java - 尝试调用虚方法 [空对象引用]
问题描述
我在过去的 5 天里试图解决这个问题。我真的不知道如何解决它。我得到Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
。检查我的代码:
RecyclerView.java
package etes.xdda.music;
import android.app.Dialog;
import android.content.Context;
import android.content.Intent;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.media.MediaPlayer;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
import java.util.List;
public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.MyViewHolder> implements View.OnClickListener{
Context mContext;
List<mList> mData;
Dialog myDialog;
private MediaPlayer mediaPlayer;
private int playbackPosition=0;
private LinearLayout menu_dialog;
public RecyclerViewAdapter(Context mContext, List<mList> mData) {
this.mContext = mContext;
this.mData = mData;
}
public void onClick(View view) {
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v;
v = LayoutInflater.from(mContext).inflate(R.layout.item_list, parent, false);
final MyViewHolder vHolder = new MyViewHolder(v);
// Dialog ini
myDialog = new Dialog(mContext);
myDialog.setContentView(R.layout.dialog);
myDialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
vHolder.item_play.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v)
{
TextView dialog_name_tv = (TextView) myDialog.findViewById(R.id.dialog_name_id);
TextView dialog_phone_tv = (TextView) myDialog.findViewById(R.id.dialog_author_id);
ImageView dialog_contact_img = (ImageView) myDialog.findViewById(R.id.dialog_img);
dialog_name_tv.setText(mData.get(vHolder.getAdapterPosition()).getName());
dialog_phone_tv.setText(mData.get(vHolder.getAdapterPosition()).getPhone());
dialog_contact_img.setImageResource(mData.get(vHolder.getAdapterPosition()).getPhoto());
//Toast.makeText(mContext, "Test click "+String.valueOf(vHolder.getAdapterPosition()), Toast.LENGTH_SHORT).show();
myDialog.show();
}
});
vHolder.menu_play.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v)
{
menu_dialog = v.getRootView().findViewById(R.id.menu_dialog);
menu_dialog.setVisibility(v.VISIBLE);
MainActivity a = new MainActivity();
a.initAudio(v.getContext(), mData.get(vHolder.getAdapterPosition()).getURL());
MainActivity.setMargins(v.getRootView().findViewById(R.id.viewpager_id), 0,0,0,100);
}
});
return vHolder;
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
holder.tv_name.setText(mData.get(position).getName());
holder.tv_author.setText(mData.get(position).getPhone());
holder.img.setImageResource(mData.get(position).getPhoto());
}
@Override
public int getItemCount() {
return mData.size();
}
public static class MyViewHolder extends RecyclerView.ViewHolder {
private ImageButton item_play;
private LinearLayout menu_play;
private TextView tv_name;
private TextView tv_author;
private TextView tv_url;
private ImageView img;
public MyViewHolder(View itemView) {
super(itemView);
item_play = itemView.findViewById(R.id.info_id);
menu_play = itemView.findViewById(R.id.list_item_id);
tv_name = (TextView) itemView.findViewById(R.id.name_list);
tv_author = (TextView) itemView.findViewById(R.id.author_list);
img = (ImageView) itemView.findViewById(R.id.img_contact);
}
}
}
请注意,我在这部分调用MainActivity.java :
vHolder.menu_play.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v)
{
menu_dialog = v.getRootView().findViewById(R.id.menu_dialog);
menu_dialog.setVisibility(v.VISIBLE);
MainActivity a = new MainActivity();
a.initAudio(v.getContext(), mData.get(vHolder.getAdapterPosition()).getURL());
MainActivity.setMargins(v.getRootView().findViewById(R.id.viewpager_id), 0,0,0,100);
}
});
这是我的MainActivity.java
package etes.xdda.music;
import android.annotation.SuppressLint;
import android.content.Context;
import android.media.MediaPlayer;
import android.net.Uri;
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.LinearLayout;
public class MainActivity extends AppCompatActivity {
private DrawerLayout nDrawerLayout;
private ActionBarDrawerToggle mToggle;
private TabLayout tabLayout;
private ViewPager viewPager;
private viewPagerAdapter adapter;
public LinearLayout menu_dialog;
private String player_status = "playing";
private ImageButton player_img;
private static MediaPlayer mediaPlayer;
@SuppressLint("RestrictedApi")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
nDrawerLayout = findViewById(R.id.drawer);
menu_dialog = findViewById(R.id.menu_dialog);
menu_dialog.setVisibility(View.GONE);
player_img = findViewById(R.id.playorpause);
player_img.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//setMargins(viewPager, 0,0,0,110);
if (player_status == "playing") {
player_img.setImageResource(R.drawable.ic_play_arrow_black_24dp);
meplayer.pauseAudio();
player_status = "paused";
} else {
player_img.setImageResource(R.drawable.ic_pause_black_24dp);
meplayer.startAudio();
player_status = "playing";
}
}
});
//menu_dialog.setLayoutParams(new LinearLayout.LayoutParams(0, 0));
mToggle = new ActionBarDrawerToggle(this, nDrawerLayout, R.string.open, R.string.close);
nDrawerLayout.addDrawerListener(mToggle);
getSupportActionBar().setDefaultDisplayHomeAsUpEnabled(true);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
tabLayout = findViewById(R.id.tablayout_id);
viewPager = findViewById(R.id.viewpager_id);
//viewPager.setLayoutParams(new ViewPager.LayoutParams(0, 0));
//setMarginBottom(viewPager, 0);
setMargins(viewPager, 0,0,0,0);
adapter = new viewPagerAdapter(getSupportFragmentManager());
//Add fragments here
adapter.addFragment(new fragmentList(), ""); //Lista de música
adapter.addFragment(new fragmentFrequent(), ""); //Frequentes
adapter.addFragment(new fragmentPlayList(), ""); //Playlist
viewPager.setAdapter(adapter);
tabLayout.setupWithViewPager(viewPager);
tabLayout.getTabAt(0).setIcon(R.drawable.ic_music_note_black_24dp); //Lista de música
tabLayout.getTabAt(1).setIcon(R.drawable.ic_filter_list_black_24dp); // Frequentes
tabLayout.getTabAt(2).setIcon(R.drawable.ic_queue_music_black_24dp); // Playlist
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
if (mToggle.onOptionsItemSelected(item)) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
// Sync the toggle state after onRestoreInstanceState has occurred.
