Android Studio 日期选择器 及日期对话框
activity_main.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="match_parent"
    android:orientation="vertical"
    >

    <TextView
        android:text="hello world!"
        android:layout_gravity="center"
        android:id="@+id/tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

    <DatePicker
        android:layout_marginTop="50dp"
        android:layout_gravity="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

    <Button
        android:layout_gravity="center"
        android:layout_marginTop="10dp"
        android:text="按钮"
        android:id="@+id/bt"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

</LinearLayout>

MainActivity.java

package com.easybooks.myapplication;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

import android.app.DatePickerDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.DatePicker;
import android.widget.TextView;

import java.util.Calendar;

public class MainActivity extends AppCompatActivity {

    private TextView textView;
    private Button button;
    private String decs;

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

        textView = findViewById(R.id.tv);
        button = findViewById(R.id.bt);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Calendar calendar = Calendar.getInstance();

                DatePickerDialog dialog = new DatePickerDialog(MainActivity.this,
                        new DatePickerDialog.OnDateSetListener() {
                            @Override
                            public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {

                                 decs = String.format("%d %d %d", year, month, dayOfMonth);

                            }
                        },
                        calendar.get(Calendar.YEAR),
                        calendar.get(Calendar.MONTH),
                        calendar.get(Calendar.DAY_OF_MONTH));

                dialog.show();
                textView.setText(decs);

            }
        });


        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("hello world");
        builder.setMessage("hello world");
        builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {

            }
        });

        AlertDialog alter = builder.create();
        alter.show();


    }
}