好吧，我是android开发的新手
我也遇到了一些已经问过的问题，但我无法解决问题。
所以我正在学习android开发，为了练习，我创建了一个记笔记应用程序，还没有完成，我正在使用SQLite来存储标题和笔记本身之类的信息
我在项目中有三个活动，分别是HomeActivity，MainActivity和EditorActivity，它们的代码我将在下面附加。
所以我认为数据库没有更新并存储新标题。
该应用的预期运行方式： 只有在您第一次运行该应用程序时， mainactivity 才会向您显示有关如何使用该应用程序以及如何设置数据库的说明，此后，无论何时打开该应用程序，您都将直接进入 > homeactivity ，它将在列表视图中显示数据库内容。每当单击此列表视图中的项目时，便会将noteID发送到 editoractivity ，该活动具有两个EditText，一个用于标题，一个用于注释本身。 （目前仅处理标题） 每当标题更改时，都应该更新数据库，但这没有发生。有人可以帮我弄这个吗 ？
代码：
MainActivity.java
package com.dharamshi.noteitdownv2;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.database.sqlite.SQLiteDatabase;
import android.support.constraint.ConstraintLayout;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
int mInstructionsID = 1;
ConstraintLayout mConstraintLayout;
Button mForwardButton;
Button mBackButton;
Button mLetsGo;
LinearLayout mButtonLayout;
SharedPreferences mSharedPreferences;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mSharedPreferences = this.getSharedPreferences(getPackageName(), MODE_PRIVATE );
boolean firstTimeSetup = mSharedPreferences.getBoolean("FirstTimeSetup", false);
if(firstTimeSetup == false) {
initDatabase();
mConstraintLayout = findViewById(R.id.mainLayout);
mForwardButton = findViewById(R.id.forwardButton);
mBackButton = findViewById(R.id.backButton);
mButtonLayout = findViewById(R.id.buttonLayout);
mLetsGo = findViewById(R.id.letsGo);
mLetsGo.setVisibility(View.INVISIBLE);
mButtonLayout.setVisibility(View.VISIBLE);
updateInstructions();
Toast.makeText(this, "Click on the right side of the screen to continue", Toast.LENGTH_LONG).show();
mForwardButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (mInstructionsID <= 4) {
mInstructionsID++;
updateInstructions();
}
}
});
mBackButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (mInstructionsID > 1) {
mInstructionsID--;
updateInstructions();
}
}
});
mLetsGo.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
mSharedPreferences.edit().putBoolean("FirstTimeSetup", true).apply();
Intent intent = new Intent(getApplicationContext(), HomeActivity.class);
startActivity(intent);
finish();
}
});
}else{
Intent intent = new Intent(getApplicationContext(), HomeActivity.class);
startActivity(intent);
finish();
}
}
public void updateInstructions(){
switch (mInstructionsID){
case 1: mConstraintLayout.setBackgroundResource(R.drawable.noteitdownbgone);
break;
case 2: mConstraintLayout.setBackgroundResource(R.drawable.noteitdownbgtwo);
break;
case 3: mConstraintLayout.setBackgroundResource(R.drawable.noteitdownbgthree);
break;
case 4: mConstraintLayout.setBackgroundResource(R.drawable.noteitdownbgfour);
break;
}
if(mInstructionsID > 4)
mInstructionsID = 4;
if(mInstructionsID == 4){
mButtonLayout.setVisibility(View.INVISIBLE);
mLetsGo.setVisibility(View.VISIBLE);
}
}
public void initDatabase(){
try{
SQLiteDatabase myDatabase = openOrCreateDatabase("Notes", MODE_PRIVATE, null);
myDatabase.execSQL("CREATE TABLE IF NOT EXISTS notes (id INT PRIMARY KEY, title TEXT, message TEXT)");
