我正在创建一个应用程序，我已经创建了一个类设置email.java，我在其中保存了用户在sqlite数据库中输入的值。但是这个类无法加载，它说的是：
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.astrada/com.example.astrada.Setupemail}:
java.lang.InstantiationException: can't instantiate class com.example.astrada.Setupemail; no empty constructor
这是我的代码：
package com.example.astrada;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import com.example.astrada.R;
import android.app.Activity;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.DatabaseErrorHandler;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v4.widget.SimpleCursorAdapter;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class Setupemail extends Activity implements OnClickListener {
EditText editEmail, editPhon1, editPhon2, editphone3, editphone4, uname,
useraddress;
TextView TitleInfo;
Button save;
SqlOpenHelper mHelper;
Cursor mCursor;
SimpleCursorAdapter mAdapter;
private final Context context;
private SqlOpenHelper DBHelper;
private SQLiteDatabase mDb;
private static final String DATABASE_NAME = "databaseofuser.db";
private static final String DATABASE_TABLE = "usertable";
private static final int DATABASE_VERSION = 1;
public static final String EMAIL_COLUMN = "email";
public static final String PHONE1_COLUMN = "phon1";
public static final String PHONE2_COLUMN = "phon2";
public static final String PHONE3_COLUMN = "phon3";
public static final String PHONE4_COLUMN = "phon4";
public static final String UNAME_COLUMN = "phon4";
public static final String UADDR_COLUMN = "phon4";
private static final String DATABASE_CREATE = "create table "
+ DATABASE_TABLE + " (" + EMAIL_COLUMN + "," + PHONE1_COLUMN + ","
+ PHONE2_COLUMN + "," + PHONE3_COLUMN + "," + PHONE4_COLUMN + ","
+ UNAME_COLUMN + "," + UADDR_COLUMN + ");";
public Setupemail(Context ctx) {
this.context = ctx;
DBHelper = new SqlOpenHelper(context);
}
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.setupemail);
editEmail = (EditText) this.findViewById(R.id.editEmail);
editPhon1 = (EditText) this.findViewById(R.id.editPhon1);
editPhon2 = (EditText) this.findViewById(R.id.editPhon2);
editphone3 = (EditText) this.findViewById(R.id.editPhon3);
editphone4 = (EditText) this.findViewById(R.id.editPhon3);
uname = (EditText) this.findViewById(R.id.nameofuser);
useraddress = (EditText) this.findViewById(R.id.addressofuser);
editPhon1.append("+91");
editPhon2.append("+91");
editphone3.append("+91");
editphone4.append("+91");
mHelper = new SqlOpenHelper(this);
save = (Button) this.findViewById(R.id.btnSaveData);
save.setOnClickListener(this);
}
@Override
public void onClick(View v) {
String email, phon1, phon2, phon3, phon4;
boolean isEntryValid, isPhon1Valid, isPhone2Valid;
if (v == save) {
email = editEmail.getText().toString();
phon1 = editPhon1.getText().toString();
phon2 = editPhon2.getText().toString();
phon3 = editphone3.getText().toString();
phon4 = editphone4.getText().toString();
if (isEmailIdValid(email) && isPhoneValid(phon1)
&& isPhoneValid(phon2)) {
if (phon1.equals(phon2) || phon1.equals(phon3)
|| phon1.equals(phon4) || phon2.equals(phon3)
|| phon2.equals(phon4) || phon3.equals(phon4)) {
Toast.makeText(getApplicationContext(),
" Can't enter same numbers!!", Toast.LENGTH_LONG)
.show();
} else {
// /Saveinto DB
ContentValues cv = new ContentValues();
cv.put(EMAIL_COLUMN, editEmail.getText().toString());
cv.put(PHONE1_COLUMN, editPhon1.getText().toString());
cv.put(PHONE2_COLUMN, editPhon2.getText().toString());
cv.put(PHONE3_COLUMN, editphone3.getText().toString());
cv.put(UNAME_COLUMN, uname.getText().toString());
cv.put(UADDR_COLUMN, useraddress.getText().toString());
mDb.insert(DATABASE_TABLE, null, cv);
mCursor.requery();
mAdapter.notifyDataSetChanged();
Toast.makeText(getApplicationContext(), "Good Job!!",
Toast.LENGTH_LONG).show();
}
} else {
String x = "Invalid Entry!!\nProvide Information Properly..";
Toast.makeText(getApplicationContext(), x, Toast.LENGTH_LONG)
.show();
editEmail.setText("");
}
}
// TODO Auto-generated method stub
}
private boolean isPhoneValid(String phon) {
final Pattern pattern = Pattern.compile(
"^([\\+](91))?([7-9]{1})([0-9]{9})$", Pattern.CASE_INSENSITIVE
| Pattern.MULTILINE);
Matcher match = pattern.matcher(phon);
if (match.matches()) {
return true;
} else {
return false;
}
}
private boolean isEmailIdValid(String Email) {
boolean isValid = false;
String expression = "^[\\w\\.-]+@([\\w\\-]+\\.)+[A-Z]{2,4}$";
CharSequence inputStr = Email;
Pattern pattern = Pattern.compile(expression, Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern.matcher(inputStr);
if (matcher.matches()) {
isValid = true;
}
return isValid;
}
public class SqlOpenHelper extends SQLiteOpenHelper {
public SqlOpenHelper() {
super(context, null, null, 0);
}
public SqlOpenHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION, null);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(DATABASE_CREATE);
}
public SQLiteOpenHelper open() throws SQLException {
mDb = DBHelper.getWritableDatabase();
return this;
}
public void colse() {
DBHelper.close();
}
public long insertContact(String email, String phon1, String phon2,
String phon3, String phon4, String name, String address) {
ContentValues initialValues = new ContentValues();
initialValues.put(EMAIL_COLUMN, email);
initialValues.put(PHONE1_COLUMN, phon1);
initialValues.put(PHONE2_COLUMN, phon2);
initialValues.put(PHONE3_COLUMN, phon3);
initialValues.put(PHONE4_COLUMN, phon4);
initialValues.put(UNAME_COLUMN, name);
initialValues.put(UADDR_COLUMN, address);
return mDb.insert(DATABASE_TABLE, null, initialValues);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w("TaskDBAdapter", "Upgrading from version" + oldVersion
+ " to " + newVersion + ", which will destroy all old data");
// Upgrade the existing database to conform to the new
// version. Multiple previous versions can be handled by
// comparing oldVersion and newVersion values.
// The simplest case is to drop the old table and create a new one.
db.execSQL("DROP TABLE IF IT EXISTS " + DATABASE_TABLE);
// Create a new one.
onCreate(db);
}
}
}
答案 0 :(得分：3)
活动不应该有构造函数！所有这些都应该在生命周期回调中完成。将内容从ctor移到onCreate（）并删除ctor：
public Setupemail(Context ctx) {
this.context = ctx;
DBHelper = new SqlOpenHelper(context);
}
答案 1 :(得分：2)
放弃这个：
public Setupemail(Context ctx) {
this.context = ctx;
DBHelper = new SqlOpenHelper(context);
}
并删除context字段。 Setupemail类继承自Activity，它是Context本身的子类。如果您想引用Context，可以在内部类中使用getBaseContext，甚至可以在Setupemail类中省略它。
答案 2 :(得分：-1)
public Setupmail()
{
}