如何在Android中从数组中提取字符串？

Question

I have an android app that is a streaming radio. To change the radio stations, there is a drop down menu (based on a spinner) that allows the user to select the radio station and then it will load.

Problem: when I leave it as default, the first channel plays fine ... when I try to chose another station, the app crashes. I am using the new Android Studio.

I think that I am not getting the string for the URL from the array. Can someone help me see what my mistake is??

Here is my code:

import android.annotation.TargetApi;
import android.app.Activity;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.SeekBar;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

import java.io.IOException;
import java.util.concurrent.TimeUnit;

public class AndroidMediaPlayerExample extends Activity {

    private MediaPlayer mediaPlayer;
    public TextView songName, duration;
    private double timeElapsed = 0, finalTime = 0;
    private int forwardTime = 2000, backwardTime = 2000;
    private Handler durationHandler = new Handler();
    private SeekBar seekbar;
    //String url = "http://radio.miraath.net:7000";
    //String url = new String[]{"http://radio.miraath.net:7000", "http://radio.miraath.net:7010", "http://radio.miraath.net:7020", "http://radio.miraath.net:7030","http://radio.miraath.net:7040", };
    String url;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        //set the layout of the Activity
        setContentView(R.layout.activity_main);
        Spinner dropdown = (Spinner)findViewById(R.id.spinner1);
        String[] items = new String[]{"Radio 1: Arabic", "Radio 2: Live Arabic", "Radio 3: Qur'an", "Radio 4: English Radio", "Radio 5: Arabic Radio 2"};
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, items);
        dropdown.setAdapter(adapter);

        //initialize views
        initializeViews();
    }

    public void initializeViews(){
        songName = (TextView) findViewById(R.id.songName);
        mediaPlayer = MediaPlayer.create(this, R.raw.sample_song);
        finalTime = mediaPlayer.getDuration();
        duration = (TextView) findViewById(R.id.songDuration);
        seekbar = (SeekBar) findViewById(R.id.seekBar);
        songName.setText("Radio1 - Miraath.net");

        seekbar.setMax((int) finalTime);
        seekbar.setClickable(false);
    }

    public void onItemSelected(AdapterView<?> parent, View v, int position, long id) {
        mediaPlayer.release();

        switch (position) {

            case 0:
                // Whatever you want to happen when the first item gets selected
                url = "http://radio.miraath.net:7000";
                break;
            case 1:
                // Whatever you want to happen when the second item gets selected
                url = "http://radio.miraath.net:7010";
                break;
            case 2:
                // Whatever you want to happen when the thrid item gets selected
                url = "http://radio.miraath.net:7020";
                break;
            case 3:
                // Whatever you want to happen when the thrid item gets selected
                url = "http://radio.miraath.net:7030";
                break;
            case 4:
                // Whatever you want to happen when the thrid item gets selected
                url = "http://radio.miraath.net:7040";
                break;


        }
    }

    // play mp3 song
    public void play(View view) {
        mediaPlayer = new MediaPlayer();
        mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);

        try {
            mediaPlayer.setDataSource(url);
        } catch (IllegalArgumentException e) {
            Toast.makeText(getApplicationContext(), "You might not set the URI correctly!", Toast.LENGTH_LONG).show();
        } catch (SecurityException e) {
            Toast.makeText(getApplicationContext(), "You might not set the URI correctly!", Toast.LENGTH_LONG).show();
        } catch (IllegalStateException e) {
            Toast.makeText(getApplicationContext(), "You might not set the URI correctly!", Toast.LENGTH_LONG).show();
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            mediaPlayer.prepare();
        } catch (IllegalStateException e) {
            Toast.makeText(getApplicationContext(), "You might not set the URI correctly!", Toast.LENGTH_LONG).show();
        } catch (IOException e) {
            Toast.makeText(getApplicationContext(), "You might not set the URI correctly!", Toast.LENGTH_LONG).show();
        }

        mediaPlayer.start();
        timeElapsed = mediaPlayer.getCurrentPosition();
        seekbar.setProgress((int) timeElapsed);
        durationHandler.postDelayed(updateSeekBarTime, 100);
    }

