宝剑锋从磨砺出，梅花香自苦寒来。这篇文章主要讲述将用户输入编辑文本与SQLite数据库Android Java进行比较相关的知识，希望能为你提供帮助。
您好我正在制作一个教师助理应用程序，该应用程序使用SQLite数据库，并允许教师通过添加更新和删除学生参加考勤，每次添加新学生时生成学生ID，现在这里是如何显示错误消息的事情，如果教师的输入与数据库中的学生ID不匹配，而不是让我的应用程序崩溃。
StudentOperations
package com.appcreator.isa.theteacherassistantapp.Database;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import com.appcreator.isa.theteacherassistantapp.Model.Student;
import java.util.ArrayList;
import java.util.List;
public class StudentOperations
{
public static final String LOGTAG = "STD_MNGMNT_SYS";
SQLiteOpenHelper dbhandler;
SQLiteDatabase database;
private static final String[] allColumns = {
StudentDatabaseHandler.COLUMN_SID,
StudentDatabaseHandler.COLUMN_EID,
StudentDatabaseHandler.COLUMN_FIRST_NAME,
StudentDatabaseHandler.COLUMN_LAST_NAME,
StudentDatabaseHandler.COLUMN_STUDY,
StudentDatabaseHandler.COLUMN_ATTENDANCE};
public StudentOperations(Context context)
{
dbhandler = new StudentDatabaseHandler(context);
}public void open()
{
Log.i(LOGTAG,"Database Opened");
database = dbhandler.getWritableDatabase();
}
public void close()
{
Log.i(LOGTAG, "Database Closed");
dbhandler.close();
}
public Student addStudent(Student Student)
{
ContentValues values= new ContentValues();
values.put(StudentDatabaseHandler.COLUMN_EID, Student.getEnrlomentID());
values.put(StudentDatabaseHandler.COLUMN_FIRST_NAME,Student.getFirstname());
values.put(StudentDatabaseHandler.COLUMN_LAST_NAME,Student.getLastname());
values.put(StudentDatabaseHandler.COLUMN_STUDY, Student.getStudy());
values.put(StudentDatabaseHandler.COLUMN_ATTENDANCE, Student.getAttendance());
long insertSID = database.insert(StudentDatabaseHandler.TABLE_STUDENTS,null,values);
Student.setStudentID(insertSID);
return Student;
}// Getting single Student
public Student getStudent(long id)
{
Cursor cursor = database.query(StudentDatabaseHandler.TABLE_STUDENTS,allColumns,StudentDatabaseHandler.COLUMN_SID + "=?",new String[]{String.valueOf(id)},null,null, null, null);
if (cursor != null)
cursor.moveToFirst();
Student e = new Student(Long.parseLong(cursor.getString(0)),cursor.getString(1),cursor.getString(2),cursor.getString(3),cursor.getString(4),cursor.getString(5));
// return Student
return e;
}public List<
Student>
getAllStudents()
{
Cursor cursor = database.query(StudentDatabaseHandler.TABLE_STUDENTS,allColumns,null,null,null, null, null);
List<
Student>
students = new ArrayList<
>
();
if(cursor.getCount() >
0)
{
while(cursor.moveToNext())
{
Student student = new Student();
student.setStudentID(cursor.getLong(cursor.getColumnIndex(StudentDatabaseHandler.COLUMN_SID)));
student.setEnrlomentID(cursor.getString(cursor.getColumnIndex(StudentDatabaseHandler.COLUMN_EID)));
student.setFirstname(cursor.getString(cursor.getColumnIndex(StudentDatabaseHandler.COLUMN_FIRST_NAME)));
student.setLastname(cursor.getString(cursor.getColumnIndex(StudentDatabaseHandler.COLUMN_LAST_NAME)));
student.setStudy(cursor.getString(cursor.getColumnIndex(StudentDatabaseHandler.COLUMN_STUDY)));
student.setAttendance(cursor.getString(cursor.getColumnIndex(StudentDatabaseHandler.COLUMN_ATTENDANCE)));
students.add(student);
}
}
// return All Students
return students;
}// Updating Student
public int updateStudent(Student student)
{
ContentValues values = new ContentValues();
values.put(StudentDatabaseHandler.COLUMN_EID, student.getEnrlomentID());
values.put(StudentDatabaseHandler.COLUMN_FIRST_NAME, student.getFirstname());
values.put(StudentDatabaseHandler.COLUMN_LAST_NAME, student.getLastname());
values.put(StudentDatabaseHandler.COLUMN_STUDY, student.getStudy());
values.put(StudentDatabaseHandler.COLUMN_ATTENDANCE, student.getAttendance());
// updating row
return database.update(StudentDatabaseHandler.TABLE_STUDENTS, values,
StudentDatabaseHandler.COLUMN_SID + "=?",new String[] { String.valueOf(student.getStudentID())});
}// Deleting Student
public void removeStudent(Student student)
{
database.delete(StudentDatabaseHandler.TABLE_STUDENTS, StudentDatabaseHandler.COLUMN_SID + "=" + student.getStudentID(), null);
}}
主要活动
package com.appcreator.isa.theteacherassistantapp;
import android.content.DialogInterface;
import android.content.Intent;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.appcreator.isa.theteacherassistantapp.Database.StudentDatabaseHandler;
import com.appcreator.isa.theteacherassistantapp.Database.StudentOperations;
import com.appcreator.isa.theteacherassistantapp.Model.Student;
public class MainActivity extends AppCompatActivity
{private Button addStudentButton;
private Button editStudentButton;
private Button deleteStudentButton;
private StudentOperations studentOps;
