参考视频：Android Development for Beginners - Full Course

一、MainActivity.java

package com.example.challenge_1;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

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

    public void Register(View view)
    {
        TextView textView_display = findViewById(R.id.TextView_Display);
        EditText edtText_uname = findViewById(R.id.EdtText_Username);
        EditText editText_pwd = findViewById(R.id.EdtText_Password);

        textView_display.setText("Uname: " + edtText_uname.getText().toString() + ", Pwd: " + editText_pwd.getText().toString());
    }
}

一、activity_main.xml

<?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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

<!-- Username -->
    <EditText
        android:id="@+id/EdtText_Username"
        android:layout_width="300dp"
        android:layout_height="100dp"
        android:layout_marginTop="100dp"
        android:ems="10"
        android:hint="Username"
        android:inputType="text"
        android:textSize="48dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
    />

<!-- Password -->
    <EditText
        android:id="@+id/EdtText_Password"
        android:layout_width="300dp"
        android:layout_height="100dp"
        android:layout_marginTop="200dp"
        android:ems="10"
        android:hint="Password"
        android:inputType="textPassword"
        android:textSize="48dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
    />

<!-- Register BTN -->
    <Button
        android:id="@+id/Btn_Register"
        android:layout_width="200dp"
        android:layout_height="100dp"
        android:layout_marginTop="400dp"
        android:text="Register"
        android:textSize="48dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:onClick="Register"
    />

<!-- TextView -->
    <TextView
        android:id="@+id/TextView_Display"
        android:layout_width="500dp"
        android:layout_height="100dp"
        android:layout_marginTop="600dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
    />

</androidx.constraintlayout.widget.ConstraintLayout>