应用程序在启动时关闭

Question

我正在尝试在android studio中制作音乐播放器，但是当我尝试在手机或AVD上测试我的应用程序时，它只会在屏幕上闪烁（一秒钟打开和关闭）。我是android studio的新手，如果您能给我一些提示，我会向您提出要求。

这是我的媒体光标适配器类：

package com.example.musicplayer;


import android.content.Context;
import android.database.Cursor;
import android.provider.MediaStore;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.SimpleCursorAdapter;
import android.widget.TextView;

import java.math.BigDecimal;



public class MediaCursorAdapter extends SimpleCursorAdapter {
public MediaCursorAdapter(Context context, int layout, Cursor c) {
    super(context, layout, c, new String[]{MediaStore.MediaColumns.DISPLAY_NAME,
                    MediaStore.MediaColumns.TITLE,MediaStore.Audio.AudioColumns.DURATION},
            new int[]{R.id.displayname, R.id.title, R.id.duration});
}

@Override
public void bindView(View view, Context context, Cursor cursor) {
    TextView title = (TextView) view.findViewById(R.id.title);
    TextView name = (TextView) view.findViewById(R.id.displayname);
    TextView duration = (TextView) view.findViewById(R.id.duration);

    name.setText(cursor.getString(cursor.getColumnIndex(
            MediaStore.MediaColumns.DISPLAY_NAME)));
    title.setText(cursor.getString(cursor.getColumnIndex(
            MediaStore.MediaColumns.TITLE)));
    long durationInMS = Long.parseLong(cursor.getString(
            cursor.getColumnIndex(MediaStore.Audio.AudioColumns.DURATION)));

    double durationInMin = ((double) durationInMS / 1000.0) / 60.0;
    durationInMin = new BigDecimal(Double.toString(durationInMin)).
            setScale(2, BigDecimal.ROUND_UP).doubleValue();
    duration.setText("" + durationInMin);
    view.setTag(cursor.getString(cursor.getColumnIndex(MediaStore.MediaColumns.DATA)));
}

@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
    LayoutInflater inflater = LayoutInflater.from(context);
    View v = inflater.inflate(R.layout.item, parent, false);
    bindView(v, context, cursor);
    return v;
    }
}

这是我的主要活动课：

package com.example.musicplayer;

import android.app.ListActivity;
import android.database.Cursor;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Handler;
import android.provider.MediaStore;
import android.util.Log;
import android.view.View;
import android.widget.ImageButton;
import android.widget.ListView;
import android.widget.SeekBar;
import android.widget.TextView;

import java.io.IOException;

public class MainActivity extends ListActivity {
private static final int UPDATE_FREQUENCY = 500;
private static final int STEP_VALUE = 4000;

private TextView selectedfile = null;
private SeekBar seekBar = null;
private MediaPlayer player = null;
private ImageButton prev = null;
private ImageButton play = null;
private ImageButton next = null;
private MediaCursorAdapter adapter = null;

private boolean isStarted = true;
private String currentFile = "";
private boolean isMovingSeekBar = false;
private final Handler handler = new Handler();

private final Runnable updatePositinRunnable = new Runnable() {
    @Override
    public void run() {
        updatePosition();
    }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    selectedfile = (TextView) findViewById(R.id.selecteditem);
    seekBar = (SeekBar) findViewById(R.id.seekBar);
    prev = (ImageButton) findViewById(R.id.previous);
    play = (ImageButton) findViewById(R.id.play);
    next = (ImageButton) findViewById(R.id.next);

    player = new MediaPlayer();
    player.setOnCompletionListener(onCompletion);
    player.setOnErrorListener(onError);
    seekBar.setOnSeekBarChangeListener(seekBarChanged);

    Cursor cursor = getContentResolver().query(MediaStore.Audio.Media.
            EXTERNAL_CONTENT_URI, null, null, null, null);

    if (null != cursor) {
        cursor.moveToFirst();
        adapter = new MediaCursorAdapter(this, R.layout.item, cursor);
        setListAdapter(adapter);
        prev.setOnClickListener(OnButtonClick);
        play.setOnClickListener(OnButtonClick);
        next.setOnClickListener(OnButtonClick);
    }
}

@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
    super.onListItemClick(l, v, position, id);
    currentFile = (String) v.getTag();
    startPlay(currentFile);
}

private void startPlay(String file) {
    Log.i("Selected: ", file);
    selectedfile.setText(file);
    seekBar.setProgress(0);
    player.stop();
    player.reset();

    try {
        player.setDataSource(file);
        player.prepare();
        player.start();
    } catch (IllegalArgumentException e) {
        e.printStackTrace();
    } catch (IllegalStateException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    seekBar.setMax(player.getDuration());
    play.setImageResource(android.R.drawable.ic_media_pause);
    updatePosition();
    isStarted = true;
}

private void stopPlay() {
    player.stop();
    player.reset();
    play.setImageResource(android.R.drawable.ic_media_play);
    handler.removeCallbacks(updatePositinRunnable);
    seekBar.setProgress(0);
    isStarted = false;
}

