不幸的是，应用程序已停止在模拟器中工作

Question

I got this error while running my app in emulator:

Unfortunately App has stopped

My App is music player app with simple functionality.

All other apps are running perfectly in the same emulator. Only this app is not working.

After looking at the log, I also see this error:

09-10 16:01:28.460: E/AndroidRuntime(1200): Caused by: java.lang.InstantiationException: can't instantiate class com.example.musicplayer.MainActivity

Code for MainActivity.java :

package com.example.musicplayer;

import com.example.musicplayer.R;

//import com.example.musicplayer.secondscreen;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.SeekBar;
import android.widget.TextView;

public abstract class MainActivity extends Activity implements OnClickListener {
    SeekBar seek_bar;
    Button play_button, pause_button;
    MediaPlayer player;
    TextView text_shown;
    Handler seekHandler = new Handler();
    ImageButton button;

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

        getInit();
        seekUpdation();
        addListenerOnButton();
    }

 //Function for Button press to change the screen

    public void addListenerOnButton() {

        final Context context = this;

        button = (ImageButton) findViewById(R.id.btnForward);

        button.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {

                Intent intent = new Intent(context, SecondScreen.class);
                            startActivity(intent);   

            }

        });

    }

    //function for play/pause Audio

    public void getInit() {
        seek_bar = (SeekBar) findViewById(R.id.seek_bar);
        play_button = (Button) findViewById(R.id.btnPlay);
        pause_button = (Button) findViewById(R.id.btnPause);
        //text_shown = (TextView) findViewById(R.id.text_shown);
        play_button.setOnClickListener(this);
        pause_button.setOnClickListener(this);
        player = MediaPlayer.create(this, R.raw.fat); //ye wo Audio file hai jo chalarae
        seek_bar.setMax(player.getDuration());

    }

    Runnable run = new Runnable() {

        @Override
        public void run() {
            seekUpdation();
        }
    };

    // function for update seekbar

    public void seekUpdation() {
        seek_bar.setProgress(player.getCurrentPosition());
        seekHandler.postDelayed(run, 1000);
    }

Code for activity_main.xml :

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

    <!-- Player Header -->
    <LinearLayout 
       android:id="@+id/player_header_bg"
        android:layout_width="fill_parent"
        android:layout_height="60dip"

        android:layout_alignParentTop="true"
        android:paddingLeft="5dp"
        android:paddingRight="5dp">

        <!-- Audio Title -->
        <TextView 
            android:id="@+id/audioTitle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:textColor="#04b3d2"
            android:textSize="16dp"
            android:paddingLeft="10dp"
            android:textStyle="bold"
            android:text="1"
            android:layout_marginTop="10dp"/>

        <!-- Playlist button -->
        <ImageButton 
            android:id="@+id/btnPlaylist"
            android:layout_width="wrap_content"
            android:layout_height="fill_parent"
            android:src="@drawable/btn_playlist"
            android:background="@null"/>
    </LinearLayout>

    <!-- Sabak  Image -->

    <LinearLayout
        android:id="@+id/AudioThumbnail"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"

        android:gravity="center"
        android:paddingBottom="10dp"
        android:paddingTop="10dp" >

        <ImageView
            android:layout_width="292dp"
            android:layout_height="283dp"
            android:src="@drawable/fatiha" />

    </LinearLayout>

    <!-- Player Footer -->
    <LinearLayout 
        android:id="@+id/player_footer_bg"
        android:layout_width="fill_parent"
        android:layout_height="100dp"
        android:layout_alignParentBottom="true"

        android:gravity="center">

        <!-- Player Buttons -->
        <LinearLayout 
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:gravity="center_vertical"

            android:paddingLeft="10dp"
            android:paddingRight="10dp">
            <!-- Previous Button -->
            <!-- Backward Button -->
            <ImageButton 
                android:id="@+id/btnBackward"
                android:src="@drawable/btn_backward"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@null"/>

            <!-- Pause Button -->


            <ImageButton
                android:id="@+id/btnPause"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@null"
                android:enabled="false"
                android:gravity="center"
                android:src="@drawable/btn_pause" />


<!-- Play Button -->            
<ImageButton
                android:id="@+id/btnPlay"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@null"
                android:src="@drawable/btn_play" 
               android:gravity="center" />

  <!-- Forward Button -->

            <ImageButton
                android:id="@+id/btnForward"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:background="@null"
                android:src="@drawable/btn_forward" />
        </LinearLayout>
    </LinearLayout>

    <!-- SABAK Progress Bar/Seek bar -->
    <SeekBar
               android:id="@+id/seek_bar"
             android:layout_width="fill_parent"
             android:layout_height="wrap_content"
             android:layout_marginRight="20dp" 
             android:layout_marginLeft="20dp"
             android:layout_marginBottom="20dp"
             android:layout_above="@id/player_footer_bg"
             android:thumb="@drawable/seek_handler"
             android:progressDrawable="@drawable/seekbar_progress"
             android:paddingLeft="6dp"
             android:paddingRight="6dp"/>

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_above="@+id/audioProgressBar"
        android:gravity="center" >

 </LinearLayout>

</RelativeLayout>

Code For Manifest.xml :

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

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.musicplayer.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>
    </application>

LogCat :

09-10 16:01:28.250: D/dalvikvm(1200): newInstance failed: p0 i0 [0 a1
09-10 16:01:28.250: D/AndroidRuntime(1200): Shutting down VM
09-10 16:01:28.260: W/dalvikvm(1200): threadid=1: thread exiting with uncaught exception (group=0xb3b0bb90)
09-10 16:01:28.460: E/AndroidRuntime(1200): FATAL EXCEPTION: main
09-10 16:01:28.460: E/AndroidRuntime(1200): Process: com.example.musicplayer, PID: 1200
09-10 16:01:28.460: E/AndroidRuntime(1200): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.musicplayer/com.example.musicplayer.MainActivity}: java.lang.InstantiationException: can't instantiate class com.example.musicplayer.MainActivity
09-10 16:01:28.460: E/AndroidRuntime(1200):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2102)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at android.app.ActivityThread.access$700(ActivityThread.java:135)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at android.os.Handler.dispatchMessage(Handler.java:102)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at android.os.Looper.loop(Looper.java:137)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at android.app.ActivityThread.main(ActivityThread.java:4998)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at java.lang.reflect.Method.invokeNative(Native Method)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at java.lang.reflect.Method.invoke(Method.java:515)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at dalvik.system.NativeStart.main(Native Method)
09-10 16:01:28.460: E/AndroidRuntime(1200): Caused by: java.lang.InstantiationException: can't instantiate class com.example.musicplayer.MainActivity
09-10 16:01:28.460: E/AndroidRuntime(1200):     at java.lang.Class.newInstanceImpl(Native Method)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at java.lang.Class.newInstance(Class.java:1208)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
09-10 16:01:28.460: E/AndroidRuntime(1200):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2093)
09-10 16:01:28.460: E/AndroidRuntime(1200):     ... 11 more

Answer 1

java.lang.InstantiationException: can't instantiate class com.example.musicplayer.MainActivity

Your MainActivity is abstract and abstract classes cannot be instantiated. Remove the abstract keyword from the class declaration.

Answer 2

You are trying to start the SecondScreen activity which is not declared on the Manifest File .

<activity android:name="com.example.musicplayer.SecondScreen" /> 

For more details about how to switch between activities and pass data between them , you can follow this tutorial : http://www.android-ios-tutorials.com/117/how-to-switch-between-different-activities-in-android/

EDIT :

The activity MainActivity should not be abstract ; remove the abstract from the declaration :

public class MainActivity extends Activity ...