myDatabase.execSQL("INSERT INTO notes (title, message) VALUES ('Introduction', 'This is a introduction')");
Toast.makeText(this, "Database Created!", Toast.LENGTH_SHORT).show();
}catch (Exception e)
{
new AlertDialog.Builder(this)
.setTitle("Error")
.setMessage(e.getMessage())
.setNegativeButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
finish();
}
}).show();
}
}
}
HomeActivity.java
package com.dharamshi.noteitdownv2;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.constraint.ConstraintLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import java.util.ArrayList;
public class HomeActivity extends AppCompatActivity {
ConstraintLayout mainLayout;
public static ArrayList<String> titleList = new ArrayList<>();
public static ArrayList<String> notesList = new ArrayList<>();
public static ArrayList<Integer> idList = new ArrayList<>();
public static ArrayAdapter sArrayAdapter;
ListView notesListView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
titleList.clear();
notesList.clear();
idList.clear();
mainLayout = findViewById(R.id.constraintLayout);
notesListView = findViewById(R.id.notesList);
SQLiteDatabase sqLiteDatabase = openOrCreateDatabase("Notes" , MODE_PRIVATE, null);
Cursor c = sqLiteDatabase.rawQuery("SELECT * FROM notes", null);
int titleIndex = c.getColumnIndex("title");
int idIndex = c.getColumnIndex("id");
int messageIndex = c.getColumnIndex("message");
c.moveToFirst();
if (c != null) {
do {
//Log.i("id", Integer.toString(c.getInt(idIndex)));
idList.add(c.getInt(idIndex));
//Log.i("Title", c.getString(titleIndex));
titleList.add(c.getString(titleIndex));
//Log.i("Message", c.getString(messageIndex));
notesList.add(c.getString(messageIndex));
}while(c.moveToNext());
}
sArrayAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, titleList);
notesListView.setAdapter(sArrayAdapter);
notesListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
Intent intent = new Intent(getApplicationContext(), EditorActivity.class);
intent.putExtra("noteID", i);
startActivity(intent);
}
});
}
}
EditorActivity.java
package com.dharamshi.noteitdownv2;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.widget.EditText;
import android.widget.Toast;
public class EditorActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_editor);
Intent intent = getIntent();
final SQLiteDatabase sqLiteDatabase = openOrCreateDatabase("Notes", MODE_PRIVATE, null);
EditText editTitle = findViewById(R.id.editTitle);
EditText editNote = findViewById(R.id.editNote);
final int noteID =intent.getIntExtra("noteID", -1);
if(noteID != -1)
{
editTitle.setText(HomeActivity.titleList.get(noteID));
editNote.setText(HomeActivity.notesList.get(noteID));
}
editTitle.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
sqLiteDatabase.execSQL("UPDATE notes SET title = '" + charSequence.toString() + "' WHERE id = "+ HomeActivity.idList.get(noteID));
Toast.makeText(EditorActivity.this, "UPDATE notes SET title = '" + charSequence.toString() + "' WHERE id = "+ HomeActivity.idList.get(noteID), Toast.LENGTH_SHORT).show();
