RecycleView不会更新

Question

我仍然是Java和android的新手

我的问题是，如果关闭应用程序并再次运行，recycleview只会得到更新并添加新添加的标记。如何让应用程序立即更新循环视图，以显示新的标签。

java代码

package com.deitel.favoritesites;

import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.Bundle;
import android.preference.DialogPreference;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.TextInputLayout;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.View.OnLongClickListener;
import android.view.inputmethod.InputMethodManager;
import android.widget.Adapter;
import android.widget.EditText;
import android.widget.TextView;

import android.view.Menu;
import android.view.MenuItem;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class MainActivity extends AppCompatActivity {
private static final String SITES="Sites";

private EditText urlEditText; //where user enters the URL
private EditText tagEditText;
private FloatingActionButton saveFloatingActionButton;
private SharedPreferences savedSites;
private List<String> tags;
private SitesAdapter adapter;

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

    urlEditText = ((TextInputLayout) findViewById(
            R.id.URLTextInputLayout)).getEditText();

    urlEditText.addTextChangedListener(textWatcher);
    tagEditText=((TextInputLayout)findViewById(R.id.tagTextInputLayout)).getEditText();
    tagEditText.addTextChangedListener(textWatcher);


    //get the shared prefrences containing the user saved URLs
    savedSites = getSharedPreferences(SITES, MODE_PRIVATE);

    //get the shared tags in an ArrayList then sort them
    tags = new ArrayList<>(savedSites.getAll().keySet());
    Collections.sort(tags, String.CASE_INSENSITIVE_ORDER);

    //get reference to the recycle to configure it
    RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);

    //use a linerlayout to display items in  a vertical list
    recyclerView.setLayoutManager(new LinearLayoutManager(this));

    //create recyclerView.Adopter to bind tags to the RecyclerView
    adapter = new SitesAdapter(tags, itemClickListener, itemLongClickListener);
    recyclerView.setAdapter(adapter);

    recyclerView.addItemDecoration(new ItemDivider(this));

    //register listner to save a new or edit search
    saveFloatingActionButton = (FloatingActionButton) findViewById(R.id.fab);
    saveFloatingActionButton.setOnClickListener(saveButtonListener);
    updateSaveFAB();
}
private final TextWatcher textWatcher= new TextWatcher() {
    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
        updateSaveFAB();
    }

    @Override
    public void afterTextChanged(Editable s) {
    }
};
//show or hide the saveFloatingActionButton
private void updateSaveFAB() {
    //check if there is input in both EditButton
    if (urlEditText.getText().toString().isEmpty() || tagEditText.getText().toString().isEmpty())
        saveFloatingActionButton.hide();
    else
        saveFloatingActionButton.show();
}
//saveButtonListener save a tag query pair into sharedPrefrece
private final OnClickListener saveButtonListener=new OnClickListener() {
    @Override
    public void onClick(View view) {
        String query = urlEditText.getText().toString();
        String tag = tagEditText.getText().toString();
        if (!query.isEmpty() && !tag.isEmpty()) {
            //hide the virtual keyboard
            ((InputMethodManager) getSystemService(
                    Context.INPUT_METHOD_SERVICE)).hideSoftInputFromWindow(view.getWindowToken(),0);
            addTaggedSites(tag, query);//add/update the search
            urlEditText.setText("");//Clear queryEditText
            tagEditText.setText("");//clear tagEditText
            urlEditText.requestFocus();
        }
    }
};
//add new search to file then refresh all button
private void addTaggedSites(String tag, String query) {
    //get a sharedprefrence editor to store new tag/query pair
    SharedPreferences.Editor preferencesEditor = savedSites.edit();
    preferencesEditor.putString(tag, query);
    preferencesEditor.apply();

    //if tag is new> add and sort tags then display update
    if (!tag.contains(tag)) {
        tags.add(tag);
        Collections.sort(tags, String.CASE_INSENSITIVE_ORDER);
        adapter.notifyDataSetChanged();
    }
}
//itemClickListener launches web broswer to display search results
private final OnClickListener itemClickListener=new OnClickListener() {
    @Override
    public void onClick(View view) {
        //get query string and create a URL represeting the search
        String tag= ((TextView) view).getText().toString();
        String urlString=getString(R.string.search_URL)+Uri.encode(savedSites.getString(tag,""),"UTF-8");

        //create an intent to lanuch a web broswer

        Intent webIntent= new Intent(Intent.ACTION_VIEW,Uri.parse(urlString));
        startActivity(webIntent);
    }
};
//itemLongClickListener displays a dialog allowing the user to share edit or delete a saved search
private final OnLongClickListener itemLongClickListener= new OnLongClickListener() {
    @Override
    public boolean onLongClick(View view) {
        //get the tag that the user long touched
        final String tag = ((TextView) view).getText().toString();

