-10 21:04:45.203: E/AndroidRuntime(1107): at dalvik.system.NativeStart.main(Native Method) 02-10 21:04:45.203: E/AndroidRuntime(1107): Caused by: java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{org.th.mybook/org.th.mybook.MyBookActivity}: java.lang.NullPointerException 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.ActivityThread.startActivityNow(ActivityThread.java:2503) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:651) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.widget.TabHost.setCurrentTab(TabHost.java:323) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.widget.TabHost.addTab(TabHost.java:213) 02-10 21:04:45.203: E/AndroidRuntime(1107): at org.th.mybook.MainTabPanel.onCreate(MainTabPanel.java:30) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627) 02-10 21:04:45.203: E/AndroidRuntime(1107): ... 11 more 02-10 21:04:45.203: E/AndroidRuntime(1107): Caused by: java.lang.NullPointerException 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:100) 02-10 21:04:45.203: E/AndroidRuntime(1107): at org.th.mybook.MyBookActivity.<init>(MyBookActivity.java:16) 02-10 21:04:45.203: E/AndroidRuntime(1107): at java.lang.Class.newInstanceImpl(Native Method) 02-10 21:04:45.203: E/AndroidRuntime(1107): at java.lang.Class.newInstance(Class.java:1429) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.Instrumentation.newActivity(Instrumentation.java:1021) 02-10 21:04:45.203: E/AndroidRuntime(1107): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577) 02-10 21:04:45.203: E/AndroidRuntime(1107): ... 20 more 

please help me and tell me what I missed by comparing this code with my old one and I can’t find anything considering

6) my book activity

 public class MyBookActivity extends Activity { java.text.DateFormat dateFormat = android.text.format.DateFormat.getDateFormat(getApplicationContext()); @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); DigitalClock clock = (DigitalClock) findViewById(R.id.digitalClock1); final TextView date = (TextView) findViewById(R.id.textView1); date.setText(dateFormat.format(new Date())); TextWatcher watcher = new TextWatcher() { @Override public void afterTextChanged(Editable s) { } @Override public void beforeTextChanged(CharSequence s, int start, int count, int after) { } @Override public void onTextChanged(CharSequence s, int start, int before, int count) { if (s.toString().startsWith("00:00:00") || s.toString().startsWith("12:00:00")) { date.setText(dateFormat.format(new Date())); } } }; clock.addTextChangedListener(watcher); } } 

7) main.xml layout → for my book activity

 <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:gravity="right" android:orientation="horizontal" > <LinearLayout android:id="@+id/DatePanel1" android:layout_width="wrap_content" android:layout_height="wrap_content" > <TextView android:id="@+id/textView1" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginRight="@dimen/space" android:layout_weight="1" android:text="TextView" /> <DigitalClock android:id="@+id/digitalClock1" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:text="DigitalClock" /> </LinearLayout> </LinearLayout> 

Answer 1

It was my own stupidity:

 java.text.DateFormat dateFormat = android.text.format.DateFormat.getDateFormat(getApplicationContext()); 

Setting this onCreate() my problem.

Answer 2

  <activity android:name="MyBookActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.ALTERNATIVE" /> </intent-filter> </activity> 

Where is your point in front of MyBookActivity?

Answer 3

Your Manifest should change, as this activity name should be indicated as ".YourActivityname"

 <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.th.mybook" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="8" android:targetSdkVersion="8" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:name=".MainTabPanel" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name=".MyBookActivity" > </activity> </application> 

Answer 4

I had the same problem, I cleaned and rebuilt the project, and it worked.

Answer 5

Dear You used two major installations in your manifest. Take only one action as a trigger: your manifest activity:

 <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.th.mybook" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="8" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:name=".MainTabPanel" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name="MyBookActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.ALTERNATIVE" /> </intent-filter> </activity> </application> </manifest> 

now it will write code (I made your “MyActivityBook” your default launcher. Copy and paste it into your manifest.

 <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.th.mybook" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="8" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:name=".MainTabPanel" android:label="@string/app_name" > </activity> <activity android:name="MyBookActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest> 

and the second error may be if you copy the old code and then update com.example.packagename.FILE_NAME

hope it works!