Media Player導致應用程序崩潰

Question

我的測驗應用程序崩潰是什么時候期望聽到正確/錯誤答案的聲音。 這曾經工作過，現在卻行不通，我不明白為什么。 有人可以幫我嗎？ 編碼：

import java.util.List;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TextView;
import android.widget.Toast;
import com.example.vtorferreira.R;


public class QuizActivity extends Activity {

List<Question> quesList;
int score=0;
int qid=0;
Question currentQ;
TextView txtQuestion;
RadioButton rda, rdb, rdc;
Button butNext;

@Override

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_quiz);

   final MediaPlayer wrong_answer= MediaPlayer.create(this,   R.raw.wrong_answer);
   final MediaPlayer correct_answer= MediaPlayer.create(this, R.raw.correct_answer);


    DbHelper db=new DbHelper(this);

    quesList=db.getAllQuestions();
    currentQ=quesList.get(qid);
    txtQuestion=(TextView)findViewById(R.id.textView1);

    rda=(RadioButton)findViewById(R.id.radio0);
    rdb=(RadioButton)findViewById(R.id.radio1);
    rdc=(RadioButton)findViewById(R.id.radio2);

    butNext=(Button)findViewById(R.id.button1);
    setQuestionView();
    butNext.setOnClickListener(new View.OnClickListener() {
        @Override

        public void onClick(View v) {
            RadioGroup grp=(RadioGroup)findViewById(R.id.radioGroup1);
            RadioButton answer=(RadioButton)findViewById(grp.getCheckedRadioButtonId());

            if(currentQ.getANSWER().equals(answer.getText()))
            {
                correct_answer.start();
                score++;
                Toast.makeText(getApplicationContext(),"Correct!", Toast.LENGTH_SHORT).show();

            }else{
                wrong_answer.start();
                Toast.makeText(getApplicationContext(),"Wrong...", Toast.LENGTH_SHORT).show();
            }
            if(qid<9){
                currentQ=quesList.get(qid);
                setQuestionView();
            }else{
                Intent intent = new Intent(QuizActivity.this, ResultActivity.class);
                Bundle b = new Bundle();
                b.putInt("score", score); //Your score
                intent.putExtras(b); //Put your score to your next Intent
                startActivity(intent);
                finish();
            }
        }
    });
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_quiz, menu);
    return true;
}
private void setQuestionView()
{
    txtQuestion.setText(currentQ.getQUESTION());
    rda.setText(currentQ.getOPTA());
    rdb.setText(currentQ.getOPTB());
    rdc.setText(currentQ.getOPTC());
    qid++;
}
public void onBackPressed(){

 }
}

日志：java.lang.NullPointerException：嘗試在空對象引用上調用虛擬方法'void android.media.MediaPlayer.start（）'

提前致謝

Answer 1

您應該編寫correct_answer.prepare(); 在correct_answer.start();之前correct_answer.start();