道歉首先是因为这将是一个很长的问题。
我正在创建一个待办事项列表，使用2个片段中的2个RecyclerViews代码。
MainActivity.java
public class MainActivity extends AppCompatActivity {
/**
* The {@link android.support.v4.view.PagerAdapter} that will provide
* fragments for each of the sections. We use a
* {@link FragmentPagerAdapter} derivative, which will keep every
* loaded fragment in memory. If this becomes too memory intensive, it
* may be best to switch to a
* {@link android.support.v4.app.FragmentStatePagerAdapter}.
*/
private SectionsPagerAdapter mSectionsPagerAdapter;
private ViewPager mViewPager;
private TaskDbHelper mHelper;
public Tab1 incompleteTasks;
public Tab2 completedTasks;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.container);
mViewPager.setAdapter(mSectionsPagerAdapter);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(mViewPager);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
try{
final EditText taskEditText = new EditText(MainActivity.this);
AlertDialog dialog = new AlertDialog.Builder(MainActivity.this)
.setTitle("Add a new task")
.setMessage("What do you want to do next?")
.setView(taskEditText)
.setPositiveButton("Add", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
try{
mHelper = new TaskDbHelper(MainActivity.this);
String task = String.valueOf(taskEditText.getText());
mHelper.adddata(MainActivity.this, task);
//incompleteTasks.addTask(mHelper.getAddedTask("0").get(0));
incompleteTasks.updateUI();
}
catch(Exception ex1){
Toast.makeText(MainActivity.this, (String)ex1.getMessage(), Toast.LENGTH_LONG).show();
}
}
})
.setNegativeButton("Cancel", null)
.create();
dialog.show();
}catch (Exception ex) {
Log.d("MainActivity", "Exception: " + ex.getMessage());
}
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, 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.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a PlaceholderFragment (defined as a static inner class below).
switch (position){
case 0:
//Tab1 incompleteTasks = new Tab1();
incompleteTasks = new Tab1();
incompleteTasks.setContext(MainActivity.this);
return incompleteTasks;
case 1:
//Tab2 completedTasks = new Tab2();
completedTasks = new Tab2();
completedTasks.setContext(MainActivity.this);
return completedTasks ;
default:
return null;
}
}
@Override
public int getItemPosition(Object object) {
// POSITION_NONE makes it possible to reload the PagerAdapter
return POSITION_NONE;
}
@Override
public int getCount() {
// Show 3 total pages.
return 2;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "Incomplete";
case 1:
return "Completed";
}
return null;
}
}
}
RecyclerAdapter.java
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.TaskHolder> {
private ArrayList<Task> mTasks;
private boolean completedStatus;
private Context contextFromTab;
private int lastPosition = -1;
private RecyclerViewAnimator mAnimator;
//1
public class TaskHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
//2
private TextView mTask_id;
private TextView mTask_title;
private TextView mTask_created_date;
private ImageButton mImageButtonDone;
private ImageButton mImageButtonUndo;
private ImageButton mImageButtonEdit;
private ImageButton mImageButtonDelete;
//3
//private static final String PHOTO_KEY = "PHOTO";
//4
public TaskHolder(View v) {
super(v);
try{
//v.geti
mTask_id = v.findViewById(R.id.task_id);
mTask_title = v.findViewById(R.id.task_title);
mTask_created_date = v.findViewById(R.id.task_created_date);
mImageButtonDone = v.findViewById(R.id.imageButtonDone);
mImageButtonUndo = v.findViewById(R.id.imageButtonUndo);
mImageButtonEdit = v.findViewById(R.id.imageButtonEdit);
mImageButtonDelete = v.findViewById(R.id.imageButtonDelete);
v.setOnClickListener(this);
mImageButtonDone.setOnClickListener(this);
mImageButtonUndo.setOnClickListener(this);
mImageButtonEdit.setOnClickListener(this);
mImageButtonDelete.setOnClickListener(this);
//v.setAnimation();
}
catch (Exception ex){
Log.d("TaskHolder", ex.getMessage());
}
}
//5
@Override
public void onClick(View v) {
if(v.equals(mImageButtonDone)){
View parent = (View) v.getParent();
TextView taskTextView = (TextView) parent.findViewById(R.id.task_id);
String _id = String.valueOf(taskTextView.getText());
