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當按下另一個活動的排序按鈕時，Android 中的 RecyclerView 變為空白

[英]RecyclerView in Android goes blank when pressing sort button from another activity

 原文  2019-10-04 04:38:14  8   3    java/ android/ android-recyclerview/ adapter

問題描述

好的，所以我正在嘗試對從 XML 開始初始化的 recyclerView 進行排序。 我可以在啟動應用程序時看到電子郵件，也可以單擊它們。 排序按鈕位於設置活動中，但是每當我回到我的 RecyclerView 所在的主要活動時，單擊按鈕后，我的 recyclerView 就會變為空白。

這是我的 MainActivity

package com.example.assignment_1;

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";

    //Variables
    private ArrayList<String> mNames = new ArrayList<>();
    private ArrayList<String> mImageurls = new ArrayList<>();
    private ArrayList<String> mHeaders = new ArrayList<>();
    private ArrayList<String> mContent = new ArrayList<>();
    static ArrayList<AssignmentEmail> emails = new ArrayList<>();
    private RecyclerViewAdapdter adapter;
    private RecyclerView recyclerView;
    private Context mContext;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        EmailProvider emailProvider = new EmailProvider();
        Context context = getApplicationContext();
        if(emails.isEmpty() == true){
            emails = emailProvider.getEmails(context);
            loadEmails();
        }
    }

    private void loadEmails(){
        Log.d(TAG, "loadEmails: initBitmaps Called");
        for(int i = 0; i < emails.size(); i++) {
            mImageurls.add("@drawable/e1.jpg");
            mNames.add(emails.get(i).getAuthor());
            mHeaders.add(emails.get(i).getTitle());
            mContent.add(emails.get(i).getBody());
        }
        initRecyclerView();
    }

    public static ArrayList<AssignmentEmail> getEmails(){
        return emails;
    }

    public void sortEmails(ArrayList<AssignmentEmail> arrayOfEmails){
        Comparator<AssignmentEmail> compareByAuthor = (AssignmentEmail o1, AssignmentEmail o2) -> o1.getAuthor().compareTo( o2.getAuthor());
        Collections.sort(arrayOfEmails, compareByAuthor);
        mImageurls.clear();
        mNames.clear();
        mHeaders.clear();
        mContent.clear();
        for(int i = 0; i < arrayOfEmails.size(); i++) {
            mImageurls.add("@drawable/e1.jpg");
            mNames.add(arrayOfEmails.get(i).getAuthor());
            mHeaders.add(arrayOfEmails.get(i).getTitle());
            mContent.add(arrayOfEmails.get(i).getBody());
        }
        adapter = new RecyclerViewAdapdter(mImageurls,mNames,mHeaders,mContent,this);
        adapter.notifyDataSetChanged();
    }

    private void initRecyclerView(){
        Log.d(TAG, "initRecyclerView: init RecyclerView");
        recyclerView  = findViewById(R.id.recyclerview);
        adapter = new RecyclerViewAdapdter(mImageurls,mNames,mHeaders,mContent,this);
        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate activity menu items.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item){
        int id = item.getItemId();

        if (id == R.id.action_settings){
            Intent intent = new Intent(getApplicationContext(), Settings.class);
            startActivity(intent);
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

這是我的 RecyclerViewAdapter

package com.example.assignment_1;
import android.content.Context;
import android.content.Intent;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.RelativeLayout;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.bumptech.glide.Glide;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

import de.hdodenhof.circleimageview.CircleImageView;

public class RecyclerViewAdapdter extends RecyclerView.Adapter<RecyclerViewAdapdter.ViewHolder>  {

    private static final String TAG = "RecyclerViewAdapter";
    private ArrayList<String> mImages = new ArrayList<>();
    private ArrayList<String> mEmailTitle = new ArrayList<>();
    private ArrayList<String> mEmailHeader = new ArrayList<>();
    private ArrayList<String> mEmailContent = new ArrayList<>();
    private Context mContext;

    public RecyclerViewAdapdter(ArrayList<String> mImages, ArrayList<String> mEmailTitle, ArrayList<String> mEmailHeader, ArrayList<String> mEmailContent, Context mContext) {
        this.mImages = mImages;
        this.mEmailTitle = mEmailTitle;
        this.mEmailHeader = mEmailHeader;
        this.mEmailContent = mEmailContent;
        this.mContext = mContext;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_layout, parent, false);
        ViewHolder holder = new ViewHolder(view);
        return holder;
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, final int position) {
        Log.d(TAG, "onBindViewHolder: Called");

