Densidades independentes de pixels

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Exemplos práticos (App Lanchonete)

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"
    android:padding="16dp">
    <ImageView
        android:id="@+id/imageViewBolo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/bolo_de_fuba"
        android:layout_gravity="center"
        android:contentDescription="Imagem de bolo"
        android:layout_marginBottom="16dp"/>
    <ImageView
        android:id="@+id/imageViewCafe"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/coffee"
        android:layout_gravity="center"
        android:contentDescription="Imagem de café"
        android:layout_marginBottom="16dp"/>
    <TextView
        android:id="@+id/textViewTotal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="R$ 0.00"
        android:textSize="20sp"/>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical" >
        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:text="*** Usando TableRow ***"
            android:textAppearance="@style/TextAppearance.AppCompat.Large"/>
    <TableRow android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <ImageView
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:src="@drawable/coffee"/>
        <ImageView
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:src="@drawable/bolo_de_fuba"/>
    </TableRow>
    <TableRow
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <TextView android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:background="@color/blue"
            android:gravity="center"
            android:text="Café"
            android:textAppearance="@style/TextAppearance.AppCompat.Medium"/>
        <TextView android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:background="@color/green"
            android:gravity="center"
            android:text="Bolo"
            android:textAppearance="@style/TextAppearance.AppCompat.Medium"/>
    </TableRow>
    </LinearLayout>
</LinearLayout>

activity_cafe.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"
    android:padding="16dp">
    <EditText
        android:id="@+id/editTextQuantidadeCafe"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Quantidade:"
        android:inputType="number"
        android:layout_marginBottom="16dp"/>
    <Button
        android:id="@+id/buttonCafe"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Adicionar Café"/>
</LinearLayout>

activity_bolo.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"
    android:padding="16dp">
    <EditText
        android:id="@+id/editTextQuantidadeBolo"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Quantidade:"
        android:inputType="number"
        android:layout_marginBottom="16dp"/>
    <Button
        android:id="@+id/buttonBolo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Adicionar Bolo"/>
</LinearLayout>

CalculoModel.java

public class CalculoModel {
    private double total;
    private static final double CAFE_PRECO = 2.50;
    private static final double BOLO_PRECO = 5.00;
    public CalculoModel() {
        this.total = 0.0;
    }
    public double getTotal() {
        return total;
    }
    public void setTotal(double total) {
        this.total = total;
    }
    public void addCafe(int quantidade) {
        total += quantidade * CAFE_PRECO;
    }
    public void addBolo(int quantidade) {
        total += quantidade * BOLO_PRECO;
    }
}

MainActivity.java

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
public class MainActivity extends AppCompatActivity
        implements View.OnClickListener {
    private ImageView imageViewBolo;
    private ImageView imageViewCafe;
    private TextView textViewTotal;
    private CalculoModel model;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        imageViewBolo = findViewById(R.id.imageViewBolo);
        imageViewCafe = findViewById(R.id.imageViewCafe);
        textViewTotal = findViewById(R.id.textViewTotal);
        model = new CalculoModel();
        imageViewBolo.setOnClickListener(this);
        imageViewCafe.setOnClickListener(this);
        Intent intent = getIntent();
        if (intent != null && intent.hasExtra("total")) {
            model.setTotal(intent.getDoubleExtra("total",
                    0.0));
            Log.e("Main",""+model.getTotal());
            alterarTotal();
        }
    }
    @Override
    public void onClick(View view) {
        int viewId = view.getId();
        if (viewId == R.id.imageViewBolo) {
            Intent intentBolo = new Intent(this,
                    BoloActivity.class);
            intentBolo.putExtra("total", model.getTotal());
            startActivity(intentBolo);
        } else if (viewId == R.id.imageViewCafe) {
            Intent intentCafe = new Intent(this,
                    CafeActivity.class);
            intentCafe.putExtra("total", model.getTotal());
            startActivity(intentCafe);
        }
    }
    // alterar a view com o valor obtido do modelo
    private void alterarTotal() {
        textViewTotal.setText(String.format("R$ %.2f", model.getTotal()));
    }
}

CafeActivity.java

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import androidx.appcompat.app.AppCompatActivity;
public class CafeActivity extends AppCompatActivity implements View.OnClickListener {
    private EditText editTextQuantidadeCafe;
    private Button buttonCafe;
    private CalculoModel model;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_cafe);
        editTextQuantidadeCafe = findViewById(R.id.editTextQuantidadeCafe);
        buttonCafe = findViewById(R.id.buttonCafe);
        model = new CalculoModel();
        buttonCafe.setOnClickListener(this);
        Intent intent = getIntent();
        if (intent != null && intent.hasExtra("total")) {
            model.setTotal(intent.getDoubleExtra("total",
                    0.0));
            Log.e("Main",""+model.getTotal());
        }
    }
    @Override
    public void onClick(View view) {
        if (view.getId() == R.id.buttonCafe) {
            try {
                int quantidade = Integer.parseInt(editTextQuantidadeCafe.getText().toString());
                model.addCafe(quantidade);
                Intent intent = new Intent(this, MainActivity.class);
                intent.putExtra("total", model.getTotal());
                startActivity(intent);
            } catch (NumberFormatException e) {
                editTextQuantidadeCafe.setError("Por favor, insira um número válido");
            }
        }
    }
}