@Override
protected void onDestroy() {
    super.onDestroy();
    handler.removeCallbacks(updatePositinRunnable);
    player.stop();
    player.reset();
    player.release();
    player = null;
}

private void updatePosition() {
    handler.removeCallbacks(updatePositinRunnable);
    seekBar.setProgress(player.getCurrentPosition());
    handler.postDelayed(updatePositinRunnable, UPDATE_FREQUENCY);
}

private View.OnClickListener OnButtonClick = new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.play: {
                if (player.isPlaying()) {
                    handler.removeCallbacks(updatePositinRunnable);
                    player.pause();
                    play.setImageResource(android.R.drawable.ic_media_play);
                } else {
                    if (isStarted) {
                        player.start();
                        play.setImageResource(android.R.drawable.ic_media_pause);
                        updatePosition();
                    } else {
                        startPlay(currentFile);
                    }
                }
                break;
            }

            case R.id.next: {
                int seekto = player.getCurrentPosition() + STEP_VALUE;
                if (seekto > player.getDuration())
                    seekto = player.getDuration();
                player.pause();
                player.seekTo(seekto);
                player.start();
                break;
            }

            case R.id.previous: {
                int seekto = player.getCurrentPosition() - STEP_VALUE;
                if (seekto < 0)
                    seekto = 0;
                player.pause();
                player.seekTo(seekto);
                player.start();
                break;
            }
        }
    }
};
private MediaPlayer.OnCompletionListener onCompletion = new MediaPlayer.OnCompletionListener() {
    @Override
    public void onCompletion(MediaPlayer mp) {
        stopPlay();
    }

    ;
};
private MediaPlayer.OnErrorListener onError = new MediaPlayer.OnErrorListener() {
    @Override
    public boolean onError(MediaPlayer mp, int what, int extra) {
        return false;
    }
};

private SeekBar.OnSeekBarChangeListener seekBarChanged =
        new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                if (isMovingSeekBar) {
                    player.seekTo(progress);
                    Log.i("OnSeekBarChangeListener", "OnProgressChanged");
                }
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {
                isMovingSeekBar = true;
            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {
                isMovingSeekBar = false;
            }
        };

，这是事件日志： Event log

这是logcat：

2019-02-27 18：01：08.704 7280-7280 / com.example.musicplayer E / Android运行时：致命异常：主要     流程：com.example.musicplayer，PID：7280     java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.musicplayer / com.example.musicplayer.MainActivity}：java.lang.SecurityException：权限被拒绝：正在读取com.android.providers.media.MediaProvider uri内容：/ / media / external / audio / media from pid = 7280，uid = 10085需要android.permission.READ_EXTERNAL_STORAGE或grantUriPermission（）         在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2913）         在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3048）         在android.app.servertransaction.LaunchActivityItem.execute（LaunchActivityItem.java:78）         在android.app.servertransaction.TransactionExecutor.executeCallbacks（TransactionExecutor.java:108）         在android.app.servertransaction.TransactionExecutor.execute（TransactionExecutor.java:68）         在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1808）         在android.os.Handler.dispatchMessage（Handler.java:106）         在android.os.Looper.loop（Looper.java:193）         在android.app.ActivityThread.main（ActivityThread.java:6669）         在java.lang.reflect.Method.invoke（本机方法）         在com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run（RuntimeInit.java:493）         在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:858）      引起原因：java.lang.SecurityException：权限被拒绝：从pid = 7280中读取com.android.providers.media.MediaProvider uri content：// media / external / audio / media，uid = 10085需要android.permission.READ_EXTERNAL_STORAGE，或者grantUriPermission（）         在android.os.Parcel.createException（Parcel.java:1942）         在android.os.Parcel.readException（Parcel.java:1910）         在android.database.DatabaseUtils.readExceptionFromParcel（DatabaseUtils.java:183）         在android.database.DatabaseUtils.readExceptionFromParcel（DatabaseUtils.java:135）         在android.content.ContentProviderProxy.query（ContentProviderNative.java:418）         在android.content.ContentResolver.query（ContentResolver.java:802）         在android.content.ContentResolver.query（ContentResolver.java:752）         在android.content.ContentResolver.query（ContentResolver.java:710）         在com.example.musicplayer.MainActivity.onCreate（MainActivity.java:58）         在android.app.Activity.performCreate（Activity.java:7136）         在android.app.Activity.performCreate（Activity.java:7127）         在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1271）         在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2893）         在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3048）         在android.app.servertransaction.LaunchActivityItem.execute（LaunchActivityItem.java:78）         在android.app.servertransaction.TransactionExecutor.executeCallbacks（TransactionExecutor.java:108）         在android.app.servertransaction.TransactionExecutor.execute（TransactionExecutor.java:68）         在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1808）         在android.os.Handler.dispatchMessage（Handler.java:106）         在android.os.Looper.loop（Looper.java:193）         在android.app.ActivityThread.main（ActivityThread.java:6669）         在java.lang.reflect.Method.invoke（本机方法）         在com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run（RuntimeInit.java:493）         在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:858） 2019-02-27 18：01：08.787 7280-7280 / com.example.musicplayer I /进程：正在发送信号。 PID：7280 SIG：9