package com.example.todoapp;

import android.graphics.Paint;
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.TextView;

import androidx.appcompat.app.AppCompatActivity;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    EditText editTextTask;
    Button buttonAdd;
    ListView listView;

    ArrayList<String> tasks;
    ArrayAdapter<String> adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        editTextTask = findViewById(R.id.editTextTask);
        buttonAdd = findViewById(R.id.buttonAdd);
        listView = findViewById(R.id.listView);

        tasks = new ArrayList<>();

        adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, tasks);

        listView.setAdapter(adapter);

        buttonAdd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String text = editTextTask.getText().toString().trim();

                if (!text.isEmpty()) {
                    tasks.add(text);
                    adapter.notifyDataSetChanged();
                    editTextTask.setText("");
                }
            }
        });

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                TextView textView = (TextView) view;

                textView.setPaintFlags(
                        textView.getPaintFlags() | Paint.STRIKE_THRU_TEXT_FLAG
                );

                String task = tasks.get(position);
                tasks.remove(position);
                tasks.add(task);

                adapter.notifyDataSetChanged();
            }
        });
    }
}

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

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <EditText
            android:id="@+id/editTextTask"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="Wpisz zadanie"/>

        <Button
            android:id="@+id/buttonAdd"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Dodaj"/>
    </LinearLayout>

    <ListView
        android:id="@+id/listView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:dividerHeight="8dp"/>
</LinearLayout>