In recent days, I have made a notepad applet with my current Android development knowledge. I would like to share the development process here, hoping to help beginners like me.
The development tool is Android studio, the background language is java, and the database used is Android SQLite database. The functions and renderings are as follows:
Main interface, long press to delete:
Click the plus sign to add:
Click View on the main page, this page includes modification and deletion functions:
Main technologies used: database storage used for data storage. My previous blog talked about the basic operation of Android SQLite; ListView component is used for data display, and intent technology is used for data transmission, with the help of intent for jump between pages; click a line on the homepage, pass its id to the viewing page through intent, and read data from the database according to id for display , deletion is also a database operation based on id.
The entire project file has been synchronized to GitHub. Please take https://github.com/liuleliu/textbook
Here is the main code:
Database auxiliary class:
package com.example.myapplication;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DataBaseHelp extends SQLiteOpenHelper{
private static final String DATABASENAME ="tip1";//Database name
private static final int DATABASEVERSION =1;//Database version
private static final String TABLENAME="tip1";//Table name
public DataBaseHelp(Context context)//Definition construction
{
super(context,DATABASENAME,null,DATABASEVERSION); //Call parent class construction
}
public void onCreate(SQLiteDatabase db)
{
String sql="CREATE TABLE "+TABLENAME+"("+
"id INTEGER PRIMARY KEY AUTOINCREMENT,"+ //Set auto grow columns
"name VARCHAR(50) NOT NULL,"+
"text VARCHAR(50) NOT NULL)";
db.execSQL(sql); //Execute sql statement
}
public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion)
{
String sql="DROP TABLE IF EXISTS "+TABLENAME;
db.execSQL(sql);
this.onCreate(db);//Create table
}
}
Operation class
package com.example.myapplication;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class OperateTable {
private static final String TABLENAME ="tip1";
private SQLiteDatabase db=null;
public OperateTable(SQLiteDatabase db)
{
this.db=db;
}
public void insert(String name,String text)
{
String sql="INSERT INTO "+TABLENAME+" (name,text) VALUES ('"+name+"','"+text+"')";
this.db.execSQL(sql);
}
public void delete(String id)
{
String sql="DELETE FROM "+TABLENAME+" WHERE id='"+id+"'";
this.db.execSQL(sql);
}
public void updata(String id,String name,String text)
{
String sql="UPDATE "+TABLENAME+" SET name ='"+name+"',text='"+text+"' WHERE id='"+id+"'";
this.db.execSQL(sql);
}
public List<Map<String,Object>> getdata()
{List<Map<String,Object>>list=new ArrayList<Map<String,Object>>();
Map<String,Object> map=new HashMap<String,Object>();
String sql="SELECT id,name,text FROM "+TABLENAME;
Cursor result =this.db.rawQuery(sql,null);
for(result.moveToFirst();!result.isAfterLast();result.moveToNext())
{
map=new HashMap<String,Object>();
map.put("id",result.getInt(0));
map.put("tt",result.getString(1));
list.add(map);
}
return list;}
public tip t(String id)
{
tip t=new tip();
String sql="SELECT name,text FROM "+TABLENAME+" WHERE id ='"+id+"'";
Cursor result =this.db.rawQuery(sql,null);
result.moveToFirst();
t.setName(result.getString(0));
t.setText(result.getString(1));
return t;
}
}
The data display and interaction of the home page involve the use of ListView
The update of data needs to overload the onResume() function to implement
Layout:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/linearLayout2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<com.google.android.material.floatingactionbutton.FloatingActionButton
android:id="@+id/add"
android:layout_width="59dp"
android:layout_height="57dp"
android:layout_marginEnd="28dp"
android:clickable="true"
app:backgroundTint="#2894FF"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.807"
app:srcCompat="@android:drawable/ic_input_add" />
<ListView
android:id="@+id/vi"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:layout_marginBottom="389dp"
app:layout_constraintBottom_toTopOf="@+id/add"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.034"></ListView>
</androidx.constraintlayout.widget.ConstraintLayout>
Here is the layout of each line
<TextView
android:id="@+id/id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="39dp"
android:layout_marginBottom="24dp"
android:text="TextView"
android:textColor="#00000000"
app:layout_constraintBottom_toBottomOf="@+id/pic"
