Android 为什么我得到这个上下文和数据库错误?
我正在努力 创建一个简单的listview,该listview可以填充sqldatabase中的数据。数据库可以工作,我见过它与其他代码一起工作。XML很好,我真的不需要共享它。对于XML,主活动中有两个按钮:new和show。New会将您发送到下一个要添加到列表中的活动。Show将向listview添加数据。主要活动到此为止。另一个名为NewEntry的活动有一个取消按钮和一个保存按钮。它还有三个EditView来帮助您添加数据 问题: 现在,它甚至不能无错误地编译。以下主要活动中列出了这两个错误。如果我注释掉这两个错误,我可以让应用程序运行。当我打开一个新活动并试图保存它时,它崩溃了。它们与上下文有关。我只是有点理解语境的作用,除了它存在于一切事物中这一事实 此错误已解决,请参见底部 这段代码中有两个编译器错误。这是主要的活动。 没有其他编译器错误,只有逻辑错误。 我在评论中已经指出了这些问题 “”数据库管理器无法应用于侦听器“” “无法解析构造函数” 此外,如对上下文有任何解释,将不胜感激Android 为什么我得到这个上下文和数据库错误?,android,database,listview,Android,Database,Listview,我正在努力 创建一个简单的listview,该listview可以填充sqldatabase中的数据。数据库可以工作,我见过它与其他代码一起工作。XML很好,我真的不需要共享它。对于XML,主活动中有两个按钮:new和show。New会将您发送到下一个要添加到列表中的活动。Show将向listview添加数据。主要活动到此为止。另一个名为NewEntry的活动有一个取消按钮和一个保存按钮。它还有三个EditView来帮助您添加数据 问题: 现在,它甚至不能无错误地编译。以下主要活动中列出了这两个
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.view.View.OnClickListener;
import android.widget.ListView;
import android.widget.ArrayAdapter;
import java.util.ArrayList;
public class Main extends Activity {
private DatabaseManager mydManager;
private ListView productRec;
ArrayList<String> tableContent;
private LinearLayout addLayout;
ArrayList<String> arrayAdpt;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
productRec=(ListView)findViewById(R.id.list);
Button newButton = (Button) findViewById(R.id.new_button);
Button showButton = (Button) findViewById(R.id.show_button);
Button newButton = (Button) findViewById(R.id.new_button);
newButton.setOnClickListener(new OnClickListener() {
public void onClick(View n) {
Intent x = new Intent(Main.this.getApplicationContext(), NewEntry.class);
startActivity(x);
}
});
showButton.setOnClickListener(new OnClickListener() { //Want this to launch new intent
public void onClick(View s) {
mydManager = new DatabaseManager(this); // <ERROR:
mydManager.openReadable(); //"DATA BASE MANAGER CANNOT BE APPLIED TO LISTENER"
tableContent = mydManager.retrieveRows();
productRec = (ListView)findViewById(R.id.list);
mydManager.retrieveRows(); //ERROR:
ArrayAdapter<String> arrayAdpt=new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, tableContent); //ERROR:CANNOT RESOLVE CONSTRUCTOR
productRec.setAdapter(arrayAdpt);
productRec.setVisibility(View.VISIBLE);
mydManager.close();
}
});
}
}
导入android.database.sqlite.SQLiteDatabase;
导入android.content.Context;
导入android.content.ContentValues;
导入android.database.Cursor;
导入android.database.sqlite.SQLiteOpenHelper;
导入android.util.Log;
导入java.util.ArrayList;
公共类数据库管理器{
公共静态最终字符串DB_NAME=“shopping”;
公共静态最终字符串DB_TABLE=“products”;
公共静态最终int DB_版本=1;
私有静态最终字符串CREATE_TABLE=“CREATE TABLE”+DB_TABLE+(代码整数主键、产品名称文本、日期浮动);
私人助理;
专用数据库数据库;
私人语境;
公共数据库管理器(上下文c){
this.context=c;
helper=newsqlhelper(c);
this.db=helper.getWritableDatabase();
}
public DatabaseManager openReadable()抛出android.database.SQLException{
helper=newsqlhelper(上下文);
db=helper.getReadableDatabase();
归还这个;
}
公众假期结束(){
helper.close();
}
公共布尔addRow(整数t、字符串a、浮点p){
ContentValues newProduct=新ContentValues();
newProduct.put(“title”,t);
newProduct.put(“作者”,a);
新产品卖出价(“价格”,p);
请尝试{db.insertOrThrow(db_TABLE,null,newProduct);}
捕获(例外e){
Log.e(“插入行时出错”,例如toString());
e、 printStackTrace();
返回false;
}
db.close();
返回true;
}
public ArrayList retrieveRows(){///检索编辑
ArrayList productRows=新的ArrayList();
字符串[]列=新字符串[]{“标题”、“作者”、“价格”};
Cursor Cursor=db.query(db_表,列,null,null,null,null);
cursor.moveToFirst();
while(cursor.isAfterLast()==false){
add(Integer.toString(cursor.getInt(0))+”、“+cursor.getString(1)+”、“+Float.toString(cursor.getFloat(2)));