    //handler to change seekBarTime
    private Runnable updateSeekBarTime = new Runnable() {
        @TargetApi(Build.VERSION_CODES.GINGERBREAD)
        public void run() {
            //get current position
            timeElapsed = mediaPlayer.getCurrentPosition();
            //set seekbar progress
            seekbar.setProgress((int) timeElapsed);
            //set time remaing
            double timeRemaining = finalTime - timeElapsed;
            duration.setText(String.format("%d min, %d sec", TimeUnit.MILLISECONDS.toMinutes((long) timeRemaining), TimeUnit.MILLISECONDS.toSeconds((long) timeRemaining) - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes((long) timeRemaining))));

            //repeat yourself that again in 100 miliseconds
            durationHandler.postDelayed(this, 100);
        }
    };

    // pause mp3 song
    public void pause(View view) {
        mediaPlayer.pause();
    }

    // go forward at forwardTime seconds
    public void forward(View view) {
        //check if we can go forward at forwardTime seconds before song endes
        if ((timeElapsed + forwardTime) <= finalTime) {
            timeElapsed = timeElapsed + forwardTime;

            //seek to the exact second of the track
            mediaPlayer.seekTo((int) timeElapsed);
        }
    }

    // go backwards at backwardTime seconds
    public void rewind(View view) {
        //check if we can go back at backwardTime seconds after song starts
        if ((timeElapsed - backwardTime) > 0) {
            timeElapsed = timeElapsed - backwardTime;

            //seek to the exact second of the track
            mediaPlayer.seekTo((int) timeElapsed);
        }
    }

}

UPDATE!!!

Here is the error from the log:

03-14 19:20:10.413    1191-1284/system_process W/AudioTrack﹕ AUDIO_OUTPUT_FLAG_FAST denied by client
03-14 19:20:10.422    1191-1416/system_process I/ActivityManager﹕ START u0 {act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.javacodegeeks.androidmediaplayerexample/.AndroidMediaPlayerExample (has extras)} from uid 10008 on display 0
03-14 19:20:10.457    4043-4043/? E/libprocessgroup﹕ failed to make and chown /acct/uid_10065: Read-only file system
03-14 19:20:10.457    4043-4043/? W/Zygote﹕ createProcessGroup failed, kernel missing CONFIG_CGROUP_CPUACCT?
03-14 19:20:10.457    4043-4043/? I/art﹕ Not late-enabling -Xcheck:jni (already on)
03-14 19:20:10.461    1191-3310/system_process I/ActivityManager﹕ Start proc com.javacodegeeks.androidmediaplayerexample for activity com.javacodegeeks.androidmediaplayerexample/.AndroidMediaPlayerExample: pid=4043 uid=10065 gids={50065, 9997, 3003} abi=x86
03-14 19:20:10.493    4043-4050/? E/art﹕ Failed sending reply to debugger: Broken pipe
03-14 19:20:10.493    4043-4050/? I/art﹕ Debugger is no longer active
03-14 19:20:10.515    4043-4043/? D/AndroidRuntime﹕ Shutting down VM
03-14 19:20:10.515    4043-4043/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.javacodegeeks.androidmediaplayerexample, PID: 4043
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.javacodegeeks.androidmediaplayerexample/com.javacodegeeks.androidmediaplayerexample.AndroidMediaPlayerExample}: java.lang.ClassCastException: com.javacodegeeks.androidmediaplayerexample.AndroidMediaPlayerExample cannot be cast to android.widget.AdapterView$OnItemSelectedListener
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.ClassCastException: com.javacodegeeks.androidmediaplayerexample.AndroidMediaPlayerExample cannot be cast to android.widget.AdapterView$OnItemSelectedListener
            at com.javacodegeeks.androidmediaplayerexample.AndroidMediaPlayerExample.onCreate(AndroidMediaPlayerExample.java:42)
            at android.app.Activity.performCreate(Activity.java:5933)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

Thanks!!

Answer 1

You have not added listener on your spinner. Do it in this manner after your adapter is set

dropdown.setAdapter(adapter);
spinner.setOnItemSelectedListener(this);

Also you activity has to implement OnItemSelectedListener

public class AndroidMediaPlayerExample extends Activity  implements OnItemSelectedListener