TaskDbHelper mHelper = new TaskDbHelper(contextFromTab);
mHelper.changeTaskStatus(contextFromTab,true, _id);
removeAt(getAdapterPosition());
}
else if(v.equals(mImageButtonUndo)) {
View parent = (View) v.getParent();
TextView taskTextView = parent.findViewById(R.id.task_id);
String _id = String.valueOf(taskTextView.getText());
TaskDbHelper mHelper = new TaskDbHelper(contextFromTab);
mHelper.changeTaskStatus(contextFromTab,false, _id);
}
else if(v.equals(mImageButtonEdit)) {
View parent = (View) v.getParent();
TextView taskIdTextView = (TextView) parent.findViewById(R.id.task_id);
TextView taskTitleTextView = (TextView) parent.findViewById(R.id.task_title);
final String _id = String.valueOf(taskIdTextView.getText());
String _title = String.valueOf(taskTitleTextView.getText());
/*Intent intent = new Intent(this, TaskDetails.class);
intent.putExtra("_id", _id);
intent.putExtra("_title", _title);
startActivity(intent);*/
try{
final EditText taskEditText = new EditText(contextFromTab);
taskEditText.setText(_title);
AlertDialog dialog = new AlertDialog.Builder(contextFromTab)
.setTitle("Edit task")
.setView(taskEditText)
.setPositiveButton("Done", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
try{
TaskDbHelper mHelper = new TaskDbHelper(contextFromTab);
String task = String.valueOf(taskEditText.getText());
mHelper.editTask(contextFromTab, task, _id);
updateAt(getAdapterPosition(), _id);
/*Tab1 tab1 = new Tab1();
tab1.setContext(MainActivity.this);
tab1.updateUI();*/
}
catch(Exception ex1){
Toast.makeText(contextFromTab, (String)ex1.getMessage(), Toast.LENGTH_LONG).show();
}
}
})
.setNegativeButton("Cancel", null)
.create();
dialog.show();
}catch (Exception ex) {
Log.d("MainActivity", "Exception: " + ex.getMessage());
}
}
else if(v.equals(mImageButtonDelete)) {
View parent = (View) v.getParent();
TextView taskTextView = (TextView) parent.findViewById(R.id.task_id);
String _id = String.valueOf(taskTextView.getText());
TaskDbHelper mHelper = new TaskDbHelper(contextFromTab);
mHelper.deleteTask(_id);
removeAt(getAdapterPosition());
}
Log.d("RecyclerView", "CLICK!");
}
public void bindTask(Task task, boolean completedStatus) {
try{
mTask_id.setText(Integer.toString(task._id) );
mTask_title.setText(task.title);
mTask_created_date.setText("created on: " + task.created_datetime);
if(completedStatus){
mImageButtonDone.setVisibility(View.INVISIBLE);
mImageButtonUndo.setVisibility(View.VISIBLE);
}else{
mImageButtonDone.setVisibility(View.VISIBLE);
mImageButtonUndo.setVisibility(View.INVISIBLE);
}
}
catch (Exception ex){
Log.d("bindTask", ex.getMessage());
}
}
public void addTask(Task task){
mTasks.add(0, task);
notifyItemInserted(0);
//smoothScrollToPosition(0);
}
public void removeAt(int position) {
mTasks.remove(position);
notifyItemRemoved(position);
notifyItemRangeChanged(position, getItemCount());
}
public void updateAt(int position, String task_id){
//mTasks.
//mTasks.set(position);
try{
TaskDbHelper mHelper = new TaskDbHelper(contextFromTab);
Task updatedTask = mHelper.getTaskById(task_id);
mTasks.set(position, updatedTask);
notifyItemChanged(position);
}
catch (Exception ex){
}
}
}
public RecyclerAdapter(ArrayList<Task> tasks, boolean tasksCompletedStatus, Context context, RecyclerView recyclerView) {
mTasks = tasks;
completedStatus = tasksCompletedStatus;
contextFromTab = context;
mAnimator = new RecyclerViewAnimator(recyclerView);
}
@Override
public RecyclerAdapter.TaskHolder onCreateViewHolder(ViewGroup parent, int viewType) {
try{
View inflatedView = LayoutInflater.from(parent.getContext())
.inflate(R.layout.item_todo, parent, false);
mAnimator.onCreateViewHolder(inflatedView);
return new TaskHolder(inflatedView);
}
catch(Exception ex){
Log.d("onCreateViewHolder", ex.getMessage());
return null;
}
}
private void setAnimation(View viewToAnimate, int position)
{
// If the bound view wasn't previously displayed on screen, it's animated
if (position > lastPosition)
{
Animation animation = AnimationUtils.loadAnimation(contextFromTab, android.R.anim.slide_in_left);
animation.setDuration(3000);
viewToAnimate.startAnimation(animation);
