Android null pointer error with button

Question

I am having trouble trying to make a simple app that is a portfolio. Depending on what button you click I want to load the next activity with the content filled in and I want the color of this little subheader bar to change to the color of the button on the main page. I tried to achieve this with a variable called webColor, to see if I can get it to work with 1 button first before I make it a variable for all of them. The web link is a color code that the variable should change to, it looks like it should work but then when I run it I get the following.

   05-18 23:07:08.573    1554-1554/com.dredaydesigns.dredaycreativeportfolio     D/dalvikvm﹕ Late-enabling CheckJNI
    05-18 23:07:08.917    1554-1554/com.dredaydesigns.dredaycreativeportfolio     I/dalvikvm﹕ Could not find method     android.content.res.TypedArray.getChangingConfigurations, referenced from method         android.support.v7.internal.widget.TintTypedArray.getChangingConfigurations
    05-18 23:07:08.917    1554-1554/com.dredaydesigns.dredaycreativeportfolio     W/dalvikvm﹕ VFY: unable to resolve virtual method 406:     Landroid/content/res/TypedArray;.getChangingConfigurations ()I
    05-18 23:07:08.953    1554-1554/com.dredaydesigns.dredaycreativeportfolio     D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x0002    
    05-18 23:07:08.953    1554-1554/com.dredaydesigns.dredaycreativeportfolio     I/dalvikvm﹕ Could not find method android.content.res.TypedArray.getType,     referenced from method android.support.v7.internal.widget.TintTypedArray.getType
    05-18 23:07:08.953    1554-1554/com.dredaydesigns.dredaycreativeportfolio      W/dalvikvm﹕ VFY: unable to resolve virtual method 428: Landroid/content/res/TypedArray;.getType (I)I
05-18 23:07:08.953    1554-1554/com.dredaydesigns.dredaycreativeportfolio   D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x0002
     05-18 23:07:08.969    1554-1554/com.dredaydesigns.dredaycreativeportfolio D/AndroidRuntime﹕ Shutting down VM
     05-18 23:07:08.969    1554-1554/com.dredaydesigns.dredaycreativeportfolio W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xa4ce1b20)
05-18 23:07:08.969    1554-1554/com.dredaydesigns.dredaycreativeportfolio E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.dredaydesigns.dredaycreativeportfolio, PID: 1554
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dredaydesigns.dredaycreativeportfolio/com.dredaydesigns.dredaycreativeportfolio.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5001)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.dredaydesigns.dredaycreativeportfolio.MainActivity.onCreate(MainActivity.java:22)
            at android.app.Activity.performCreate(Activity.java:5231)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5001)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at     com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)








package com.dredaydesigns.dredaycreativeportfolio;
import android.R;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.widget.Button;
public class MainActivity extends ActionBarActivity {
String webColor;
Button webButton;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list_item);

    webButton = (Button) findViewById(R.id.button1);

    webButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            String webColor = webButton.getText().toString();
            Intent goToNext = new     Intent(MainActivity.this,content_activity.class);
            goToNext.putExtra(webColor,"#C41E72");
            startActivity(goToNext);

        }
    });


}

Answer 1

Take a look at your codes specifically as explained by the error codes:

 Caused by: java.lang.NullPointerException
        at com.dredaydesigns.dredaycreativeportfolio.MainActivity.onCreate(MainActivity.java:22)

If you examine it closely, you will see the error is on MainActivity.java line 22 . What is on that line? Check if it is already initialised.

Answer 2

public class MainActivity extends ActionBarActivity {
String webColor;
Button webButton;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list_item);

    webButton = (Button) findViewById(R.id.button1);

    webButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            String webColor = webButton.getText().toString();
            Intent goToNext = new     Intent(MainActivity.this,content_activity.class);
            goToNext.putExtra(webColor,"#C41E72");
            startActivity(goToNext);

        }
    });


}

to replace this.

public class MainActivity extends **Activity** {
String webColor;
Button webButton;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list_item);

    webButton = (Button) findViewById(R.id.button1);
    webButton.setOnClickListener(new OnClickListener() {
        @Override
        **public void onClick(View v) {
            webColor= webButton.getText().toString();
            Intent goToNext = new         Intent(MainActivity.this,SecondClassName.class);
            goToNext.putExtra(webColor,"#C41E72");
            startActivity(goToNext);
        }
    });


}

and Sure about you enter activity details in manifest ?

Answer 3

setContentView(R.layout.activity_list_item);

webButton = (Button) findViewById(R.id.button1);

webButton.setOnClickListener

I think, there is no button which its id = button1 in layout file "activity_list_item", please make sure you are using correct layout file. Line 22 cause NullPointerException may be "webButton.setOnClickListener", because activity can not find webButton here.