具有SeekBar和MediaPlayer的java.lang.NullPointerException

Question

I'm new in Android and I'm trying to run a seekbar while playing audio.

I'm getting the error "Unable to start activity ComponentInfo: java.lang.NullPointerException" when I try to set the range of the progress bar with "setMax".

This is my code:

public class PlayerActivity extends Activity {
    private MediaPlayer mPlayer;
    private SeekBar mSeekBar;


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

        if (savedInstanceState == null) {
            getFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }

        initVariables();
    }

    public void initVariables(){
        mPlayer = new MediaPlayer();
        mPlayer = MediaPlayer.create(this, R.raw.raunchy);
        mPlayer.setOnCompletionListener(onCompletion);

        mSeekBar = (SeekBar) findViewById(R.id.seekBar1);
        mSeekBar.setMax(mPlayer.getDuration());
    }

    private MediaPlayer.OnCompletionListener onCompletion = new MediaPlayer.OnCompletionListener() {
        @Override
        public void onCompletion(MediaPlayer mPlayer) {
            mPlayer.release();
            Log.d("FINAL", "CORRECTO");
        }
    };

    public void playOrPause(View v) {
        if (!mPlayer.isPlaying()) {
            mPlayer.start();
        } else {
            mPlayer.pause();
        }
        mHandler.postDelayed(mRunnable, 100);
    }

    private Handler mHandler = new Handler();
    private Runnable mRunnable = new Runnable() {
        @Override
        public void run() {
            mSeekBar.setMax(mPlayer.getDuration());
            if(mPlayer.isPlaying()){
                int mCurrentPosition = mPlayer.getCurrentPosition() / 1000;
                mSeekBar.setProgress(mCurrentPosition);
            }
            mHandler.postDelayed(this, 1000);
        }
    };

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_player,
                    container, false);
            return rootView;
        }
    }

}

This is my Fragment.

<RelativeLayout 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: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.jgutierrezgil.bmusic.MainActivity$PlaceholderFragment" >

<Button
    android:id="@+id/button_play"
    style="?android:attr/buttonStyleSmall"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    android:text="@string/play_button"
    android:onClick="playOrPause" />

<Button
    android:id="@+id/button_stop"
    style="?android:attr/buttonStyleSmall"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_toRightOf="@+id/button_play"
    android:text="@string/stop_button"
    android:onClick="stop" />

<Button
    android:id="@+id/button1"
    style="?android:attr/buttonStyleSmall"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_toLeftOf="@+id/button_play"
    android:text="Button" />

<SeekBar
    android:id="@+id/seekBar1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_above="@+id/button_play"
    android:layout_centerHorizontal="true"
    android:layout_marginBottom="14dp" />

<TextView
    android:id="@+id/startTimeField"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_above="@+id/button1"
    android:layout_alignLeft="@+id/seekBar1"
    android:text="Small Text"
    android:textAppearance="?android:attr/textAppearanceSmall" />

<TextView
    android:id="@+id/endTimeField"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_above="@+id/button_stop"
    android:layout_alignRight="@+id/seekBar1"
    android:text="Small Text"
    android:textAppearance="?android:attr/textAppearanceSmall" />

<Button
    android:id="@+id/library"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/Player"
    android:layout_alignBottom="@+id/Player"
    android:layout_alignRight="@+id/seekBar1"
    android:layout_toRightOf="@+id/button_play"
    android:text="@string/library_button"
    android:onClick="toLibrary" />

<Button
    android:id="@+id/Player"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/seekBar1"
    android:layout_alignParentTop="true"
    android:layout_toLeftOf="@+id/button_play"
    android:clickable="false"
    android:focusable="false"
    android:longClickable="false"
    android:text="@string/player_button" />

And this the Logcat.

    06-03 22:04:47.023: E/AndroidRuntime(1191): FATAL EXCEPTION: main
06-03 22:04:47.023: E/AndroidRuntime(1191): Process: com.jgutierrezgil.bmusic, PID: 1191
06-03 22:04:47.023: E/AndroidRuntime(1191): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.jgutierrezgil.bmusic/com.jgutierrezgil.bmusic.PlayerActivity}: java.lang.NullPointerException
06-03 22:04:47.023: E/AndroidRuntime(1191):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at android.os.Handler.dispatchMessage(Handler.java:102)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at android.os.Looper.loop(Looper.java:136)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at android.app.ActivityThread.main(ActivityThread.java:5017)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at java.lang.reflect.Method.invokeNative(Native Method)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at java.lang.reflect.Method.invoke(Method.java:515)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at dalvik.system.NativeStart.main(Native Method)
06-03 22:04:47.023: E/AndroidRuntime(1191): Caused by: java.lang.NullPointerException
06-03 22:04:47.023: E/AndroidRuntime(1191):     at com.jgutierrezgil.bmusic.PlayerActivity.initVariables(PlayerActivity.java:41)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at com.jgutierrezgil.bmusic.PlayerActivity.onCreate(PlayerActivity.java:32)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at android.app.Activity.performCreate(Activity.java:5231)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-03 22:04:47.023: E/AndroidRuntime(1191):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
06-03 22:04:47.023: E/AndroidRuntime(1191):     ... 11 more
06-03 22:04:49.193: I/Process(1191): Sending signal. PID: 1191 SIG: 9

Manifest

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

    <uses-sdk
        android:minSdkVersion="15"
        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.jgutierrezgil.bmusic.PlayerActivity"
            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>

</manifest>

Thank's in advance for your help.

Answer 1

You add the fragment with a transaction, then you immediately try to find the seekbar view before it is in the view hierarchy. The seekbar is not found, and is therefore null, so you get the NullPointerException when calling setMax on it.

You should remove these two lines from PlayerActivity.onCreate():

    mSeekBar = (SeekBar) findViewById(R.id.seekBar1);
    mSeekBar.setMax(mPlayer.getDuration());

and instead put them in PlaceholderFragment.onCreateView() after inflating the rootView, so you know the seekbar will be found, like this:

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_player,
                container, false);
        mSeekBar = (SeekBar) rootView.findViewById(R.id.seekBar1);
        mSeekBar.setMax(mPlayer.getDuration());
        return rootView;
    }