基于安卓写一个简单的笔记app代码

以下是一个简单的安卓笔记app的代码示例，包含了添加笔记、编辑笔记、删除笔记和查看笔记的功能：

MainActivity.java

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

public class MainActivity extends AppCompatActivity {
    ListView notesListView;
    ArrayList<String> notesList;
    ArrayAdapter<String> adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        notesListView = findViewById(R.id.notes_list_view);
        notesList = new ArrayList<>();
        adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, notesList);
        notesListView.setAdapter(adapter);
        notesListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                editNoteDialog(i);
            }
        });
    }

    public void addNoteDialog(View view) {
        AddNoteDialog dialog = new AddNoteDialog();
        dialog.show(getSupportFragmentManager(), "addNoteDialog");
        dialog.setOnDialogCloseListener(new AddNoteDialog.OnDialogCloseListener() {
            @Override
            public void onDialogClose(String note) {
                notesList.add(note);
                adapter.notifyDataSetChanged();
            }
        });
    }

    public void editNoteDialog(final int position) {
        EditNoteDialog dialog = new EditNoteDialog();
        Bundle bundle = new Bundle();
        bundle.putString("note", notesList.get(position));
        dialog.setArguments(bundle);
        dialog.show(getSupportFragmentManager(), "editNoteDialog");
        dialog.setOnDialogCloseListener(new EditNoteDialog.OnDialogCloseListener() {
            @Override
            public void onDialogClose(String note) {
                notesList.set(position, note);
                adapter.notifyDataSetChanged();
            }
        });
    }

    public void deleteNoteDialog(View view) {
        DeleteNoteDialog dialog = new DeleteNoteDialog();
        dialog.show(getSupportFragmentManager(), "deleteNoteDialog");
        dialog.setOnDialogCloseListener(new DeleteNoteDialog.OnDialogCloseListener() {
            @Override
            public void onDialogClose(boolean delete) {
                if (delete) {
                    int position = notesListView.getCheckedItemPosition();
                    if (position != ListView.INVALID_POSITION) {
                        notesList.remove(position);
                        adapter.notifyDataSetChanged();
                        Toast.makeText(getApplicationContext(), "Note deleted", Toast.LENGTH_SHORT).show();
                    } else {
                        Toast.makeText(getApplicationContext(), "Please select a note to delete", Toast.LENGTH_SHORT).show();
                    }
                }
            }
        });
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/add_note_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Add Note"
        android:onClick="addNoteDialog"/>

    <Button
        android:id="@+id/edit_note_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Edit Note"
        android:layout_toRightOf="@id/add_note_button"
        android:layout_marginLeft="8dp"
        android:onClick="editNoteDialog"/>

    <Button
        android:id="@+id/delete_note_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Delete Note"
        android:layout_toRightOf="@id/edit_note_button"
        android:layout_marginLeft="8dp"
        android:onClick="deleteNoteDialog"/>

    <ListView
        android:id="@+id/notes_list_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@id/add_note_button"/>

</RelativeLayout>

AddNoteDialog.java

import android.app.Dialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatDialogFragment;

public class AddNoteDialog extends AppCompatDialogFragment {
    private EditText noteEditText;
    private Button addButton, cancelButton;
    private OnDialogCloseListener onDialogCloseListener;

    @NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        LayoutInflater inflater = getActivity().getLayoutInflater();
        View view = inflater.inflate(R.layout.dialog_add_note, null);
        noteEditText = view.findViewById(R.id.note_edit_text);
        addButton = view.findViewById(R.id.add_button);
        cancelButton = view.findViewById(R.id.cancel_button);
        addButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String note = noteEditText.getText().toString();
                if (!TextUtils.isEmpty(note)) {
                    onDialogCloseListener.onDialogClose(note);
                    dismiss();
                }
            }
        });
        cancelButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                dismiss();
            }
        });
        builder.setView(view);
        return builder.create();
    }

    public void setOnDialogCloseListener(OnDialogCloseListener onDialogCloseListener) {
        this.onDialogCloseListener = onDialogCloseListener;
    }

    public interface OnDialogCloseListener {
        void onDialogClose(String note);
    }
}

dialog_add_note.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="16dp">

    <EditText
        android:id="@+id/note_edit_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Enter note"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:gravity="end"
        android:layout_marginTop="16dp">

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

        <Button
            android:id="@+id/cancel_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Cancel"
            android:layout_marginLeft="16dp"/>

    </LinearLayout>

</LinearLayout>

EditNoteDialog.java

import android.app.Dialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatDialogFragment;

public class EditNoteDialog extends AppCompatDialogFragment {
    private EditText noteEditText;
    private Button saveButton, cancelButton;
    private OnDialogCloseListener onDialogCloseListener;

    @NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        LayoutInflater inflater = getActivity().getLayoutInflater();
        View view = inflater.inflate(R.layout.dialog_edit_note, null);
        noteEditText = view.findViewById(R.id.note_edit_text);
        saveButton = view.findViewById(R.id.save_button);
        cancelButton = view.findViewById(R.id.cancel_button);
        Bundle bundle = getArguments();
        if (bundle != null) {
            String note = bundle.getString("note");
            noteEditText.setText(note);
        }
        saveButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String note = noteEditText.getText().toString();
                if (!TextUtils.isEmpty(note)) {
                    onDialogCloseListener.onDialogClose(note);
                    dismiss();
                }
            }
        });
        cancelButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                dismiss();
            }
        });
        builder.setView(view);
        return builder.create();
    }

    public void setOnDialogCloseListener(OnDialogCloseListener onDialogCloseListener) {
        this.onDialogCloseListener = onDialogCloseListener;
    }

    public interface OnDialogCloseListener {
        void onDialogClose(String note);
    }
}

dialog_edit_note.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="16dp">

    <EditText
        android:id="@+id/note_edit_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Enter note"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:gravity="end"
        android:layout_marginTop="16dp">

        <Button
            android:id="@+id/save_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Save"/>

        <Button
            android:id="@+id/cancel_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Cancel"
            android:layout_marginLeft="16dp"/>

    </LinearLayout>

</LinearLayout>

DeleteNoteDialog.java

import android.app.Dialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatDialogFragment;

public class DeleteNoteDialog extends AppCompatDialogFragment {
    private Button deleteButton, cancelButton;
    private OnDialogCloseListener onDialogCloseListener;

    @NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        LayoutInflater inflater = getActivity().getLayoutInflater();
        View view = inflater.inflate(R.layout.dialog_delete_note, null);
        deleteButton = view.findViewById(R.id.delete_button);
        cancelButton = view.findViewById(R.id.cancel_button);
        deleteButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                onDialogCloseListener.onDialogClose(true);
                dismiss();
            }
        });
        cancelButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                dismiss();
            }
        });
        builder.setView(view);
        return builder.create();
    }

    public void setOnDialogCloseListener(OnDialogCloseListener onDialogCloseListener) {
        this.onDialogCloseListener = onDialogCloseListener;
    }

    public interface OnDialogCloseListener {
        void onDialogClose(boolean delete);
    }
}

dialog_delete_note.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="16dp">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Are you sure you want to delete this note?"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:gravity="end"
        android:layout_marginTop="16dp">

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

        <Button
            android:id="@+id/cancel_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Cancel"
            android:layout_marginLeft="16dp"/>

    </LinearLayout>

</LinearLayout>

注意：以上代码仅供参考，具体实现可能会因为不同的需求和场景而有所不同。