HomeActivity.titleList.set(noteID, charSequence.toString());
HomeActivity.sArrayAdapter.notifyDataSetChanged();
}
@Override
public void afterTextChanged(Editable editable) {
}
});
}
}
我也在这里上传了整个程序包：
https://drive.google.com/open?id=1Bc18Bbu0dodXFAQj_MeUrxsHEzCX09zp
编辑： 我在HomeActivity中添加了一个刷新按钮，以验证数据库是否正在更新。结果证明，没有。数据库未更新。
public void refreshList(View view){
idList.clear();
notesList.clear();
titleList.clear();
SQLiteDatabase sqLiteDatabase = openOrCreateDatabase("Notes" , MODE_PRIVATE, null);
Cursor c = sqLiteDatabase.rawQuery("SELECT * FROM notes", null);
int titleIndex = c.getColumnIndex("title");
int idIndex = c.getColumnIndex("id");
int messageIndex = c.getColumnIndex("message");
c.moveToFirst();
if (c != null) {
do {
//Log.i("id", Integer.toString(c.getInt(idIndex)));
idList.add(c.getInt(idIndex));
//Log.i("Title", c.getString(titleIndex));
titleList.add(c.getString(titleIndex));
//Log.i("Message", c.getString(messageIndex));
notesList.add(c.getString(messageIndex));
}while(c.moveToNext());
}
sArrayAdapter.notifyDataSetChanged();
}
答案 0 :(得分：3)
您的问题与使用 id 列有关。首先是如何定义它，然后是如何尝试将ID从HomeActivity传递到EditorActivity。
将列定义为id INT PRIMARY KEY并不会获得分配唯一ID的理想结果（先分配1，然后可能2，然后再分配3等）。
您必须非常明确，并使用id INTEGER PRIMARY KEY，然后将其定义为 rowid 的别名，如果未指定任何值，则它将是唯一的ID
要解决此问题，请更改：-
myDatabase.execSQL("CREATE TABLE IF NOT EXISTS notes (id INT PRIMARY KEY, title TEXT, message TEXT)");
至：-
myDatabase.execSQL("CREATE TABLE IF NOT EXISTS notes (id INTEGER PRIMARY KEY, title TEXT, message TEXT)");
第二个问题是，在HomeActivity的onItemClick中，您正在传递项目在列表中的位置，然后检索该值，就好像它是id一样。没有解决问题1，所有行的ID将为null，该位置将永远不匹配null，因此您将永远不会更新行。
但是，即使ID的位置更正，该行也不会与所单击的行/项目的ID相匹配。也就是说，分配的第一个id将为1，第一行的位置为0，依此类推。
好消息是您拥有三个ArrayList，因此位置将等于idList的第n个元素，因此修复相对简单。您只需要更改：-
intent.putExtra("noteID", i);
至：-
intent.putExtra("noteID", idList.get(i));
使用：-
your_cursor.moveToFirst();
if (your_cursor != null) {
.....
}
可能会导致出现问题，因为您的光标不会为空。游标可能为空，在这种情况下，getCount()方法将返回0，或者任何moveTo???方法将返回false。
我建议更换：-
Cursor c = sqLiteDatabase.rawQuery("SELECT * FROM notes", null);
int titleIndex = c.getColumnIndex("title");
int idIndex = c.getColumnIndex("id");
int messageIndex = c.getColumnIndex("message");
c.moveToFirst(); // <<<< NO
if (c != null) { // <<<< Cursor will not be null does nothing to check
do {
//Log.i("id", Integer.toString(c.getInt(idIndex)));
idList.add(c.getInt(idIndex));
//Log.i("Title", c.getString(titleIndex));
titleList.add(c.getString(titleIndex));
//Log.i("Message", c.getString(messageIndex));
notesList.add(c.getString(messageIndex));
}while(c.moveToNext());
}
更紧凑：-
Cursor c = sqLiteDatabase.rawQuery("SELECT * FROM notes", null);
while(c.moveToNext()) {
idList.add(c.getInt(c.getColumnIndex("id")));
titleList.add(c.getString(c.getColumnIndex("title")));
notesList.add(c.getString(c.getColumnIndex("message")));
}
You are updating the database every time a a change is made (i.e. every time a character is typed or removed). You may find this rather intensive (especially with a Toast).
请注意，此阶段的更改不会立即反映出来，但是如果您重新启动应用程序，则应该看到数据已更新。
更多……..