private static final String EXTRA_STUDENT_ID = "TEMP";
private static final String EXTRA_ADD_UPDATE = "TEMP";
@Override
protected void onCreate(Bundle savedInstanceState)
{super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
addStudentButton = (Button) findViewById(R.id.button_add_student);
editStudentButton = (Button) findViewById(R.id.button_edit_student);
deleteStudentButton = (Button) findViewById(R.id.button_delete_student);
addStudentButton.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v)
{
Intent i = new Intent(MainActivity.this,AddUpdateStudent.class);
i.putExtra(EXTRA_ADD_UPDATE, "Add");
startActivity(i);
}
});
editStudentButton.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v) {
getStudentIDAndUpdateStudent();
}
});
deleteStudentButton.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v) {
getStudentIDAndRemoveStudent();
}
});
}public void getStudentIDAndUpdateStudent()
{LayoutInflater li = LayoutInflater.from(this);
View getStudentIdView = li.inflate(R.layout.dialog_get_student_id, null);
AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);
// set dialog_get_student_id.xml to alertdialog builder
alertDialogBuilder.setView(getStudentIdView);
final EditText userInput = (EditText) getStudentIdView.findViewById(R.id.editTextDialogUserInput);
// set dialog message
alertDialogBuilder
.setCancelable(false)
.setPositiveButton("OK",new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int id)
{
if (userInput.getText().toString().trim().length() >
0)
{
// get user input and set it to result
// edit text
Intent i = new Intent(MainActivity.this,AddUpdateStudent.class);
i.putExtra(EXTRA_ADD_UPDATE, "Update");
i.putExtra(EXTRA_STUDENT_ID, Long.parseLong(userInput.getText().toString()));
startActivity(i);
}
else
{
Toast.makeText(MainActivity.this, "Input is invalid", Toast.LENGTH_SHORT).show();
}
}
}).create()
.show();
}public void getStudentIDAndRemoveStudent(){LayoutInflater li = LayoutInflater.from(this);
View getStudentIdView = li.inflate(R.layout.dialog_get_student_id, null);
AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);
// set dialog_get_student_id.xml to alertdialog builder
alertDialogBuilder.setView(getStudentIdView);
final EditText userInput = (EditText) getStudentIdView.findViewById(R.id.editTextDialogUserInput);
// set dialog message
alertDialogBuilder
.setCancelable(false)
.setPositiveButton("OK",new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int id)
{
if (userInput.getText().toString().trim().length() >
0)
{
// get user input and set it to result
// edit text
//studentOps = new StudentOperations(MainActivity.this);
disabled because placing it here causes error
studentOps.removeStudent(studentOps.getStudent(Long.parseLong(userInput.getText().toString())));
Toast.makeText(MainActivity.this, "Student has been removed successfully", Toast.LENGTH_SHORT).show();
}
else
{
Toast.makeText(MainActivity.this, "Input is invalid", Toast.LENGTH_SHORT).show();
}
}
}).create()
.show();
}
@Override
protected void onResume()
{
super.onResume();
studentOps = new StudentOperations(MainActivity.this);
studentOps.open();
}@Override
protected void onPause()
{
super.onPause();
studentOps.close();
}
}
logcat的
10-17 03:42:09.750 11105-11105/com.appcreator.isa.theteacherassistantapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.appcreator.isa.theteacherassistantapp, PID: 11105
android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
at android.database.AbstractCursor.checkPosition(AbstractCursor.java:460)
at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:136)
at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:50)
at com.appcreator.isa.theteacherassistantapp.Database.StudentOperations.getStudent(StudentOperations.java:71)
at com.appcreator.isa.theteacherassistantapp.MainActivity$5.onClick(MainActivity.java:144)
at android.support.v7.app.AlertController$ButtonHandler.handleMessage(AlertController.java:167)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:241)
at android.app.ActivityThread.main(ActivityThread.java:6274)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
更新了主要活动
package com.appcreator.isa.theteacherassistantapp;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.Cursor;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.appcreator.isa.theteacherassistantapp.Database.StudentDatabaseHandler;
import com.appcreator.isa.theteacherassistantapp.Database.StudentOperations;
import com.appcreator.isa.theteacherassistantapp.Model.Student;
public class MainActivity extends AppCompatActivity
{private Button addStudentButton;
