Java 在android中从sqlite数据库检索数据时发生运行时错误
我试图使用sqlite在eclipse中插入和检索数据库中的数据,但它显示了一个Java 在android中从sqlite数据库检索数据时发生运行时错误,java,android,sqlite,Java,Android,Sqlite,我试图使用sqlite在eclipse中插入和检索数据库中的数据,但它显示了一个运行时错误。我创建了一个布局,有三个编辑文本和一个按钮来创建简单的信息,但没有创建任何内容。我使用以下代码创建java数据库: package com.example.databasetest; import android.content.ContentValues; import android.content.Context; import android.database.SQLException; i
运行时错误
。我创建了一个布局,有三个编辑文本和一个按钮来创建简单的信息,但没有创建任何内容。我使用以下代码创建java数据库:
package com.example.databasetest;
import android.content.ContentValues;
import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DBHelper extends SQLiteOpenHelper{
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "teacher";
private static final String TABLE_NAME = "teacher_table";
private static final String NAME = "teacher_name";
private static final String FATHER_NAME = "father_name";
private static final String MOTHER_NAME = "mother_name";
SQLiteDatabase data=this.getWritableDatabase();
Context ctx;
public DBHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
ctx=context;
Log.d("DATABASE OPERATION", "DATABASE CREATED");
}
@Override
public void onCreate(SQLiteDatabase db) {
data=db;
db.execSQL("CREATE TABLE " + TABLE_NAME + " ("
+ NAME + " TEXT,"
+ FATHER_NAME + " TEXT,"
+ MOTHER_NAME + " INTEGER,"
+ ");");
Log.d("DATABASE OPERATION", "TABLE CREATED");
}
public void open() throws SQLException
{
DBHelper db1 = new DBHelper(ctx);
data = db1.getWritableDatabase();
}
public void close()
{
data.close();
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXCEPTION EXISTS");
onCreate(db);
}
public void onInsert(DBHelper db,String name,String f_name, String m_name)
{
SQLiteDatabase sql= db.getWritableDatabase();
ContentValues cv=new ContentValues();
cv.put("teacher_name",name);
cv.put("father_name", f_name);
cv.put("mother_name", m_name);
sql.insert(TABLE_NAME, null, cv);
Log.d("DATABASE OPERATION", "ONE ROW INSERTED.....");
}
}
和java文件作为
package com.example.databasetest;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends Activity {
EditText NAME,FATHER,MOTHER,ID;
String name,father,mother,id;
int i=1;
Button save;
Context ctxx;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
NAME=(EditText)findViewById(R.id.name);
FATHER=(EditText)findViewById(R.id.father_name);
MOTHER=(EditText)findViewById(R.id.mother_name);
ID=(EditText)findViewById(R.id.emp_id);
save=(Button)findViewById(R.id.submit);
save.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
id=ID.getText().toString();
name=NAME.getText().toString();
father=FATHER.getText().toString();
mother=MOTHER.getText().toString();
if(id.equals(i))
{
Toast.makeText(getBaseContext(), "not allow insertion", Toast.LENGTH_LONG).show();
}
else
{
DBHelper DB=new DBHelper(ctxx);
DB.open();
DB.onInsert(DB, name, father, mother);
Toast.makeText(getBaseContext(), "insertion sucessful", Toast.LENGTH_LONG).show();
finish();
}
}
});
}
}
当我点击log cat中的按钮时,显示运行时错误
05-08 02:54:05.932: D/AndroidRuntime(922): Shutting down VM
05-08 02:54:05.999: W/dalvikvm(922): threadid=1: thread exiting with uncaught exception (group=0x41465700)
05-08 02:54:06.189: E/AndroidRuntime(922): FATAL EXCEPTION: main
05-08 02:54:06.189: E/AndroidRuntime(922): java.lang.NullPointerException
05-08 02:54:06.189: E/AndroidRuntime(922): at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
05-08 02:54:06.189: E/AndroidRuntime(922): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
05-08 02:54:06.189: E/AndroidRuntime(922): at com.example.databasetest.DBHelper.<init>(DBHelper.java:22)
05-08 02:54:06.189: E/AndroidRuntime(922): at com.example.databasetest.MainActivity$1.onClick(MainActivity.java:49)
05-08 02:54:06.189: E/AndroidRuntime(922): at android.view.View.performClick(View.java:4240)
05-08 02:54:06.189: E/AndroidRuntime(922): at android.view.View$PerformClick.run(View.java:17721)