lastPosition = position;
}
}
@Override
public void onBindViewHolder(RecyclerAdapter.TaskHolder holder, int position) {
try{
Task itemTask = mTasks.get(position);
holder.bindTask(itemTask, completedStatus);
mAnimator.onBindViewHolder(holder.itemView, position);
}
catch(Exception ex){
Log.d("onBindViewHolder", ex.getMessage());
}
}
@Override
public int getItemCount() {
try{
return mTasks.size();
}
catch(Exception ex){
Log.d("getItemCount", ex.getMessage());
return 0;
}
}
public ArrayList<Task> getListTasks(){
return mTasks;
}
}
TaskDBHelper.java
public class TaskDbHelper extends SQLiteOpenHelper{
// Table Name
public static final String TABLE_NAME = "tasks";
// Table columns
public static final String _ID = "_id";
public static final String COL_TASK_TITLE = "title";
public static final String COL_TASK_PARENT_ID = "parent_id";
public static final String COL_TASK_COMPLETED_STATUS = "completed_status";
public static final String COL_TASK_CREATED_DATETIME = "created_datetime";
public static final String COL_TASK_MODIFIED_DATETIME = "modified_datetime";
// Database Information
static final String DB_NAME = "com.sagarmhatre.simpletodo";
// database version
static final int DB_VERSION = 1;
public TaskDbHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
try {
String createTable = "CREATE TABLE " + TABLE_NAME + " ( " +
_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
COL_TASK_TITLE + " TEXT NOT NULL," +
COL_TASK_PARENT_ID + " INTEGER DEFAULT 0," +
COL_TASK_COMPLETED_STATUS + " BOOLEAN DEFAULT 0," +
COL_TASK_CREATED_DATETIME + " DATETIME DEFAULT (DATETIME(CURRENT_TIMESTAMP, 'LOCALTIME'))," +
COL_TASK_MODIFIED_DATETIME + " DATETIME" +");";
db.execSQL(createTable);
}
catch (Exception ex){
Log.d("TaskDbHelper", "Exception: " + ex.getMessage());
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
//Insert Value
public void adddata(Context context,String task_title) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(COL_TASK_TITLE, task_title);
db.insert(TABLE_NAME, null, values);
db.close();
}
public Task adddataWithReturnTask(Context context,String task_title) {
try{
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(COL_TASK_TITLE, task_title);
db.insert(TABLE_NAME, null, values);
db.close();
ArrayList<Task> taskList = this.getAddedTask("0");
return taskList.get(0);
}
catch(Exception ex){
Log.d("MainActivity", "Exception: " + ex.getMessage());
return null;
}
}
//Delete Query
public void deleteTask(String id) {
String deleteQuery = "DELETE FROM " + TABLE_NAME + " where " + _ID + "= " + id ;
SQLiteDatabase db = this.getReadableDatabase();
db.execSQL(deleteQuery);
}
public void changeTaskStatus(Context context,Boolean taskStatus, String id) {
try{
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
if(taskStatus)
values.put(COL_TASK_COMPLETED_STATUS, 1);
else
values.put(COL_TASK_COMPLETED_STATUS, 0);
db.update(TABLE_NAME, values, _ID + "=" + id, null);
db.close();
}
catch(Exception ex){
Log.d("changeTaskStatus() ", "Exception: " + ex.getMessage());
}
}
// Edit task - by me
public void editTask(Context context,String task_title, String id) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(COL_TASK_TITLE, task_title);
db.update(TABLE_NAME, values, _ID + "=" + id, null);
db.close();
}
//Get Row Count
public int getCount() {
String countQuery = "SELECT * FROM " + TABLE_NAME;
int count = 0;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
if(cursor != null && !cursor.isClosed()){
count = cursor.getCount();
cursor.close();
}
return count;
}
//Get FavList
public ArrayList<Task> getTaskList(String ParentID, Boolean completedStatus){
try{
String selectQuery;
if(completedStatus){
selectQuery = "SELECT * FROM " + TABLE_NAME + " WHERE "+ COL_TASK_PARENT_ID + "="+ParentID+ " AND " + COL_TASK_COMPLETED_STATUS + " = " + 1 + " ORDER BY " + _ID + " DESC";
}else{
selectQuery = "SELECT * FROM " + TABLE_NAME + " WHERE "+ COL_TASK_PARENT_ID + "="+ParentID+ " AND " + COL_TASK_COMPLETED_STATUS + " = " + 0 + " ORDER BY " + _ID + " DESC";
}
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
ArrayList<Task> TaskList = new ArrayList<Task>();
if (cursor.moveToFirst()) {
do {