cursor.moveToNext();
}
if(cursor!=null&!cursor.isClosed()){
cursor.close();
}
返回productRows;
}
公共类SQLHelper扩展了SQLiteOpenHelper{
公共SQLHelper(上下文c){
super(c,DB_名称,null,DB_版本);
}
@凌驾
public void onCreate(SQLiteDatabase db){
db.execSQL(创建_表);
}
@凌驾
public void onUpgrade(SQLiteDatabase db,int-oldVersion,int-newVersion){
Log.w(“产品表”,“升级数据库,即删除表并重新创建它”);
db.execSQL(“如果存在删除表”+db_表);
onCreate(db);
}
}
}
尝试检索行时出错:
04-11 22:08:25.552 21767-21767/com.example.alex.checkbox W/dalvikvm? threadid=1: thread exiting with uncaught exception (group=0x41e7cda0)
04-11 22:08:25.572 21767-21767/com.example.alex.checkbox E/AndroidRuntime? FATAL EXCEPTION: main
Process: com.example.alex.checkbox, PID: 21767
android.database.sqlite.SQLiteException: no such column: title (code 1): , while compiling: SELECT title, author, price FROM products
at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:1113)
at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:690)
at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1448)
at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1295)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1166)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1334)
at com.example.alex.favoritebooks.DatabaseManager.retrieveRows(DatabaseManager.java:56)
at com.example.alex.favoritebooks.Main$2.onClick(Main.java:45)
at android.view.View.performClick(View.java:4654)
at android.view.View$PerformClick.run(View.java:19438)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5487)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
at dalvik.system.NativeStart.main(Native Method)
04-11 22:08:25.552 21767-21767/com.example.alex.checkbox W/dalvikvm?threadid=1:线程以未捕获异常退出(组=0x41e7cda0)
04-11 22:08:25.572 21767-21767/com.example.alex.checkbox E/AndroidRuntime?致命异常:主
进程:com.example.alex.checkbox,PID:21767
android.database.sqlite.SQLiteException:没有这样的列:title(代码1):,编译时:选择title、author、price FROM products
位于android.database.sqlite.SQLiteConnection.nativePrepareStatement(本机方法)
位于android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:1113)
位于android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:690)
位于android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
位于android.database.sqlite.SQLiteProgram.(SQLiteProgram.java:58)
位于android.database.sqlite.SQLiteQuery(SQLiteQuery.java:37)
位于android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
位于android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1448)
位于android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1295)
位于android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1166)
位于android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1334)
在com.example.alex.favoritebooks.DatabaseManager.retrieveRows(DatabaseManager.java:56)
在com.example.alex.favoritebooks.Main$2.onClick(Main.java:45)上
在android.view.view.performClick上(view.java:4654)
在android.view.view$PerformClick.run(view.java:19438)
位于android.os.Handler.handleCallback(Handler.java:733)
This is the database:
import android.database.sqlite.SQLiteDatabase;
import android.content.Context;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import java.util.ArrayList;
public class DatabaseManager {
public static final String DB_NAME = "shopping";
public static final String DB_TABLE = "products";
public static final int DB_VERSION = 1;
private static final String CREATE_TABLE = "CREATE TABLE " + DB_TABLE + " (code INTEGER PRIMARY KEY, product_name TEXT, date FLOAT);";
private SQLHelper helper;
