同时单击返回按钮主活动未更新

Question

所以我正在尝试做笔记或待办事项应用程序 当我插入数据时，数据入到数据库中，但是当我返回时，它不会在主菜单上更新 所以这是主要活动

package com.frolicfreak.bhushan.memo;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.ContextMenu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
import static com.frolicfreak.bhushan.memo.DatabaseHelper.Table_Name;
import static com.frolicfreak.bhushan.memo.DatabaseHelper.col1;
import static com.frolicfreak.bhushan.memo.DatabaseHelper.col2;
public class MainActivity extends AppCompatActivity implements View.OnClickListener{
FloatingActionButton fab;
DatabaseHelper mydb;
ListView listView;
ArrayAdapter<String> mAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mydb =new DatabaseHelper(this);
fab= (FloatingActionButton)findViewById(R.id.fab);
fab.setOnClickListener(this);
ListView listView = (ListView)findViewById(R.id.list);
registerForContextMenu(listView);
ArrayList<String> theList =new ArrayList<>();
Cursor data= mydb.getAllData();
if (data.getCount()==0){
Toast.makeText(MainActivity.this,"data not inserted",Toast.LENGTH_LONG).show();
}
else
{
while(data.moveToNext()){
theList.add(data.getString(1));
ListAdapter listAdapter=new ArrayAdapter<>(this,android.R.layout.simple_list_item_1,theList);
listView.setAdapter(listAdapter);
}
}
}
@Override
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
super.onCreateContextMenu(menu, v, menuInfo);
if (v.getId()==R.id.list) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu, menu);
}
}
@Override
public boolean onContextItemSelected(MenuItem item) {
AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();
switch(item.getItemId()) {
case R.id.edit:
// edit stuff here
return true;
case R.id.delete:
int count = mydb.deleterow(Table_Name, col1);
return true;
default:
return super.onContextItemSelected(item);
}
}

@Override
public void onClick(View v) {
Intent intent= new Intent(this,Main2Activity.class);
startActivity(intent);
}
}

和 MyDatabaaseHelperjava 文件

package com.frolicfreak.bhushan.memo;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import java.util.ArrayList;
/**
* Created by BHUSHAN on 24-08-2017.
*/
public class DatabaseHelper extends SQLiteOpenHelper {
public static final String Database_Name = "Memo.db";
public static final String Table_Name = "Memo";
public static final String col1 = "ID";
public static final String col2 = "data";

public DatabaseHelper(Context context) {
super(context, Database_Name, null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table " + Table_Name + "(ID integer primary key autoincrement, data text)");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("drop table if exists " + Table_Name);
onCreate(db);
}
public boolean insertData(String data, String Data) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(col2, Data);
long result = db.insert(Table_Name, null, contentValues);
if (result==-1)
return false;
else
return true;
}
public ArrayList<String> getList(){
ArrayList<String> taskList = new ArrayList<>();
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor= db.query(Table_Name,new String[]{col1},new String(col2),null,null,null,null);
while (cursor.moveToNext()){
int index= cursor.getColumnIndex(col1);
taskList.add(cursor.getString(index));
}
cursor.close();
db.close();
return taskList;
}
public Cursor getAllData() {
SQLiteDatabase db = this.getWritableDatabase();
Cursor res = db.rawQuery("SELECT * FROM " + Table_Name, null);
return res;
}

public int deleterow(String table_Name, String col1) {
SQLiteDatabase db = this.getReadableDatabase();
int count = db.delete(Table_Name, DatabaseHelper.col1, null);
return count;
}
}

我的主2活动类

package com.frolicfreak.bhushan.memo;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;
public class Main2Activity extends AppCompatActivity {
DatabaseHelper db;
EditText Data;
FloatingActionButton add;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
db = new DatabaseHelper(this);
Data = (EditText)findViewById(R.id.edit);
add =(FloatingActionButton)findViewById(R.id.add);
AddData();
}
public void AddData(){
add.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
boolean isInserted = db.insertData(Data.getText().toString(),
Data.getText().toString() );
if (isInserted==true)
Toast.makeText(Main2Activity.this,"data inserted",Toast.LENGTH_LONG).show();
else
Toast.makeText(Main2Activity.this,"data not inserted",Toast.LENGTH_LONG).show();
}
}
);
}
}

现在还有一件事我实际上还想编辑和更新数据(选项(，所以如果有人可以帮助我？ 当我从列表中删除任何数据时，当我重新打开应用程序时，所有数据都会被删除 所以也请帮忙 提前致谢

Answer 1

你应该在onResume函数中从数据库中获取数据，而不是在oncreate中。

将此代码添加到您的主活动中

@Override
public void onResume() {
super.onResume(); 
ArrayList<String> theList =new ArrayList<>();
Cursor data= mydb.getAllData();
listView.setAdapter(null);
if (data.getCount()==0){
Toast.makeText(MainActivity.this,"data not inserted",Toast.LENGTH_LONG).show();
}
else
{
while(data.moveToNext()){
theList.add(data.getString(1));
ListAdapter listAdapter=new ArrayAdapter<>(this,android.R.layout.simple_list_item_1,theList);
listView.setAdapter(listAdapter);
}
}
}