Task task = new Task();
task._id = Integer.parseInt(cursor.getString(cursor.getColumnIndex(_ID)));
task.title = cursor.getString(1);
task.parent_id = Integer.parseInt(cursor.getString(2));
task.completed_status = Boolean.parseBoolean(cursor .getString(3));
task.created_datetime = cursor.getString(4);
task.modified_datetime = cursor.getString(5);
TaskList.add(task);
} while (cursor.moveToNext());
}
return TaskList;
}
catch(Exception ex){
Log.d("getTaskList() ", "Exception: " + ex.getMessage());
return null;
}
}
public Task getTaskById(String _id){
try{
String selectQuery;
selectQuery = "SELECT * FROM " + TABLE_NAME + " WHERE "+ _ID + "="+_id;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
ArrayList<Task> TaskList = new ArrayList<Task>();
if (cursor.moveToFirst()) {
do {
Task task = new Task();
task._id = Integer.parseInt(cursor.getString(cursor.getColumnIndex(_ID)));
task.title = cursor.getString(1);
task.parent_id = Integer.parseInt(cursor.getString(2));
task.completed_status = Boolean.parseBoolean(cursor .getString(3));
task.created_datetime = cursor.getString(4);
task.modified_datetime = cursor.getString(5);
TaskList.add(task);
} while (cursor.moveToNext());
}
return TaskList.get(0);
}
catch(Exception ex){
Log.d("getTaskList() ", "Exception: " + ex.getMessage());
return null;
}
}
public ArrayList<Task> getAddedTask(String ParentID){
try{
String selectQuery;
selectQuery = "SELECT * FROM " + TABLE_NAME + " WHERE "+ COL_TASK_PARENT_ID + "="+ParentID+ " AND " + COL_TASK_COMPLETED_STATUS + " = " + 0 + " ORDER BY " + _ID + " DESC";
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
ArrayList<Task> TaskList = new ArrayList<Task>();
if (cursor.moveToFirst()) {
do {
Task task = new Task();
task._id = Integer.parseInt(cursor.getString(cursor.getColumnIndex(_ID)));
task.title = cursor.getString(1);
task.parent_id = Integer.parseInt(cursor.getString(2));
task.completed_status = Boolean.parseBoolean(cursor .getString(3));
task.created_datetime = cursor.getString(4);
task.modified_datetime = cursor.getString(5);
TaskList.add(task);
} while (cursor.moveToNext());
}
return TaskList;
}
catch(Exception ex){
Log.d("getTaskList() ", "Exception: " + ex.getMessage());
return null;
}
}
}
Tab1.java
public class Tab1 extends Fragment {
private static final String TAG = "Tab1";
private TaskDbHelper mHelper;
//int listResourceID;
//ViewAdapter viewAdapter;
Context incompleteListContext;
Toolbar toolbar;
private RecyclerView mRecyclerView;
private LinearLayoutManager mLinearLayoutManager;
RecyclerAdapter adapter;
public void setContext(Context context){
this.incompleteListContext = context;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.tab1, container, false);
mRecyclerView = rootView.findViewById(R.id.list_todo);
mRecyclerView.setHasFixedSize(true);
//mRecyclerView.setItemAnimator(new SlideInLeftAnimator());
//SlideInUpAnimator animator = new SlideInUpAnimator(new OvershootInterpolator());
//mRecyclerView.setItemAnimator(animator);
mLinearLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(mLinearLayoutManager);
updateUI();
return rootView;
}
//@Override
//public void onViewCreated(View rootView, Bundle savedInstanceState){
//incompleteList = rootView.findViewById(R.id.list_todo_completed);
//updateUI();
//}
public void updateUI() {
try {
mHelper = new TaskDbHelper(incompleteListContext);
ArrayList<Task> taskList = mHelper.getTaskList("0",false);
adapter = new RecyclerAdapter(taskList, false, incompleteListContext, mRecyclerView);
mRecyclerView.setAdapter(adapter);
}
catch (Exception ex) {
Log.d(TAG, "Exception: " + ex.getMessage());
}
}
public RecyclerView getRecyclerView(){
return mRecyclerView;
}
}
到目前为止，我成功实现了删除和更新操作，而无需重新加载Tab1中的整个列表。但是在添加项目之后我想将它添加到顶部，我无法在大多数RecyclerView教程中看到它。所以我目前正在重新加载整个列表（我知道这不合适）。
需要一种不加载整个列表并在列表顶部添加项目的方法。 作为Android开发的新手，欢迎任何形式的帮助。
答案 0 :(得分：1)
阅读您的代码有点困难 - ＆gt;请不要混合使用camelcase pascalcase前缀和非前缀命名变量。
要在顶部添加项目，请尝试使用（PSEUDO CODE）：
items.add(0, ITEM_HERE);
adapter.notifyDataSetChanged();
recyclerView.smoothScrollToPosition(0);
这个addTask方法不能像你想要的那样工作吗？
public void addTask(Task task){
mTasks.add(0, task);
notifyItemInserted(0);
smoothScrollToPosition(0);
}