以下是用于实现解决方案的完整代码，该解决方案在项目被编辑后不会更改。 ：-
这会将ID传递给EditorActivity，并使用 onResume 方法来重建列表。
public class HomeActivity extends AppCompatActivity {
ConstraintLayout mainLayout;
public static ArrayList<String> titleList = new ArrayList<>();
public static ArrayList<String> notesList = new ArrayList<>();
public static ArrayList<Integer> idList = new ArrayList<>();
public static ArrayAdapter sArrayAdapter;
SQLiteDatabase sqLiteDatabase; //<<<< ADDED
ListView notesListView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
titleList.clear();
notesList.clear();
idList.clear();
mainLayout = findViewById(R.id.constraintLayout);
notesListView = findViewById(R.id.notesList);
sqLiteDatabase = openOrCreateDatabase("Notes" , MODE_PRIVATE, null); // <<<< CHANGED
Cursor c = sqLiteDatabase.rawQuery("SELECT * FROM notes", null);
/*
int titleIndex = c.getColumnIndex("title");
int idIndex = c.getColumnIndex("id");
int messageIndex = c.getColumnIndex("message");
c.moveToFirst(); // <<<< NO
if (c != null) { // <<<< Cursor will not be null does nothing to check
do {
//Log.i("id", Integer.toString(c.getInt(idIndex)));
idList.add(c.getInt(idIndex));
//Log.i("Title", c.getString(titleIndex));
titleList.add(c.getString(titleIndex));
//Log.i("Message", c.getString(messageIndex));
notesList.add(c.getString(messageIndex));
}while(c.moveToNext());
}
*/
while(c.moveToNext()) {
idList.add(c.getInt(c.getColumnIndex("id")));
titleList.add(c.getString(c.getColumnIndex("title")));
notesList.add(c.getString(c.getColumnIndex("message")));
}
sArrayAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, titleList);
notesListView.setAdapter(sArrayAdapter);
notesListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
Intent intent = new Intent(getApplicationContext(), EditorActivity.class);
//intent.putExtra("noteID", i); // <<<< i is the position not the ID of the row
intent.putExtra("noteID", idList.get(i)); //<<<< ADDED
startActivity(intent);
}
});
}
//<<<<<<<<<< Added to rebuild the Arrays and to notify the adapter of the changed data
protected void onResume() {
super.onResume();
Cursor c = sqLiteDatabase.rawQuery("SELECT * FROM notes", null);
idList.clear();
notesList.clear();
titleList.clear();
while(c.moveToNext()) {
idList.add(c.getInt(c.getColumnIndex("id")));
titleList.add(c.getString(c.getColumnIndex("title")));
notesList.add(c.getString(c.getColumnIndex("message")));
}
sArrayAdapter.notifyDataSetChanged();
}
}
这具有相当广泛的更改，包括方法 setEditTexts ，用于根据传递的 id 获取值。而且，许多变量的范围已更改为类级别。
public class EditorActivity extends AppCompatActivity {
SQLiteDatabase sqLiteDatabase; //<<<< ADDED
EditText editTitle, editNote; //<<<< ADDED
int noteID; //<<<< ADDED
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_editor);
Intent intent = getIntent();
sqLiteDatabase = openOrCreateDatabase("Notes", MODE_PRIVATE, null); //<<<< CHANGED
editTitle = findViewById(R.id.editTitle); //<<<< CHANGED
editNote = findViewById(R.id.editNote); //<<<< CHANGED
noteID =intent.getIntExtra("noteID", -1); //<<<<CHANGED
if(noteID != -1)
{
setEditTexts(noteID); //<<<< ADDED
//editTitle.setText(HomeActivity.titleList.get(noteID)); //<<<< DELETED
//editNote.setText(HomeActivity.notesList.get(noteID)); //<<<< DELETED
}
editTitle.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
String sql = "UPDATE notes SET title = '" + charSequence.toString() + "' WHERE id="+ String.valueOf(noteID); //<<<< CHANGED
sqLiteDatabase.execSQL(sql); //<<<< CHANGED
Toast.makeText(EditorActivity.this, sql, Toast.LENGTH_SHORT).show(); //<<<< CHANGED
//HomeActivity.titleList.set(noteID, charSequence.toString()); //<<<<DELETED done in onResume of HomeActivity
//HomeActivity.sArrayAdapter.notifyDataSetChanged(); //<<<<DELETED done in onResume of HomeActivity
}
@Override
public void afterTextChanged(Editable editable) {
}
});
}
//<<<<<<<<<< ADDED
private void setEditTexts(int id) {
String whereclasue = "id=?";
String[] whereargs = new String[]{String.valueOf(id)};
Cursor c = sqLiteDatabase.query(
"notes",
null,
whereclasue,
whereargs,
null,null,null,null
);
if (c.moveToFirst()) {
editTitle.setText(c.getString(c.getColumnIndex("title")));
editNote.setText(c.getString(c.getColumnIndex("message")));
}
}
}
答案 1 :(得分：0)
尝试更改此行：
myDatabase.execSQL("CREATE TABLE IF NOT EXISTS notes (id INT PRIMARY KEY, title TEXT, message TEXT)");
收件人
myDatabase.execSQL("CREATE TABLE IF NOT EXISTS notes (id INTEGER PRIMARY KEY, title TEXT, message TEXT)");