        Glide.with(mContext)
                .asBitmap()
                .load(mImages.get(position))
                .into(holder.Image);

        holder.email_from.setText(mEmailTitle.get(position));
        holder.email_header.setText(mEmailHeader.get(position));
        holder.email_contents.setText(mEmailContent.get(position));
        holder.Email_interface.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //Log.d(TAG, "onClick: Email Clicked");
                //Toast.makeText(mContext, mEmailTitle.get(position),Toast.LENGTH_SHORT).show();
                Intent intent = new Intent(mContext.getApplicationContext(), LayoutItemsActivity.class);
                intent.putExtra("EmailFrom",mEmailTitle.get(position));
                intent.putExtra("EmailHeader",mEmailHeader.get(position));
                intent.putExtra(("EmailContents"),mEmailContent.get(position));
                mContext.startActivity(intent);
            }
        });
    }

    @Override
    public int getItemCount() {
        return mEmailTitle.size();
    }


    public class ViewHolder extends RecyclerView.ViewHolder{

        CircleImageView Image;
        TextView email_from;
        TextView email_header;
        TextView email_contents;
        RelativeLayout Email_interface;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            Image = itemView.findViewById(R.id.image);
            email_from = itemView.findViewById(R.id.EmailFrom);
            email_header = itemView.findViewById(R.id.EmailHeader);
            email_contents = itemView.findViewById(R.id.EmailContents);
            Email_interface = itemView.findViewById(R.id.email_interface);
        }
    }
}

這是我的按鈕所在的位置


package com.example.assignment_1;

import android.content.Intent;
import android.os.Bundle;

import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;

import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

import android.view.View;
import android.widget.Button;

import java.util.ArrayList;

public class Settings extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_settings);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        Button resetButton = findViewById(R.id.button2);
        resetButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                MainActivity mainActivity = new MainActivity();
                ArrayList<AssignmentEmail> emailArray = mainActivity.getEmails();
                mainActivity.sortEmails(emailArray);
            }
        });
    }

}

3 個解決方案

解決方案1
 1  2019-10-04 04:54:10

如果您仍想通過設置活動刷新回收站視圖，請使用此庫。

https://github.com/greenrobot/EventBus

實施鏈接

https://stackoverflow.com/a/40987755/6452937

您無法在您提到的活動之間進行交流。

解決方案2
 1  2019-10-04 05:17:59

從您的MainActivity使用startActivityForResult()方法調用Settings

例如：

    if (id == R.id.action_settings){
        Intent intent = new Intent(getApplicationContext(), Settings.class);
        startActivityForResult(intent,1);
        return true;
    }

在您的Settings Activity中設置您想要返回MainActivity的數據。 如果您不想返回，請不要設置任何內容。

resetButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent returnIntent = new Intent();
                setResult(Activity.RESULT_OK,returnIntent);
                finish();
            }
        });

現在在您的main activity中，您必須為onActivityResult()方法編寫以下代碼。

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {

    if (requestCode == 1) {
        if(resultCode == Activity.RESULT_OK){
            // here you can sorting your recyclerview
            sortEmails(getEmails());
        }
        if (resultCode == Activity.RESULT_CANCELED) {
            //Write your code if there's no result
        }
    }
}

另一種方式

如果您不想在單擊resetbutton按鈕后終止setting activity ，則可以使用shared preference 。

例子

public class SharedPrefManager{
  private static SessionManager jInstance;
  private final SharedPreferences prefs;
  private final SharedPreferences.Editor editor;

