CODEWITHSUNDEEP
androidandroid-activity
ARIF MAHMUD RANA
ARIF MAHMUD RANA

Reputation: 5186

Android activity error

I am newbie in android. In android I trying to run a simple work. From my main.xml(http://pastebin.com/Mhgmpj4w) I have one button( my main.java(http://pastebin.com/b5irLVTc) ) it will switch to another activity the second.xml(http://pastebin.com/F92VxSEZ) where it will show some text ( my second.java(http://pastebin.com/MR3L5WXL) ) but there are some errors(http://pastebin.com/KH2wDh7b). I am a newbie please help me.

main.xml:

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

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button" />

</LinearLayout>

main.java:

    package com.rana.activities;

    import android.app.Activity;
    import android.content.Intent;
    import android.os.Bundle;
    import android.view.View;
    import android.view.View.OnClickListener;
    import android.widget.Button;

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

            Button b = (Button) findViewById(android.R.id.button1);
            b.setOnClickListener(new OnClickListener() {

                public void onClick(View v) {
                    startActivity(new Intent(Main.this, Second.class));
                }
            });
        }
    }

second.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" >

        <TextView
            android:id="@+id/textView1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="This is the second activity" />

    </LinearLayout>

second.java:

    package com.rana.activities;

    import android.app.Activity;
    import android.os.Bundle;

    public class Second extends Activity {

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            // TODO Auto-generated method stub
            super.onCreate(savedInstanceState);
            setContentView(R.layout.second);
        }

    }

logcat:

    10-29 19:19:25.377: D/AndroidRuntime(859): Shutting down VM
    10-29 19:19:25.377: W/dalvikvm(859): threadid=1: thread exiting with uncaught exception (group=0x40015560)
    10-29 19:19:25.397: E/AndroidRuntime(859): FATAL EXCEPTION: main
    10-29 19:19:25.397: E/AndroidRuntime(859): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.rana.activities/com.rana.activities.Main}: java.lang.NullPointerException
    10-29 19:19:25.397: E/AndroidRuntime(859):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at android.os.Handler.dispatchMessage(Handler.java:99)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at android.os.Looper.loop(Looper.java:123)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at android.app.ActivityThread.main(ActivityThread.java:3683)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at java.lang.reflect.Method.invokeNative(Native Method)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at java.lang.reflect.Method.invoke(Method.java:507)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at dalvik.system.NativeStart.main(Native Method)
    10-29 19:19:25.397: E/AndroidRuntime(859): Caused by: java.lang.NullPointerException
    10-29 19:19:25.397: E/AndroidRuntime(859):  at com.rana.activities.Main.onCreate(Main.java:18)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
    10-29 19:19:25.397: E/AndroidRuntime(859):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
    10-29 19:19:25.397: E/AndroidRuntime(859):  ... 11 more
    <-------LogCat------------------->

Upvotes: 0

Views: 2819

Answers (4)

Maheshvirus
Maheshvirus

Reputation: 7553

You should make entry of second.java file into the android Manifest file. like this

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.sevenapp"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.sevenapp.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name="second"></activity>///Make entry here
    </application>

</manifest>

Upvotes: 0

Anil Shrestha
Anil Shrestha

Reputation: 51

Button b = (Button) findViewById(R.id.button1);
b.setOnClickListener(new View.OnClickListener() {

@Override
public void onClick(View v) {

    Toast.makeText(MainActivity.this,"You clicked it!",Toast.LENGTH_LONG).show();
    startActivity(new Intent(MainActivity.this,Second.class));


    }

} );

Hope that beginners strucking at this kind of problem will feel great.

Upvotes: 0

Dinesh Prajapati
Dinesh Prajapati

Reputation: 9520

Replace android.R.id.button1 this with R.id.button1 and import your own package R class in main.java. It will solve the problem. In this way it will allocated the memory from your application and hence it will not search for the global resouces

Upvotes: 8

Lasse Samson
Lasse Samson

Reputation: 1752

Just to help you debug your Android applications in the future the interesting lines of error are these:

10-29 19:19:25.397: E/AndroidRuntime(859): Caused by: java.lang.NullPointerException
10-29 19:19:25.397: E/AndroidRuntime(859):      at com.rana.activities.Main.onCreate(Main.java:18)

In line 18 of your Main.java file we have b.setOnClickListener(new OnClickListener() and a NullPointerException. This exception is caused by line 17 in your code with Button b = (Button) findViewById(android.R.id.button1);

As Drax mentioned the error can easily be solved by supplying the correct id.

Good luck with your future developing in Android I hope you'll find it fun :-)

Upvotes: 1

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