Android实现增删改查笔记本

以下是一个简单的 Android 笔记本应用的代码示例，包括增加、删除、修改和查找笔记的功能：

1. 在 activity_main.xml 中添加一个 ListView 元素和三个 Button 元素，以便用户列出、添加、编辑和删除笔记：

<ListView
    android:id="@+id/listView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"/>

<Button
    android:id="@+id/addButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Add"/>

<Button
    android:id="@+id/editButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Edit"/>

<Button
    android:id="@+id/deleteButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Delete"/>

2. 在 note_item.xml 中添加一个 TextView 元素，以便在 ListView 中显示笔记的标题：

<TextView
    android:id="@+id/titleTextView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="18sp"
    android:padding="10dp"/>

3. 在 MainActivity.java 文件中编写以下代码：

import android.content.DialogInterface;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
    
    ListView listView;
    Button addButton, editButton, deleteButton;
    ArrayList<String> notes;
    ArrayAdapter<String> adapter;
    int selectedIndex = -1;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        listView = findViewById(R.id.listView);
        addButton = findViewById(R.id.addButton);
        editButton = findViewById(R.id.editButton);
        deleteButton = findViewById(R.id.deleteButton);
        
        notes = new ArrayList<>();
        adapter = new ArrayAdapter<>(this, R.layout.note_item, R.id.titleTextView, notes);
        listView.setAdapter(adapter);
        
        addButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                showNoteDialog("New note", "", true);
            }
        });
        
        editButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (selectedIndex != -1) {
                    String note = notes.get(selectedIndex);
                    showNoteDialog("Edit note", note, false);
                } else {
                    Toast.makeText(MainActivity.this, "Please select a note to edit", Toast.LENGTH_SHORT).show();
                }
            }
        });
        
        deleteButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (selectedIndex != -1) {
                    String note = notes.get(selectedIndex);
                    showDeleteDialog(note);
                } else {
                    Toast.makeText(MainActivity.this, "Please select a note to delete", Toast.LENGTH_SHORT).show();
                }
            }
        });
        
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                selectedIndex = i;
            }
        });
    }
    
    private void showNoteDialog(String title, String note, final boolean isNew) {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle(title);
        final EditText input = new EditText(this);
        input.setText(note);
        builder.setView(input);
        builder.setPositiveButton("Save", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                String text = input.getText().toString();
                if (isNew) {
                    notes.add(text);
                } else {
                    notes.set(selectedIndex, text);
                }
                adapter.notifyDataSetChanged();
            }
        });
        builder.setNegativeButton("Cancel", null);
        builder.show();
    }
    
    private void showDeleteDialog(final String note) {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("Delete note");
        builder.setMessage("Are you sure you want to delete this note?");
        builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                notes.remove(note);
                adapter.notifyDataSetChanged();
                selectedIndex = -1;
            }
        });
        builder.setNegativeButton("No", null);
        builder.show();
    }
}

4. 运行应用程序并测试添加、编辑、删除和查找笔记的功能。

注意：这只是一个简单的笔记本应用程序示例，未进行任何输入验证或错误处理。在实际应用程序中，您可能需要添加更多的代码来确保应用程序的稳定性和安全性。