private SQLiteDatabase db;
private Context context;
public DatabaseManager(Context c){
this.context = c;
helper=new SQLHelper(c);
this.db = helper.getWritableDatabase();
}
public DatabaseManager openReadable() throws android.database.SQLException {
helper=new SQLHelper(context);
db = helper.getReadableDatabase();
return this;
}
public void close(){
helper.close();
}
public boolean addRow(int t, String a, float p){
ContentValues newProduct = new ContentValues();
newProduct.put("title", t);
newProduct.put("author", a);
newProduct.put("price", p);
try{db.insertOrThrow(DB_TABLE, null, newProduct);}
catch(Exception e) {
Log.e("Error in inserting rows ", e.toString());
e.printStackTrace();
return false;
}
db.close();
return true;
}
public ArrayList<String> retrieveRows(){ ///Retrieves edit
ArrayList<String> productRows=new ArrayList<String>();
String[] columns = new String[]{"title", "author", "price"};
Cursor cursor = db.query(DB_TABLE, columns, null, null, null, null, null);
cursor.moveToFirst();
while (cursor.isAfterLast() == false) {
productRows.add(Integer.toString(cursor.getInt(0)) + ", "+cursor.getString(1)+", "+Float.toString(cursor.getFloat(2)));
cursor.moveToNext();
}
if (cursor != null && !cursor.isClosed()) {
cursor.close();
}
return productRows;
}
public class SQLHelper extends SQLiteOpenHelper {
public SQLHelper(Context c){
super(c, DB_NAME, null, DB_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w("Products table","Upgrading database i.e. dropping table and recreating it");
db.execSQL("DROP TABLE IF EXISTS " + DB_TABLE);
onCreate(db);
}
}
}
04-11 22:08:25.552 21767-21767/com.example.alex.checkbox W/dalvikvm? threadid=1: thread exiting with uncaught exception (group=0x41e7cda0)
04-11 22:08:25.572 21767-21767/com.example.alex.checkbox E/AndroidRuntime? FATAL EXCEPTION: main
Process: com.example.alex.checkbox, PID: 21767
android.database.sqlite.SQLiteException: no such column: title (code 1): , while compiling: SELECT title, author, price FROM products
at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:1113)
at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:690)
at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1448)
at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1295)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1166)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1334)
at com.example.alex.favoritebooks.DatabaseManager.retrieveRows(DatabaseManager.java:56)
at com.example.alex.favoritebooks.Main$2.onClick(Main.java:45)
at android.view.View.performClick(View.java:4654)
at android.view.View$PerformClick.run(View.java:19438)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5487)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
at dalvik.system.NativeStart.main(Native Method)
newButton.setOnClickListener(new OnClickListener() {
public void onClick(View n) {
// Simply use Main.this on the next line...
Intent x = new Intent(Main.this, NewEntry.class);
startActivity(x);
}
});
showButton.setOnClickListener(new OnClickListener() {
public void onClick(View s) {
mydManager = new DatabaseManager(this); //Here is the error
...
ArrayAdapter<String> arrayAdpt=new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, tableContent);
...
}
});
showButton.setOnClickListener(new OnClickListener() {
public void onClick(View s) {
mydManager = new DatabaseManager(Main.this);
...
arrayAdpt = new ArrayAdapter<String>(Main.this, android.R.layout.simple_list_item_1, tableContent);
...
}
});