I currently develop an application which contains a custom ListView. I developed a custom array adapter. I think my app crashes here: ListView DirectoryView = (ListView) findViewById(R.id.fileListView); So i think the error is in the activity_main.xml: <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="fill_parent" android:layout_height="fill_parent" > <ListView android:id="@+id/fileListView" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1" > </ListView> Here is my LogCat: 09-09 11:19:21.254: E/Trace(1152): error opening trace file: No such file or directory (2) 09-09 11:19:21.484: D/AndroidRuntime(1152): Shutting down VM 09-09 11:19:21.484: W/dalvikvm(1152): threadid=1: thread exiting with uncaught exception (group=0x40a13300) 09-09 11:19:21.504: E/AndroidRuntime(1152): FATAL EXCEPTION: main 09-09 11:19:21.504: E/AndroidRuntime(1152): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.teamdroid.explorer/com.teamdroid.explorer.MainActivity}: java.lang.NullPointerException 09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059) 09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread.access$600(ActivityThread.java:130) 09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 09-09 11:19:21.504: E/AndroidRuntime(1152): at android.os.Handler.dispatchMessage(Handler.java:99) 09-09 11:19:21.504: E/AndroidRuntime(1152): at android.os.Looper.loop(Looper.java:137) 09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread.main(ActivityThread.java:4745) 09-09 11:19:21.504: E/AndroidRuntime(1152): at java.lang.reflect.Method.invokeNative(Native Method) 09-09 11:19:21.504: E/AndroidRuntime(1152): at java.lang.reflect.Method.invoke(Method.java:511) 09-09 11:19:21.504: E/AndroidRuntime(1152): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 09-09 11:19:21.504: E/AndroidRuntime(1152): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 09-09 11:19:21.504: E/AndroidRuntime(1152): at dalvik.system.NativeStart.main(Native Method) 09-09 11:19:21.504: E/AndroidRuntime(1152): Caused by: java.lang.NullPointerException 09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.Activity.findViewById(Activity.java:1825) 09-09 11:19:21.504: E/AndroidRuntime(1152): at com.teamdroid.explorer.listDirectory.getDirectory(listDirectory.java:20) 09-09 11:19:21.504: E/AndroidRuntime(1152): at com.teamdroid.explorer.MainActivity.onCreate(MainActivity.java:33) 09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.Activity.performCreate(Activity.java:5008) 09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079) 09-09 11:19:21.504: E/AndroidRuntime(1152): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023) 09-09 11:19:21.504: E/AndroidRuntime(1152): ... 11 more Please can you help me. I am searching this error for 2 day. thanks!