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POTo Do List Example
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  1. POTo Do List Example
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    copied!<p>I am new to Android App Development and have a small problem.</p> <p>I have tried to follow an example to create a to do list app. However it doesn't work even though I have copied it exactly.</p> <p>It shows no errors when I run it however, a blank screen appears and after a few seconds it closes and says "Unfortunately, ToDoList has stopped."</p> <p>Does anyone know what this problem might be?</p> <p><strong>Code</strong></p> <pre><code> package com.paad.todolist; import java.util.ArrayList; import android.app.Activity; import android.os.Bundle; import android.view.KeyEvent; import android.view.Menu; import android.view.View; import android.widget.ArrayAdapter; import android.widget.EditText; import android.widget.ListView; public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); ListView myListView = (ListView)findViewById(R.id.ListView); final EditText myEditText = (EditText) findViewById(R.id.EditText); final ArrayList&lt;String&gt; todoItems = new ArrayList&lt;String&gt;(); final ArrayAdapter&lt;String&gt; aa; aa = new ArrayAdapter&lt;String&gt; (this,android.R.layout.simple_list_item_1,todoItems); myListView.setAdapter(aa); myEditText.setOnKeyListener(new View.OnKeyListener() { public boolean onKey(View v, int keyCode, KeyEvent event) { if (event.getAction() == KeyEvent.ACTION_DOWN) if ((keyCode == KeyEvent.KEYCODE_DPAD_CENTER) || (keyCode == KeyEvent.KEYCODE_ENTER)) { todoItems.add(0, myEditText.getText().toString()); aa.notifyDataSetChanged(); myEditText.setText(""); return true; } return false; } }); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.activity_main, menu); return true; } } </code></pre> <p><strong>Layout XML File</strong></p> <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt; &lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" &gt; &lt;EditText android:id="@+id/EditText" android:layout_width="match_parent" android:layout_height="wrap_content" android:hint="@string/addItemHint" android:contentDescription="@string/addItemContentDescription" /&gt; &lt;ListView android:id="@+id/ListView" android:layout_width="match_parent" android:layout_height="wrap_content" /&gt; &lt;/LinearLayout&gt; </code></pre> <p>Log:</p> <pre><code>02-10 20:03:53.850: D/AndroidRuntime(24220): Shutting down VM 02-10 20:03:53.850: W/dalvikvm(24220): threadid=1: thread exiting with uncaught exception (group=0x40f0a2a0) 02-10 20:03:53.850: E/AndroidRuntime(24220): FATAL EXCEPTION: main 02-10 20:03:53.850: E/AndroidRuntime(24220): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.paad.todolist/com.paad.todolist.MainActivity}: java.lang.NullPointerException 02-10 20:03:53.850: E/AndroidRuntime(24220): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2100) 02-10 20:03:53.850: E/AndroidRuntime(24220): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125) 02-10 20:03:53.850: E/AndroidRuntime(24220): at android.app.ActivityThread.access$600(ActivityThread.java:140) 02-10 20:03:53.850: E/AndroidRuntime(24220): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227) 02-10 20:03:53.850: E/AndroidRuntime(24220): at android.os.Handler.dispatchMessage(Handler.java:99) 02-10 20:03:53.850: E/AndroidRuntime(24220): at android.os.Looper.loop(Looper.java:137) 02-10 20:03:53.850: E/AndroidRuntime(24220): at android.app.ActivityThread.main(ActivityThread.java:4898) 02-10 20:03:53.850: E/AndroidRuntime(24220): at java.lang.reflect.Method.invokeNative(Native Method) 02-10 20:03:53.850: E/AndroidRuntime(24220): at java.lang.reflect.Method.invoke(Method.java:511) 02-10 20:03:53.850: E/AndroidRuntime(24220): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006) 02-10 20:03:53.850: E/AndroidRuntime(24220): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773) 02-10 20:03:53.850: E/AndroidRuntime(24220): at dalvik.system.NativeStart.main(Native Method) 02-10 20:03:53.850: E/AndroidRuntime(24220): Caused by: java.lang.NullPointerException 02-10 20:03:53.850: E/AndroidRuntime(24220): at com.paad.todolist.MainActivity.onCreate(MainActivity.java:30) 02-10 20:03:53.850: E/AndroidRuntime(24220): at android.app.Activity.performCreate(Activity.java:5206) 02-10 20:03:53.850: E/AndroidRuntime(24220): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1083) 02-10 20:03:53.850: E/AndroidRuntime(24220): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2064) 02-10 20:03:53.850: E/AndroidRuntime(24220): ... 11 more </code></pre>
 

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