app:layout_constraintStart_toStartOf="parent" />
<ImageView
android:id="@+id/pic"
android:layout_width="142dp"
android:layout_height="101dp"
android:src="@mipmap/ic_launcher_round"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
Then it is the operation in the main class, assigning values to the ListView, setting interaction events (stand-alone, long press)
package com.example.myapplication;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class MainActivity extends AppCompatActivity {
private OperateTable mytable =null;
private SQLiteOpenHelper helper=null;
private FloatingActionButton add=null;
private String info=null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
helper=new DataBaseHelp(this);
helper.getWritableDatabase();
MainActivity.this.mytable=new OperateTable(MainActivity.this.helper.getWritableDatabase());
SimpleAdapter adapter = new SimpleAdapter(this,this.mytable.getdata(), R.layout.activity_main
, new String[]{"id","tt"},
new int[]{R.id.id,R.id.tt});
ListView listView=(ListView)findViewById(R.id.vi);
add=(FloatingActionButton)findViewById(R.id.add);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new OnItemClick());//Register Click to listen
listView.setOnItemLongClickListener(new OnItemLongClick());//Registrar press monitor
add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent it=new Intent(MainActivity.this,add.class);
MainActivity.this.startActivity(it);
}
});
}
private class OnItemClick implements AdapterView.OnItemClickListener
{ public void onItemClick(AdapterView<?>arg0, View arg1, int arg2, long arg3){
ListView list = (ListView) findViewById(R.id.vi);
HashMap<String,Object> map=(HashMap<String,Object>)list.getItemAtPosition(arg2);
info=map.get("id").toString();
Intent it=new Intent(MainActivity.this,receive.class);
it.putExtra("info",info);//Transfer data to receive
MainActivity.this.startActivity(it);
}
}
private class OnItemLongClick implements AdapterView.OnItemLongClickListener
{
public boolean onItemLongClick(AdapterView<?>arg0, View arg1, int arg2, long arg3){
ListView list = (ListView) findViewById(R.id.vi);
HashMap<String,Object> map=(HashMap<String,Object>)list.getItemAtPosition(arg2);
String name;
info=map.get("id").toString();
name=map.get("tt").toString();
AlertDialog myAlertDialog = new AlertDialog.Builder(MainActivity.this)
.setTitle("confirm" )
.setMessage("OK to delete“"+name+""Do you?" )
.setPositiveButton("yes" , new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
mytable.delete(info);
Toast.makeText(getApplicationContext(),"Delete successful",Toast.LENGTH_SHORT).show();
onResume();
}
})
.setNegativeButton("no" , null)
.show();
return true;
}
}
//Every time I go back to the home page, it will be executed to update the data
public void onResume() {
super.onResume(); // Always call the superclass method first
SimpleAdapter adapter = new SimpleAdapter(this,MainActivity.this.mytable.getdata(), R.layout.activity_main
, new String[]{"id","tt"},
new int[]{R.id.id,R.id.tt});
ListView listView=(ListView)findViewById(R.id.vi);
add=(FloatingActionButton)findViewById(R.id.add);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new OnItemClick());
add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent it=new Intent(MainActivity.this,add.class);
MainActivity.this.startActivity(it);
}
});
}
}
It is easy to add, that is to get data and call database operation to save data
layout
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/linearLayout3"
android:layout_width="match_parent"
android:layout_height="match_parent">
<EditText
android:id="@+id/aname"
android:layout_width="283dp"
android:layout_height="0dp"
android:layout_marginStart="60dp"
android:layout_marginTop="26dp"
android:layout_marginBottom="461dp"
android:hint="Title"
android:maxLines="1"
android:maxLength="25"
app:layout_constraintBottom_toTopOf="@+id/save"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"></EditText>
<EditText
android:id="@+id/atext"
android:layout_width="335dp"
android:layout_height="426dp"
android:layout_marginStart="43dp"
android:layout_marginBottom="84dp"
android:hint="content"
android:minLines="5"
android:gravity="top"
android:background="@null"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/aname"></EditText>
<Button
android:id="@+id/save"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="17dp"
android:text="Preservation"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="@+id/atext"
app:layout_constraintTop_toBottomOf="@+id/aname" />
</androidx.constraintlayout.widget.ConstraintLayout>
Activity class
package com.example.myapplication;