        //creatw a new AlertDialog
        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);

        //set the alertDialog title
        builder.setTitle(getString(R.string.share_edit_delete_title, tag));

        //set list of items to display and create event handler
        builder.setItems(R.array.dialog_items, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        switch (which) {
                            case 0://share
                                shareSites(tag);
                                break;
                            case 1://edit
                                tagEditText.setText(tag);
                                urlEditText.setText(savedSites.getString(tag, ""));
                                break;
                            case 2: //delete
                                deleteSites(tag);
                                break;
                        }
                    }
                }
        );
        //set the alertDialog negetive button
        builder.setNegativeButton(getString(R.string.cancel), null);
        builder.create().show();//display the alert dialog
        return true;
    }
};
//allow user to choose app for sharing URL of a saved search
private void shareSites(String tag){
    //create the URL representing the search
    String urlString= getString(R.string.search_URL)+Uri.encode(savedSites.getString(tag, ""), "UTF-8");

    //create an intent to share urlString
    Intent shareIntent= new Intent();
    shareIntent.setAction(Intent.ACTION_SEND);
    shareIntent.putExtra(Intent.EXTRA_SUBJECT, getString(R.string.share_subject));
    shareIntent.putExtra(Intent.EXTRA_TEXT,getString(R.string.share_message,urlString));
    shareIntent.setType("text/plain");

    //display app that can share plain text
    startActivity(Intent.createChooser(shareIntent,getString(R.string.share_search)));
}

//delete search after user confirms
private void deleteSites(final String tag){
    //create a new AlertDialog and set its message
    AlertDialog.Builder confirmBuilder= new AlertDialog.Builder(this);
    confirmBuilder.setMessage(getString(R.string.confirm_message, tag));
    //cancel button configration
    confirmBuilder.setNegativeButton(getString(R.string.cancel), null);
    //positive DELETE button
    confirmBuilder.setPositiveButton(getString(R.string.delete),new DialogInterface.OnClickListener(){
                public void onClick(DialogInterface dialog , int id){
                    tags.remove(tag);

                    //remove sharedPerefrences.Editor from Sharedprefrences
                    SharedPreferences.Editor preferenceEditor= savedSites.edit();
                    preferenceEditor.remove(tag);
                    preferenceEditor.apply();

                    adapter.notifyDataSetChanged();
                }
            }
    );
    confirmBuilder.create().show();
    }
  }

这是我的采用者代码

 package com.deitel.favoritesites;

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.List;


public class SitesAdapter extends RecyclerView.Adapter<SitesAdapter.ViewHolder> {
private final View.OnClickListener clickListener;
private final View.OnLongClickListener longClickListener;

private final List<String> tags;


public SitesAdapter(List<String> tags, View.OnClickListener clickListener, View.OnLongClickListener longClickListener) {
    this.tags = tags;
    this.clickListener = clickListener;
    this.longClickListener = longClickListener;
}

public static class ViewHolder extends RecyclerView.ViewHolder {
    public final TextView textView;

    public ViewHolder(View itemView, View.OnClickListener clickListener, View.OnLongClickListener longClickListener) {
        super(itemView);
        textView = (TextView) itemView.findViewById(R.id.textView);

        itemView.setOnClickListener(clickListener);
        itemView.setOnLongClickListener(longClickListener);
    }
}

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item, parent, false);
    return (new ViewHolder(view, clickListener, longClickListener));

}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {
    holder.textView.setText(tags.get(position));
}

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

Answer 1

将您的代码更改为

if (!tags.contains(tag)) {
        tags.add(tag);
        Collections.sort(tags, String.CASE_INSENSITIVE_ORDER);
        adapter.notifyDataSetChanged();
    }

因为，下面的条件总是假的。

if(!tag.contains(tag))

这是因为您正在检查该值本身中是否包含一个值。所以这将永远是真的。

如果您正在检查tag存在于List<String> tags中，您应该这样做。

if(!tags.contains(tag))

Answer 2

将您的代码更改为..。

//add new search to file then refresh all button
private void addTaggedSites(String tag, String query) {
    //get a sharedprefrence editor to store new tag/query pair
    SharedPreferences.Editor preferencesEditor = savedSites.edit();
    preferencesEditor.putString(tag, query);
    preferencesEditor.apply();

    //if tag is new> add and sort tags then display update
    if (!this.tag.contains(tag)) {
        this.tags.add(tag);
        Collections.sort(tags, String.CASE_INSENSITIVE_ORDER);
        adapter.notifyDataSetChanged();
    }
}

Answer 3

这可能有助于：

1. 在适配器中创建一个setter方法，允许您设置/更新适配器ArrayList。
2. 每当您更改列表(即删除标记)时，请通过新的setter方法将更新后的列表传递给适配器。
3. 调用notifyDataSetChanged()。