  // private constructor to force use of 
  // getInstance() to create Singleton object 
  private SharedPrefManager(Context context) {
      prefs = context.getSharedPreferences("Your_Preference_name", Context.MODE_PRIVATE);
      editor = prefs.edit();
  }

  // create the instance when it is accessed for the first time
  public static synchronized SharedPrefManager getInstance(Context context) {
      if (jInstance != null) {
          return jInstance;
      } else {
          jInstance = new SharedPrefManager(context);
          return jInstance;
      }
  }

  
  public void isSortedByEmail(boolean emailSorting){
      editor.putString("emailSorting",emailSorting);
      editor.apply();
  }

 
  public boolean isSortedByEmail(){
      return prefs.getBoolean("emailSorting",false);
  }
}

在您的setting activity中，您必須執行以下操作

resetButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
      SharedPrefManager.getInstance(context).isSortedByEmail(true);
    }
});

在onStart()中的main activity中

@Override
protected void onStart(){
   super.onStart();
   if(SharedPrefManager.getInstance(context).isSortedByEmail()){
     // here you can sorting your recyclerview
     sortEmails(getEmails());
   }
}

解決方案3
 0  2019-10-04 06:19:41

您在設置中初始化了MainActivity ，但該引用與您正在顯示的實際MainActivity不同。 我在適配器中發現了一些與數據集相關的其他問題，需要改進。 之后，您需要找到一種將過濾器信息從Settings發送到MainActivity的方法。 有幾種方法，但我建議您在您的情況下使用 SharedPreference 。

在Settings中，您應該將過濾器設置放入SharedPreference並在MainActivity中獲取它們的值

public class Settings extends AppCompatActivity {

    SharedPreferences.Editor editSettings;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...
        editSettings = getSharedPreferences("filter", Context.MODE_PRIVATE).edit();
        resetButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editSettings.putBoolean("reset", true).apply();
            }
        });
    }
}

在Adapter中進行以下更改，

public class RecyclerViewAdapdter extends RecyclerView.Adapter<RecyclerViewAdapdter.ViewHolder>  {

    private static final String TAG = "RecyclerViewAdapter";
    private ArrayList<String> mImages = new ArrayList<>();
    private ArrayList<String> mEmailTitle = new ArrayList<>();
    private ArrayList<String> mEmailHeader = new ArrayList<>();
    private ArrayList<String> mEmailContent = new ArrayList<>();
    private Context mContext;

    public RecyclerViewAdapdter(Context mContext) {
        this.mContext = mContext;
    }

    public void submitData((ArrayList<String> mImages, ArrayList<String> mEmailTitle, ArrayList<String> mEmailHeader, ArrayList<String> mEmailContent) {
        this.mImages.clear();
        this.mEmailTitle.clear();
        this.mEmailHeader.clear();
        this.mEmailContent.clear();

        this.mImages.addAll(mImages);
        this.mEmailTitle.addAll(mEmailTitle);
        this.mEmailHeader.addAll(mEmailHeader);
        this.mEmailContent.addAll(mEmailContent);

        notifyDataSetChanged()
    }

    ...
}

當 SharedPreference 中的值為 true 時，在MainActivity中覆蓋onResume()並更新列表，

public class MainActivity extends AppCompatActivity {

    ...

    SharedPreferences spSettings;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        spSettings = getSharedPreferences("filter", Context.MODE_PRIVATE);

        ...
    }

    @Override
    protected void onResume() {
        super.onResume();
        boolean reset = spSettings.getBoolean("reset", false);
        if(reset) {
            ArrayList<AssignmentEmail> emailArray = getEmails();
            sortEmails(emailArray);
        }
    }

    private void initRecyclerView(){
        ...

        adapter = new RecyclerViewAdapdter(mContent,this);
        adapter.submitData(mImageurls,mNames,mHeaders);

        ...
    }

    public void sortEmails(ArrayList<AssignmentEmail> arrayOfEmails){
        ...

        adapter.submitData(mImageurls,mNames,mHeaders,mContent);
    }

}

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