Error with custom OnClickListener class

Question

The app force closes without even starting, see below for logcat info and (app works when 3 lines below are commented out)

• also says in the LogCat there is an issue with NullPointerException but I don't know where and how to solve it.

XML file:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.figurehowtodo.MainActivity$PlaceholderFragment" >

<TextView
    android:id="@+id/produceText1"
    android:layout_width="280dp"
    android:layout_height="50dp"
    android:text="@string/hello_world"
    />

<Button
    android:id="@+id/myFirstButton"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="ClickMe1" />

<Button
    android:id="@+id/mySecondButton"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="ClickMe2" />

<Button
    android:id="@+id/myThirdButton"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="ClickMe3" />

</LinearLayout>

MainActivity.java

package com.example.figurehowtodo;

import android.app.Activity;
import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {

Button myFirstButton;
Button mySecondButton;
Button myThirdButton;
TextView tvView;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.fragment_main);

    myFirstButton = (Button) findViewById(R.id.myFirstButton);
    mySecondButton = (Button) findViewById(R.id.mySecondButton);
    myThirdButton = (Button) findViewById(R.id.myThirdButton);

    tvView = (TextView) findViewById(R.id.produceText1);

    //if (tvView == null) { Log.w("", "TextView is null"); }

If I comment out the bottom three lines my app runs (but without any button functionality). I think the "new" might have something to do with it?

myFirstButton.setOnClickListener(new MyOwnOnClickListener(tvView, "myFirstButton"));
mySecondButton.setOnClickListener(new MyOwnOnClickListener(tvView, "mySecondButton"));
myThirdButton.setOnClickListener(new MyOwnOnClickListener(tvView, "myThirdButton"));

MyOwnOnClickListner.java

package com.example.figurehowtodo;

import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class MyOwnOnClickListener extends Activity implements OnClickListener{
    //int id; //comment line out in order to make it work
    //TextView id3;

    /* 
    *
    *MainActivity caller;
    *public MyOwnOnClickListener() {
    *€  addiTion();
    *   IGNORE THIS BIT
    *} 
    *
    */

    TextView outputBoxId;
    String re_id_button_name;

    Button myFirstButton;
    Button mySecondButton;
    Button myThirdButton;
    TextView tvView3;

    public MyOwnOnClickListener(TextView id2, String id) {
        this.outputBoxId = id2;
        this.re_id_button_name = id;

        myFirstButton = (Button) findViewById(R.id.myFirstButton);
        mySecondButton = (Button) findViewById(R.id.mySecondButton);
        myThirdButton = (Button) findViewById(R.id.myThirdButton);
    }

    public void onClick(View re_id_button_name) {
        //tvView3 = (TextView) findViewById(R.id.produceText1);
        outputBoxId.setText("it worked!!!");
    }

    /*
     * -------IGNORE---------
    if(re_id_button_name.equals(myFirstButton)){
        addiTion();
    }else{return;}

    public void addiTion(){
        //id = v.getId(); //comment line out in order to make it work

        outputBoxId.setText("YOU CLICKED THE FIRST BUTTON!");
    }
    -------IGNORE---------*/
}

LogCat:

03-28 21:56:24.388: E/AndroidRuntime(1256): FATAL EXCEPTION: main
03-28 21:56:24.388: E/AndroidRuntime(1256): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.figurehowtodo/com.example.figurehowtodo.MainActivity}: java.lang.NullPointerException
03-28 21:56:24.388: E/AndroidRuntime(1256):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at android.os.Looper.loop(Looper.java:123)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at android.app.ActivityThread.main(ActivityThread.java:3683)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at java.lang.reflect.Method.invokeNative(Native Method)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at java.lang.reflect.Method.invoke(Method.java:507)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at dalvik.system.NativeStart.main(Native Method)
03-28 21:56:24.388: E/AndroidRuntime(1256): Caused by: java.lang.NullPointerException
03-28 21:56:24.388: E/AndroidRuntime(1256):     at android.app.Activity.findViewById(Activity.java:1647)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at com.example.figurehowtodo.MyOwnOnClickListener.<init>(MyOwnOnClickListener.java:31)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at com.example.figurehowtodo.MainActivity.onCreate(MainActivity.java:25)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
03-28 21:56:24.388: E/AndroidRuntime(1256):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
03-28 21:56:24.388: E/AndroidRuntime(1256):     ... 11 more
03-28 21:56:24.408: W/ActivityManager(62):   Force finishing activity com.example.figurehowtodo/.MainActivity
03-28 21:56:24.917: W/ActivityManager(62): Activity pause timeout for HistoryRecord{407eda90 com.example.figurehowtodo/.MainActivity}
03-28 21:56:30.757: D/dalvikvm(233): GC_EXPLICIT freed 8K, 55% free 2597K/5703K, external 1625K/2137K, paused 53ms

Answer 1

The main problem here is that your custom OnClickListener shouldn't extends Activity because it isn't an Activity. And such, it doesn't have the layout that holds the ids of the Views you are trying to inflate.

This is why it crashes because you get a NPE when trying to set the listener on those Views. You need to set the listeners on them in your actual Activity where you inflate the layout with findViewById().

So, instead of having something like

myBtn.setOnClickListener(new View.OnClickListener());

you would have

myBtn.setOnClickListener(new MyOwnOnClickListener());

Edit

Try this, use the Context from the View passed in to get the other View. I'm not positive this will work and I don't have time to test it at this moment but let's see.

public MyOwnOnClickListener(TextView id2, String id) {

    myFirstButton = (Button) id2.getContext().findViewById(R.id.myFirstButton);
}

Answer 2

Simple write

        Button myFirstButton = (Button) findViewById(R.id.myFirstButton);
        myFirstButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                // Perform action on click   

            }
        });

And also do same for other buttons.