你好，我是一名Java编程（Android）的新手。目前我正在学习在片段中使用RecyclerView和Volley，并需要帮助。为什么当从片段1切换到片段2，然后再返回片段1时，RecyclerView会消失？即使一开始RecyclerView是可用的？谢谢帮助。
这是BackgroundTask.java文件：
Context mContext;
ArrayList<List> mArrayList = new ArrayList<>();
String json_url = "http://192.168.43.215/belajar/contact_mad.php";
private static final String TAG = "BackgroundTask";
public BackgroundTask(Context context) {
this.mContext = context;
}
public ArrayList<List> getList()
{
JsonArrayRequest jsonArrayRequest = new JsonArrayRequest(Request.Method.POST, json_url, (String) null,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
int count = 0;
while (count<response.length())
{
try {
JSONObject jsonObject = response.getJSONObject(count);
List list = new List(jsonObject.getString("Id"),jsonObject.getString("ImageUrl"),jsonObject.getString("Name"));
mArrayList.add(list);
count++;
} catch (JSONException e) {
e.printStackTrace();
}
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(mContext,"Errorr.............",Toast.LENGTH_SHORT).show();
error.printStackTrace();
}
}
);
MySingleton.getInstance(mContext).addToRequestQue(jsonArrayRequest);
Log.e(TAG, "Log Dari background");
return mArrayList;
}
这是RecyclerAdapter.java文件。
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.MyViewHolder> {
ArrayList<List> mArrayList = new ArrayList<>();
private static final String TAG = "RecyclerAdapter";
public RecyclerAdapter(ArrayList<List> arrayList){
this.mArrayList = arrayList;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.row_item,parent,false);
MyViewHolder myViewHolder = new MyViewHolder(view);
return myViewHolder;
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
final String name = mTxtName.getText().toString();
final String email = mTxtEmail.getText().toString();
final String nameFood = this.mArrayList.get(position).getName();
final String imageUrl = this.mArrayList.get(position).getImageUrl();
holder.Name.setText(mArrayList.get(position).getName());
final Context context = holder.mImageView.getContext();
Picasso.with(context).load(mArrayList.get(position).getImageUrl()).into(holder.mImageView);
Log.e(TAG, "Log Dari On BindView");
holder.cvMain.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
/*Intent intent = new Intent(v.getContext(),ActivityClick.class);
Bundle bundle = new Bundle();
bundle.putString("imageUrl",imageUrl);
bundle.putString("name",name);
intent.putExtras(bundle);
v.getContext().startActivity(intent);*/
Toast.makeText(context, name, Toast.LENGTH_LONG).show();
}
});
}
@Override
public int getItemCount() {
return mArrayList.size();
}
public static class MyViewHolder extends RecyclerView.ViewHolder{
TextView Name;
RelativeLayout cvMain;
ImageView mImageView;
public MyViewHolder(View itemView) {
super(itemView);
mImageView = (ImageView) itemView.findViewById(R.id.imageView);
Name = (TextView)itemView.findViewById(R.id.txtName);
cvMain = (RelativeLayout) itemView.findViewById(R.id.cvMain);
}
}
这是MainMenu.java。
public class MainMenu extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
public static TextView mTxtName, mTxtEmail;
private Fragment fragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_menu);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
mTxtName = (TextView)navigationView.getHeaderView(0).findViewById(R.id.txtNavName);
mTxtEmail = (TextView)navigationView.getHeaderView(0).findViewById(R.id.txtNavEmail);
Bundle bundle = getIntent().getExtras();
mTxtName.setText(bundle.getString("name"));
mTxtEmail.setText(bundle.getString("email"));
android.support.v4.app.FragmentManager fm = getSupportFragmentManager();
android.support.v4.app.FragmentTransaction transaction = fm.beginTransaction();
transaction.replace(R.id.tempatfragment, new ListMakanan()).addToBackStack(null).commit();
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.cara_pesan) {
return true;
}else if(id == R.id.keluar){
finish();
return true;
}
return super.onOptionsItemSelected(item);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
android.support.v4.app.FragmentManager fm = getSupportFragmentManager();
android.support.v4.app.FragmentTransaction transaction = fm.beginTransaction();
if (id == R.id.list_makanan) {
transaction.replace(R.id.tempatfragment, new ListMakanan()).addToBackStack(null).commit();
} else if (id == R.id.pesan_makanan) {
transaction.replace(R.id.tempatfragment, new PesanMakanan()).addToBackStack(null).commit();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
这是ListMakanan.java的片段。
public class ListMakanan extends Fragment {
RecyclerView mRecyclerView;
RecyclerView.Adapter mAdapter;
RecyclerView.LayoutManager mLayoutManager;
ArrayList<List> mArrayList = new ArrayList<>();
private static final String TAG = "ListMakanan";
public ListMakanan() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_list__makanan, container, false);
}
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
mRecyclerView = (RecyclerView)view.findViewById(R.id.recyclervView);
mLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(mLayoutManager);
mRecyclerView.setHasFixedSize(true);
BackgroundTask backgroundTask = new BackgroundTask(getActivity());
mArrayList = backgroundTask.getList();
mAdapter = new RecyclerAdapter(mArrayList);
mRecyclerView.setAdapter(mAdapter);
Log.e(TAG, "Log Dari View Created");
}
transaction.add(R.id.tempatfragment, new ListMakanan()).addToBackStack(null).commit();- hanhanhanhan