05-08 02:54:06.189: E/AndroidRuntime(922): at android.os.Handler.handleCallback(Handler.java:730)
05-08 02:54:06.189: E/AndroidRuntime(922): at android.os.Handler.dispatchMessage(Handler.java:92)
05-08 02:54:06.189: E/AndroidRuntime(922): at android.os.Looper.loop(Looper.java:137)
05-08 02:54:06.189: E/AndroidRuntime(922): at android.app.ActivityThread.main(ActivityThread.java:5103)
05-08 02:54:06.189: E/AndroidRuntime(922): at java.lang.reflect.Method.invokeNative(Native Method)
05-08 02:54:06.189: E/AndroidRuntime(922): at java.lang.reflect.Method.invoke(Method.java:525)
05-08 02:54:06.189: E/AndroidRuntime(922): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
05-08 02:54:06.189: E/AndroidRuntime(922): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
05-08 02:54:06.189: E/AndroidRuntime(922): at dalvik.system.NativeStart.main(Native Method)
05-08 02:54:09.589: I/Process(922): Sending signal. PID: 922 SIG: 9
05-08 02:54:05.932:D/AndroidRuntime(922):关闭虚拟机
05-08 02:54:05.999:W/dalvikvm(922):threadid=1:线程以未捕获异常退出(组=0x41465700)
05-08 02:54:06.189:E/AndroidRuntime(922):致命异常:主
05-08 02:54:06.189:E/AndroidRuntime(922):java.lang.NullPointerException
05-08 02:54:06.189:E/AndroidRuntime(922):在android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
05-08 02:54:06.189:E/AndroidRuntime(922):位于android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
05-08 02:54:06.189:E/AndroidRuntime(922):位于com.example.databasetest.DBHelper.(DBHelper.java:22)
05-08 02:54:06.189:E/AndroidRuntime(922):在com.example.databasetest.MainActivity$1.onClick(MainActivity.java:49)
05-08 02:54:06.189:E/AndroidRuntime(922):在android.view.view.performClick(view.java:4240)
05-08 02:54:06.189:E/AndroidRuntime(922):在android.view.view$PerformClick.run(view.java:17721)
05-08 02:54:06.189:E/AndroidRuntime(922):在android.os.Handler.handleCallback(Handler.java:730)上
05-08 02:54:06.189:E/AndroidRuntime(922):在android.os.Handler.dispatchMessage(Handler.java:92)上
05-08 02:54:06.189:E/AndroidRuntime(922):在android.os.Looper.loop(Looper.java:137)上
05-08 02:54:06.189:E/AndroidRuntime(922):位于android.app.ActivityThread.main(ActivityThread.java:5103)
05-08 02:54:06.189:E/AndroidRuntime(922):位于java.lang.reflect.Method.Invokenactive(本机方法)
05-08 02:54:06.189:E/AndroidRuntime(922):位于java.lang.reflect.Method.invoke(Method.java:525)
05-08 02:54:06.189:E/AndroidRuntime(922):在com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
05-08 02:54:06.189:E/AndroidRuntime(922):位于com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
05-08 02:54:06.189:E/AndroidRuntime(922):在dalvik.系统NativeStart.main(本机方法)
05-08 02:54:09.589:I/进程(922):发送信号。PID:922信号:9
ctxx
从未初始化,这可能是导致崩溃的原因。一般来说,在处理活动和片段子类时,几乎不需要保留对上下文的引用。活动是上下文
的一个子类,通常这个
就足够了。在片段中,您可以使用getActivity()
圣歌
DBHelper DB=new DBHelper(ctxx);
与
正如@DerGolem所指出的,您正在为列MOTHER\u NAME
使用整型。您可能希望使用文本
,并且还需要一个主键“\u id”
在活动中,在onCreate中初始化ctxx: ctxx=这个 或 DBHelper DB=新的DBHelper(MainActivity.this) 每当初始化数据库对象时,都会出现sqlite锁定异常。也可以解决此问题
public void onCreate(SQLiteDatabase db) {
data=db;
db.execSQL("CREATE TABLE " + TABLE_NAME + " ("
+ NAME + " TEXT,"
+ FATHER_NAME + " TEXT,"
+ MOTHER_NAME + " TEXT"
+ ");");
Log.d("DATABASE OPERATION", "TABLE CREATED");
}
对于整数,
删除
像这样初始化它
DBHelper DB=new DBHelper(MainActivity.this);
在onCreate()方法中需要init ctxx:
如果你想了解更多关于android上的sqlite->ok。但是如果你想减少代码,你可以尝试一些android的SqliteLibrary。(例如ActiveAndroid,GreenDAO…)。@Blackbelt您应该删除“,”。。。这是一个表格创建我如何从一个表格到另一个表格检索数据请随意提问,您的
ctxx
尚未初始化。尝试DBHelper DB=newdbhelper(getApplicationContext())代码>如果有用,请接受或投票。
public void onCreate(SQLiteDatabase db) {
data=db;
db.execSQL("CREATE TABLE " + TABLE_NAME + " ("
+ NAME + " TEXT,"
+ FATHER_NAME + " TEXT,"
+ MOTHER_NAME + " TEXT"
+ ");");
Log.d("DATABASE OPERATION", "TABLE CREATED");
}
DBHelper DB=new DBHelper(MainActivity.this);
ctxx = this;