import androidx.appcompat.app.AppCompatActivity;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class add extends AppCompatActivity {
private OperateTable mytable =null;
private SQLiteOpenHelper helper=null;
private EditText name=null;
private EditText text=null;
private Button save=null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.add);
this.name=(EditText)super.findViewById(R.id.aname);
this.text=(EditText)super.findViewById(R.id.atext);
Button save=( Button) super.findViewById(R.id.save);
helper=new DataBaseHelp(this);
helper.getWritableDatabase();
mytable=new OperateTable(helper.getWritableDatabase());
save.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if(name.getText().toString().equals("")){Toast.makeText(getApplicationContext(),"Please enter a title",Toast.LENGTH_SHORT).show();}
else{ mytable.insert(name.getText().toString(),text.getText().toString());//Save data
Toast.makeText(getApplicationContext(),"Save successfully",Toast.LENGTH_SHORT).show();
add.this.finish();//End the current Activity and return to the main page}
}
});
}
}
View the page, receive the id from the home page through intent, obtain the corresponding data and display
Layout:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/linearLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<EditText
android:id="@+id/name"
android:layout_width="303dp"
android:layout_height="46dp"
android:layout_marginStart="60dp"
android:layout_marginTop="36dp"
android:layout_marginBottom="14dp"
android:hint="Title"
android:text="TextView"
android:maxLength="25"
app:layout_constraintBottom_toTopOf="@+id/divider"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<EditText
android:id="@+id/text"
android:layout_width="308dp"
android:layout_height="400dp"
android:layout_marginStart="52dp"
android:layout_marginEnd="52dp"
android:layout_marginBottom="63dp"
android:background="@null"
android:gravity="top"
android:hint="content"
android:minLines="5"
android:text="TextView"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/name"
app:layout_constraintVertical_bias="1.0" />
<View
android:id="@+id/divider"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginStart="1dp"
android:layout_marginTop="83dp"
android:layout_marginEnd="1dp"
android:layout_marginBottom="433dp"
android:background="?android:attr/listDivider"
app:layout_constraintBottom_toTopOf="@+id/delete"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/delete"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="29dp"
android:layout_marginBottom="6dp"
android:text="delete"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="@+id/divider" />
<Button
android:id="@+id/edit"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="29dp"
android:layout_marginBottom="7dp"
android:text="Save changes"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
Activities
package com.example.myapplication;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import android.content.DialogInterface;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.content.Intent;
import android.widget.Toast;
public class receive extends AppCompatActivity {
private EditText name=null;
private EditText text=null;
private Button delete=null;
private Button edit=null;
private OperateTable mytable =null;
private SQLiteOpenHelper helper=null;
private String info=null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.receive);
this.name=(EditText)super.findViewById(R.id.name);
this.text=(EditText)super.findViewById(R.id.text);
this.delete=(Button)super.findViewById(R.id.delete);
this.edit=(Button)super.findViewById(R.id.edit);
Intent it=super.getIntent();
info=it.getStringExtra("info");//Get id of homepage delivery
helper=new DataBaseHelp(this);
helper.getWritableDatabase();
mytable=new OperateTable(helper.getWritableDatabase());
tip t=mytable.t(info);
name.setText(t.getName());
text.setText(t.getText());
delete.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AlertDialog myAlertDialog = new AlertDialog.Builder(receive.this)
.setTitle("confirm" )
.setMessage("OK to delete“"+name.getText()+""Do you?" )
.setPositiveButton("yes" , new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
mytable.delete(info);
Toast.makeText(getApplicationContext(),"Delete successful",Toast.LENGTH_SHORT).show();
receive.this.finish();
}
})
.setNegativeButton("no" , null)
.show();
}
});
edit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mytable.updata(info,name.getText().toString(),text.getText().toString());
Toast.makeText(getApplicationContext(),"Modified success",Toast.LENGTH_SHORT).show();
receive.this.finish();
}
});
}
}