mToggle.syncState();
}
public static void setMargins (View v, int l, int t, int r, int b) {
if (v.getLayoutParams() instanceof ViewGroup.MarginLayoutParams) {
ViewGroup.MarginLayoutParams p = (ViewGroup.MarginLayoutParams) v.getLayoutParams();
p.setMargins(l, t, r, b);
v.requestLayout();
}
}
public void initAudio(final Context context, final String url) {
if (mediaPlayer == null) {
mediaPlayer = MediaPlayer.create(context, Uri.parse(url));
}
mediaPlayer.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
@Override
public void onCompletion(MediaPlayer mp) {
//Toast.makeText(context, "TEST", Toast.LENGTH_LONG).show();
killMediaPlayer();
updateLayout();
}
});
mediaPlayer.start();
}
private static void killMediaPlayer() {
if (mediaPlayer != null) {
try {
mediaPlayer.reset();
mediaPlayer.release();
mediaPlayer = null;
} catch (Exception e) {
e.printStackTrace();
}
}
}
private void updateLayout() {
try {
menu_dialog = findViewById(R.id.menu_dialog);
menu_dialog.setVisibility(View.GONE);
} catch (Exception e) {
e.printStackTrace();
}
}
导致崩溃的代码部分是这样的:
private void updateLayout() {
try {
menu_dialog = findViewById(R.id.menu_dialog);
menu_dialog.setVisibility(View.GONE);
} catch (Exception e) {
e.printStackTrace();
}
}
@edit:我已经添加了这段代码,我不知道是否有帮助
片段列表.java
package etes.xdda.music;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonArrayRequest;
import com.android.volley.toolbox.Volley;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;
public class fragmentList extends Fragment {
View v;
private RecyclerView myrecyclerview;
private List<mList> lstContact;
private String URL_JSON = "https://pastebin.com/raw/fG3zd40U";
private JsonArrayRequest ArrayRequest;
private RequestQueue requestQueue ;
MainActivity activity;
public fragmentList() {
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
v = inflater.inflate(R.layout.list_fragment,container,false);
myrecyclerview = (RecyclerView) v.findViewById(R.id.list_recyclerview);
RecyclerViewAdapter recyclerViewAdapter = new RecyclerViewAdapter(activity, lstContact);
myrecyclerview.setLayoutManager(new LinearLayoutManager(getActivity()));
myrecyclerview.setAdapter(recyclerViewAdapter);
return v;
}
@Override
public void onCreate(@Nullable Bundle savedInstaceState) {
super.onCreate(savedInstaceState);
_JSONcall();
}
public void _JSONcall() {
lstContact = new ArrayList<>();
ArrayRequest = new JsonArrayRequest(URL_JSON, new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
JSONObject jsonObject = null;
for (int i = 0 ; i<response.length();i++) {
try {
jsonObject = response.getJSONObject(i);
lstContact.add(new mList(jsonObject.getString("name"), jsonObject.getString("description"), jsonObject.getString("link"), R.drawable.ic_play_circle_filled_black_24dp));
}
catch (JSONException e) {
e.printStackTrace();
Toast.makeText(getActivity(), "Error 1!",
Toast.LENGTH_LONG).show();
}
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(getActivity(), "Error 3!",
Toast.LENGTH_LONG).show();
}
});
requestQueue = Volley.newRequestQueue(getActivity().getApplicationContext());
requestQueue.add(ArrayRequest);
}
}
请帮帮我,我对我应该做什么没有更多的想法。谢谢
解决方案
看看你的代码,看起来你做错了很多事情。比如这条线
MainActivity a = new MainActivity();
您不能以这种方式实例化服务、活动、片段等生命周期组件。当您调用启动方法等时,Android 会为您提供这些组件。由于上述行创建的活动不会经历通过使用 startActivity 启动的活动的生命周期调用。结果,活动的 setContentView 永远不会被调用,并且您会收到此错误。您必须删除此行并正确实施,错误就会消失。
还要补充一点,当您需要调用已启动的旧实例上的方法时,您实际上是在创建一个新的活动实例。
编辑:试试这样。
MainActivity activity;
List<mList> mData;
Dialog myDialog;
private MediaPlayer mediaPlayer;
private int playbackPosition=0;
private LinearLayout menu_dialog;
public RecyclerViewAdapter(MainActivity activity, List<mList> mData) {
this.activity = activity;
this.mData = mData;
}
接着
vHolder.menu_play.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v)
{
menu_dialog = v.getRootView().findViewById(R.id.menu_dialog);
menu_dialog.setVisibility(v.VISIBLE);
activity.initAudio(v.getContext(), mData.get(vHolder.getAdapterPosition()).getURL());
activity.setMargins(v.getRootView().findViewById(R.id.viewpager_id), 0,0,0,100);
}
});
还从主要活动功能中删除静态
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