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我试着做在Android Studio中的MP3播放器，我已经加载的所有歌曲我的手机在ArrayList中称为audioList，但我不能让recyclerView，任何人都可以找到错误？Recyclerview Android不工作
MainActivity.java
import android.Manifest;
import android.content.ComponentName;
import android.content.ContentResolver;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.database.Cursor;
import android.net.Uri;
import android.os.Build;
import android.os.IBinder;
import android.provider.MediaStore;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.widget.Toast;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
private MediaPlayerService player;
private boolean serviceBound = false;
private ArrayList<Audio> audioList;
private RWAdapter adapt;
RecyclerView recyclerView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.M){
requestPermissions(new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, 0);
}
RecyclerView rv = (RecyclerView) findViewById(R.id.myRecyclerView);
assert rv != null;
rv.setLayoutManager(new LinearLayoutManager(this));;
loadAudio();
RWAdapter rwa = new RWAdapter(audioList);
rv.setAdapter(rwa);
playAudio(audioList.get(22).getData());
}
//ulozi sa instancia
@Override
protected void onSaveInstanceState(Bundle outState) {
outState.putBoolean("ServiceState", serviceBound);
super.onSaveInstanceState(outState);
}
//obnovi sa instancia tam kde bola naposledy ulozena
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
serviceBound = savedInstanceState.getBoolean("ServiceState");
}
//znici instanciu
@Override
protected void onDestroy() {
super.onDestroy();
if(serviceBound){
unbindService(serviceConnection);
player.stopSelf();
}
}
//viaze tuto triedu s prehravacom, nastavi hodnotu serviceBound na true ked sa vytvori spojenie
private ServiceConnection serviceConnection = new ServiceConnection(){
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
MediaPlayerService.LocalBinder binder = (MediaPlayerService.LocalBinder) service;
player = binder.getService();
serviceBound = true;
Toast.makeText(MainActivity.this, "Service bound", Toast.LENGTH_SHORT).show();
}
@Override
public void onServiceDisconnected(ComponentName name) {
serviceBound = false;
}
};
//Metoda dava spravu,intnet druhej aktivite o spusteni hudby
private void playAudio(String media){
if(!serviceBound){
Intent playerIntent = new Intent(this,MediaPlayerService.class);
playerIntent.putExtra("media",media);
startService(playerIntent);
bindService(playerIntent, serviceConnection, Context.BIND_AUTO_CREATE);
} else {
}
}
//nacita pesnicky z mobilu
private void loadAudio() {
ContentResolver contentResolver = getContentResolver();
Uri uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
String selection = MediaStore.Audio.Media.IS_MUSIC + "!= 0";
String sortOrder = MediaStore.Audio.Media.TITLE + " ASC";
Cursor cursor = contentResolver.query(uri, null, selection, null, sortOrder);
if(cursor != null && cursor.getCount() > 0) {
audioList = new ArrayList<>();
while (cursor.moveToNext()){
String data = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.DATA));
String title = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.TITLE));
String album = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.ALBUM));
String artist = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.ARTIST));
audioList.add(new Audio(data, title, album, artist));
}
}
cursor.close();
}
}
RecyclerViewAdapter
package com.example.rsabo.mp3player;
import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import java.util.Collections;
import java.util.List;
/**
* Created by RSabo on 15-Apr-17.
*/
public class RWAdapter extends RecyclerView.Adapter<RWAdapter.MyViewHolder>{
private List<Audio> list;
private Context context;
public class MyViewHolder extends RecyclerView.ViewHolder {
TextView title;
ImageView play_pause;
MyViewHolder(View itemView) {
super(itemView);
title = (TextView) itemView.findViewById(R.id.title);
play_pause = (ImageView) itemView.findViewById(R.id.play_pause);
itemView.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
Audio currentAudio = list.get(getAdapterPosition());
}
});
}
}
public RWAdapter(List<Audio> list) {
this.list = list;
this.context = context;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
//Inflate the layout, initialize the View Holder
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_songov, parent, false);
return new MyViewHolder(v);
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
//Use the provided View Holder on the onCreateViewHolder method to populate the current row on the RecyclerView
holder.title.setText(list.get(position).getTitle());
}
@Override
public int getItemCount() {
//returns the number of elements the RecyclerView will display
return list.size();
}
}
activity_main.xml中
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
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.example.rsabo.mp3player.MainActivity">
<include layout="@layout/list_songov" />
list_songov.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="@+id/myRecyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
什么问题你面对？请解释 。 –
的主要问题是，即时得到这些错误显示java.lang.NullPointerException：在上一个com.example.rsabo空对象引用 尝试调用虚拟方法“无效android.widget.TextView.setText（java.lang.CharSequence中）” .mp3player.RWAdapter.onBindViewHolder（RWAdapter.java:59） at com.example.rsabo.mp3player.RWAdapter.onBindViewHolder（RWAdapter.java:19） –