Android Kotlin - Exemplo Simples

Links relacionados: Programação para Dispositivos Móveis

Criando o projeto

Para este exemplo basta criar um projeto utilizando um tipo básico Empty Activity e deixando todos os campos como default.

strings.xml

1<resources>
2    <string name="app_name">My Application</string>
3    <string name="name">Name:</string>
4    <string name="surname">Surname:</string>
5    <string name="join">Join</string>
6    <string name="clear">Clear</string>
7    <string name="full_name">Full Name:</string>
8</resources>

activity_main.xml

 1<?xml version="1.0" encoding="utf-8"?>
 2<android.support.constraint.ConstraintLayout
 3        xmlns:android="http://schemas.android.com/apk/res/android"
 4        xmlns:tools="http://schemas.android.com/tools"
 5        xmlns:app="http://schemas.android.com/apk/res-auto"
 6        android:layout_width="match_parent"
 7        android:layout_height="match_parent"
 8        tools:context=".MainActivity">
 9    <TextView
10            android:text="@string/name"
11            android:layout_width="wrap_content"
12            android:layout_height="wrap_content"
13            android:id="@+id/textViewName" android:layout_marginTop="8dp"
14            app:layout_constraintTop_toTopOf="parent" app:layout_constraintStart_toStartOf="parent"
15            android:layout_marginLeft="8dp" android:layout_marginStart="8dp"/>
16    <EditText
17            android:layout_width="0dp"
18            android:layout_height="wrap_content"
19            android:inputType="textPersonName"
20            android:ems="10"
21            android:id="@+id/editTextName" android:layout_marginTop="8dp"
22            app:layout_constraintTop_toBottomOf="@+id/textViewName" android:layout_marginStart="8dp"
23            app:layout_constraintStart_toStartOf="parent" android:layout_marginLeft="8dp" android:layout_marginEnd="8dp"
24            app:layout_constraintEnd_toEndOf="parent" android:layout_marginRight="8dp"/>
25    <TextView
26            android:text="@string/surname"
27            android:layout_width="wrap_content"
28            android:layout_height="wrap_content"
29            android:id="@+id/textViewSurname" android:layout_marginTop="8dp"
30            app:layout_constraintTop_toBottomOf="@+id/editTextName" app:layout_constraintStart_toStartOf="parent"
31            android:layout_marginLeft="8dp" android:layout_marginStart="8dp"/>
32    <EditText
33            android:layout_width="0dp"
34            android:layout_height="wrap_content"
35            android:inputType="textPersonName"
36            android:ems="10"
37            android:id="@+id/editTextSurname" android:layout_marginTop="8dp"
38            app:layout_constraintTop_toBottomOf="@+id/textViewSurname" android:layout_marginStart="8dp"
39            app:layout_constraintStart_toStartOf="parent" android:layout_marginLeft="8dp" android:layout_marginEnd="8dp"
40            app:layout_constraintEnd_toEndOf="parent" android:layout_marginRight="8dp"/>
41    <Button
42            android:text="@string/join"
43            android:layout_width="wrap_content"
44            android:layout_height="wrap_content"
45            android:id="@+id/buttonJoin" app:layout_constraintStart_toStartOf="parent" android:layout_marginLeft="8dp"
46            android:layout_marginStart="8dp" android:layout_marginTop="8dp"
47            app:layout_constraintTop_toBottomOf="@+id/editTextSurname"/>
48    <Button
49            android:text="@string/clear"
50            android:layout_width="wrap_content"
51            android:layout_height="wrap_content"
52            android:id="@+id/buttonClear" android:layout_marginTop="8dp"
53            app:layout_constraintTop_toBottomOf="@+id/editTextSurname" app:layout_constraintEnd_toEndOf="parent"
54            android:layout_marginEnd="8dp" android:layout_marginRight="8dp"/>
55    <TextView
56            android:text="@string/full_name"
57            android:layout_width="wrap_content"
58            android:layout_height="wrap_content"
59            android:id="@+id/textViewFull" android:layout_marginTop="8dp"
60            app:layout_constraintTop_toBottomOf="@+id/buttonJoin" app:layout_constraintStart_toStartOf="parent"
61            android:layout_marginLeft="8dp" android:layout_marginStart="8dp"/>
62    <EditText
63            android:layout_width="0dp"
64            android:layout_height="wrap_content"
65            android:inputType="textPersonName"
66            android:ems="10"
67            android:id="@+id/editTextFull" android:layout_marginTop="8dp"
68            app:layout_constraintTop_toBottomOf="@+id/textViewFull" android:layout_marginEnd="8dp"
69            app:layout_constraintEnd_toEndOf="parent" android:layout_marginRight="8dp" android:layout_marginStart="8dp"
70            app:layout_constraintStart_toStartOf="parent" android:layout_marginLeft="8dp"/>
71</android.support.constraint.ConstraintLayout>

MainActivity.kt

 1package com.example.myapplication
 2
 3import android.support.v7.app.AppCompatActivity
 4import android.os.Bundle
 5import android.widget.Button
 6import android.widget.EditText
 7
 8class MainActivity : AppCompatActivity() {
 9    override fun onCreate(savedInstanceState: Bundle?) {
10        super.onCreate(savedInstanceState)
11        setContentView(R.layout.activity_main)
12
13        val editTextName: EditText = findViewById(R.id.editTextName)
14        val editTextSurname: EditText = findViewById(R.id.editTextSurname)
15        val editTextFull: EditText = findViewById(R.id.editTextFull)
16        val buttonJoin: Button = findViewById(R.id.buttonJoin)
17        val buttonClear: Button = findViewById(R.id.buttonClear)
18
19        buttonJoin.setOnClickListener {
20            val full = "${editTextName.text} ${editTextSurname.text}"
21            editTextFull.setText(full)
22        }
23
24        buttonClear.setOnClickListener {
25            editTextName.text.clear()
26            editTextSurname.text.clear()
27            editTextFull.text.clear()
28        }
29    }
30}

Atividades

Faça um aplicativo para cálculo. O aplicativo deve armazenar os tipos de operações feitas e seus resultados. Ele também deve mostrar o histórico dos cálculos e deve haver um botão para desfazer os últimos cálculos executados. Veja abaixo uma sugestão de estrutura para o programa:

Veja que há várias formas de se trabalhar no exemplo e a imagem acima apresentada apenas uma sugestão. Você pode analisar e testar os componentes do android studio para tentar alcançar um resultado satisfatório pra você.