private Button editStudentButton;
private Button deleteStudentButton;
private StudentOperations studentOps;
private static final String EXTRA_STUDENT_ID = "TEMP";
private static final String EXTRA_ADD_UPDATE = "TEMP";
private static final String TAG = "Student Exits";
@Override
protected void onCreate(Bundle savedInstanceState)
{super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
addStudentButton = (Button) findViewById(R.id.button_add_student);
editStudentButton = (Button) findViewById(R.id.button_edit_student);
deleteStudentButton = (Button) findViewById(R.id.button_delete_student);
addStudentButton.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v)
{
Intent i = new Intent(MainActivity.this,AddUpdateStudent.class);
i.putExtra(EXTRA_ADD_UPDATE, "Add");
startActivity(i);
}
});
editStudentButton.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v) {
getStudentIDAndUpdateStudent();
}
});
deleteStudentButton.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v) {
getStudentIDAndRemoveStudent();
}
});
}public boolean check_existence(String stud_id)
{
SQLiteOpenHelper db = new StudentDatabaseHandler(this);
SQLiteDatabase database = db.getWritableDatabase();
String select = "SELECT * FROM students WHERE studentID =" + stud_id;
Cursor c = database.rawQuery(select, null);
if (c.moveToFirst())
{
Log.d(TAG,"Student Exists");
return true;
}if(c!=null)
{
c.close();
}
database.close();
return false;
}public void getStudentIDAndUpdateStudent()
{LayoutInflater li = LayoutInflater.from(this);
final View getStudentIdView = li.inflate(R.layout.dialog_get_student_id, null);
AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);
// set dialog_get_student_id.xml to alertdialog builder
alertDialogBuilder.setView(getStudentIdView);
final EditText userInput = (EditText) getStudentIdView.findViewById(R.id.editTextDialogUserInput);
// set dialog message
alertDialogBuilder
.setCancelable(false)
.setPositiveButton("OK",new DialogInterface.OnClickListener()
{
public void onClick(DialogInterface dialog,int id)
{
if (userInput.getText().toString().isEmpty())
{
Toast.makeText(MainActivity.this, "Input is invalid", Toast.LENGTH_SHORT).show();
}
else
{
// get user input and set it to result
// edit text
if (check_existence(userInput.getText().toString()) == true)
{
Intent i = new Intent(MainActivity.this,AddUpdateStudent.class);
i.putExtra(EXTRA_ADD_UPDATE, "Update");
i.putExtra(EXTRA_STUDENT_ID, Long.parseLong(userInput.getText().toString()));
startActivity(i);
}
else
{
Toast.makeText(MainActivity.this, "Input is invalid", Toast.LENGTH_SHORT).show();
}}
}
}).create()
.show();
}public void getStudentIDAndRemoveStudent()
{LayoutInflater li = LayoutInflater.from(this);
View getStudentIdView = li.inflate(R.layout.dialog_get_student_id, null);
AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);
// set dialog_get_student_id.xml to alertdialog builder
alertDialogBuilder.setView(getStudentIdView);
final EditText userInput = (EditText) getStudentIdView.findViewById(R.id.editTextDialogUserInput);
// set dialog message
alertDialogBuilder
.setCancelable(false)
.setPositiveButton("OK",new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int id)
{
if (userInput.getText().toString().isEmpty())
{
Toast.makeText(MainActivity.this, "Invalid Input", Toast.LENGTH_SHORT).show();
}
else
{
if(check_existence(userInput.getText().toString()) == true)
{
// get user input and set it to result
// edit text
//studentOps = new StudentOperations(MainActivity.this);
disabled because placing it here causes error
studentOps.removeStudent(studentOps.getStudent(Long.parseLong(userInput.getText().toString())));
Toast.makeText(MainActivity.this, "Student has been removed successfully", Toast.LENGTH_SHORT).show();
}
else
{
Toast.makeText(MainActivity.this, "Invalid Input" , Toast.LENGTH_SHORT).show();
}
}
}
}).create()
.show();
}@Override
protected void onResume()
{
super.onResume();
studentOps = new StudentOperations(MainActivity.this);
studentOps.open();
}@Override
protected void onPause()
{
super.onPause();
studentOps.close();
}
}
答案您可以使用
boolean数据类型创建一个新方法，如果返回false，您可能希望通过Toast或类似的方式将其显示给用户。【将用户输入编辑文本与SQLite数据库Android Java进行比较】在代码中可能看起来像这样：
public boolean check_existence(String stud_id) {SQLiteDatabase db = this.getWritableDatabase();
String select = "SELECT * FROM table_name WHERE column_name ='" + stud_id;
Cursor c = db.rawQuery(select, null);
if (c.moveToFirst()) {Log.d(TAG,"User exits");
return true;
}if(c!=null) {c.close();
}
db.close();
return false;
}
您现在可以调用该方法，如果它返回
false，您可以使用Toast显示您想要的内容。推荐阅读
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