BoloActivity.java

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import androidx.appcompat.app.AppCompatActivity;
public class BoloActivity extends AppCompatActivity implements View.OnClickListener {
    private EditText editTextQuantidadeBolo;
    private Button buttonBolo;
    private CalculoModel model;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_bolo);
        editTextQuantidadeBolo = findViewById(R.id.editTextQuantidadeBolo);
        buttonBolo = findViewById(R.id.buttonBolo);
        model = new CalculoModel();
        buttonBolo.setOnClickListener(this);
        Intent intent = getIntent();
        if (intent != null && intent.hasExtra("total")) {
            model.setTotal(intent.getDoubleExtra("total", 0.0));
            Log.e("Main",""+model.getTotal());
        }
    }
    @Override
    public void onClick(View view) {
        if (view.getId() == R.id.buttonBolo) {
            try {
                int quantidade = Integer.parseInt(editTextQuantidadeBolo.getText().toString());
                model.addBolo(quantidade);
                Intent intent = new Intent(this, MainActivity.class);
                intent.putExtra("total", model.getTotal());
                startActivity(intent);
            } catch (NumberFormatException e) {
                editTextQuantidadeBolo.setError("Por favor, insira um número válido");
            }
        }
    }
}

Exemplos práticos (IMC)

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"
    android:padding="16dp"
    android:gravity="center">
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Informe seus dados:"
        android:layout_marginBottom="16dp" />
    <EditText
        android:id="@+id/editTextNome"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Nome"
        android:inputType="textPersonName" />
    <EditText
        android:id="@+id/editTextIdade"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Idade"
        android:inputType="number" />
    <EditText
        android:id="@+id/editTextAltura"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Altura (em metros)"
        android:inputType="numberDecimal" />
    <EditText
        android:id="@+id/editTextPeso"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Peso (em kg)"
        android:inputType="numberDecimal" />
    <Button
        android:id="@+id/buttonCalcular"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Calcular IMC"
        android:layout_marginTop="16dp" />
    <TextView
        android:id="@+id/textViewResultado"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=""
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        android:layout_marginTop="16dp" />
</LinearLayout>

MainActivity.java

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
public class MainActivity extends AppCompatActivity {
    private EditText editTextNome, editTextIdade,
            editTextAltura, editTextPeso;
    private TextView textViewResultado;
    private Button buttonCalcular;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editTextNome = findViewById(R.id.editTextNome);
        editTextIdade = findViewById(R.id.editTextIdade);
        editTextAltura = findViewById(R.id.editTextAltura);
        editTextPeso = findViewById(R.id.editTextPeso);
        buttonCalcular = findViewById(R.id.buttonCalcular);
        textViewResultado = findViewById(R.id.textViewResultado);
        buttonCalcular.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String nome = editTextNome.getText().toString();
                int idade = Integer.parseInt(editTextIdade.getText().toString());
                double altura = Double.parseDouble(editTextAltura.getText().toString());
                double peso = Double.parseDouble(editTextPeso.getText().toString());
                Pessoa pessoa = new Pessoa(nome, idade, altura, peso);
                double imc = pessoa.calcularIMC();
                textViewResultado.setText("Nome: " + pessoa.getNome() + "\nIMC: " + String.format("%.2f", imc));
            }
        });
    }
}

Pessoa.java

public class Pessoa {
    private String nome;
    private int idade;
    private double altura;
    private double peso;
    public Pessoa(String nome, int idade, double altura, double peso) {
        this.nome = nome;
        this.idade = idade;
        this.altura = altura;
        this.peso = peso;
    }
    public double calcularIMC() {
        return peso / (altura * altura);
    }
    public String getNome() {
        return nome;
    }
}

Exemplos práticos (Calculadora)

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"
    android:padding="16dp"
    android:gravity="center">
    <EditText
        android:id="@+id/editTextNumero1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Número 1"
        android:inputType="number" />
    <EditText
        android:id="@+id/editTextNumero2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Número 2"
        android:inputType="number" />
    <Button
        android:id="@+id/buttonSomar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Somar" />
    <Button
        android:id="@+id/buttonSubtrair"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Subtrair" />
    <TextView
        android:id="@+id/textViewResultado"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Resultado: "
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        android:layout_marginTop="20dp" />
</LinearLayout>

MainActivity.java

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
public class MainActivity extends AppCompatActivity {
    private EditText editTextNumero1, editTextNumero2;
    private Button buttonSomar, buttonSubtrair;
    private TextView textViewResultado;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editTextNumero1 = findViewById(R.id.editTextNumero1);
        editTextNumero2 = findViewById(R.id.editTextNumero2);
        buttonSomar = findViewById(R.id.buttonSomar);
        buttonSubtrair = findViewById(R.id.buttonSubtrair);
        textViewResultado = findViewById(R.id.textViewResultado);
        buttonSomar.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String numero1 = editTextNumero1.getText().toString();
                String numero2 = editTextNumero2.getText().toString();
                int num1 = Integer.parseInt(numero1);
                int num2 = Integer.parseInt(numero2);
                int resultado = Calculadora.somar(num1, num2);
                textViewResultado.setText("Resultado da soma: " + resultado);
            }
        });
        buttonSubtrair.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String numero1Str = editTextNumero1.getText().toString();
                String numero2Str = editTextNumero2.getText().toString();
                int num1 = Integer.parseInt(numero1Str);
                int num2 = Integer.parseInt(numero2Str);
                int resultado = Calculadora.subtrair(num1, num2);
                textViewResultado.setText("Resultado da subtração: " + resultado);
            }
        });
    }
}

Calculadora.java

public class Calculadora {
    public static int somar(int num1, int num2) {
        return num1 + num2;
    }
    public static int subtrair(int num1, int num2) {
        return num1 - num2;
    }
}