Question

Hi i am making an app in which I am allowing user to add a reminder, but while i do click on Add New button getting Error – Unfortunately Reminderer has Stopped.

AddTaskActivity.java Code:

  public class AddTaskActivity extends Activity {
Task mTask;
Handler mHandler = new AddHandler();

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.add_task);

Button add = (Button) this.findViewById(R.id.submit);
add.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View arg0) {
    GrammarParser parser = new GrammarParser();
    parser.setAndroidContext(AddTaskActivity.this);
    EditText text = (EditText) findViewById(R.id.add_task);
    String input = text.getText().toString();
    mTask = parser.parse(input);
    String output = mTask.toString();
    TextView log = (TextView) findViewById(R.id.log_cat);
    log.setText(output);
    }

});

Button save = (Button) findViewById(R.id.save);
save.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View arg0) {
    if (mTask != null)
        DatabaseInterface.addTask(AddTaskActivity.this, mHandler,
            mTask);

    }

});

Button cancel = (Button) findViewById(R.id.cancel);
cancel.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View arg0) {
    finish();

    }

});

}

add_task.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >

    <EditText
        android:id="@+id/add_task"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="2"
        android:ems="10"
        android:inputType="text" >

        <requestFocus />
    </EditText>

    <Button
        android:id="@+id/submit"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="@string/add_new_task" />
</LinearLayout>

<TextView
    android:id="@+id/log_cat"
    android:layout_width="wrap_content"
    android:layout_height="0dip"
    android:layout_weight="1"
    android:text="@string/no_task"
    android:textAppearance="?android:attr/textAppearanceMedium" />

   <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >

    <Button
        android:id="@+id/save"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="@string/save" />

    <Button
        android:id="@+id/cancel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="@string/cancel" />
</LinearLayout>

</LinearLayout>

strings.xml:

<resources>

<string name="hello">Hello World, RemindererActivity!</string>
<string name="app_name">Reminderer</string>
<string name="hello_world">Hello world</string>
<string name="add_new_task">Add new</string>
<string name="submit">Submit</string>
<string name="no_task">Sample tasks:\n
    buy eggs\n
    buy eggs 8pm\n
    buy eggs Monday 9am\n
    buy eggs July 1\n
    buy eggs next Monday\n
    buy eggs 8pm repeats daily</string>
<string name="due_now">These task(s) are due now:</string>
<string name="dismiss">Dismiss</string>
<string name="snooze">Snooze</string>
<string name="save">Save</string>
<string name="cancel">Cancel</string>

Logcat Says:

    01-11 16:05:01.252: E/AndroidRuntime(943): FATAL EXCEPTION: main
01-11 16:05:01.252: E/AndroidRuntime(943): java.lang.NullPointerException
01-11 16:05:01.252: E/AndroidRuntime(943):  at com.frankandrobot.reminderer.AddTaskActivity$1.onClick(AddTaskActivity.java:39)
01-11 16:05:01.252: E/AndroidRuntime(943):  at android.view.View.performClick(View.java:4202)
01-11 16:05:01.252: E/AndroidRuntime(943):  at android.view.View$PerformClick.run(View.java:17340)
01-11 16:05:01.252: E/AndroidRuntime(943):  at android.os.Handler.handleCallback(Handler.java:725)
01-11 16:05:01.252: E/AndroidRuntime(943):  at android.os.Handler.dispatchMessage(Handler.java:92)
01-11 16:05:01.252: E/AndroidRuntime(943):  at android.os.Looper.loop(Looper.java:137)
01-11 16:05:01.252: E/AndroidRuntime(943):  at android.app.ActivityThread.main(ActivityThread.java:5039)
01-11 16:05:01.252: E/AndroidRuntime(943):  at java.lang.reflect.Method.invokeNative(Native Method)
01-11 16:05:01.252: E/AndroidRuntime(943):  at java.lang.reflect.Method.invoke(Method.java:511)
01-11 16:05:01.252: E/AndroidRuntime(943):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
01-11 16:05:01.252: E/AndroidRuntime(943):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
01-11 16:05:01.252: E/AndroidRuntime(943):  at dalvik.system.NativeStart.main(Native Method)

Answer 1

It’s difficult to tell which line in onClick() is causing the NPE, as you haven’t provided line numbers. You need to perform more error checking in your code, and use assert() more often:

@Override
public void onClick(View arg0) {
    GrammarParser parser = new GrammarParser();
    parser.setAndroidContext(AddTaskActivity.this);

    EditText text = (EditText) findViewById(R.id.add_task);
    assert(text != null);
    String input = text.getText().toString();
    mTask = parser.parse(input);
    if (mTask != null) {
        String output = mTask.toString();
        TextView log = (TextView) findViewById(R.id.log_cat);
        assert(log != null);
        log.setText(output);
    }
    else {
        Log.e(TAG, "Failed to parse text");
    }
}