如何在 Java 中为多个组合使用复选框开关？

Question

This is my first post here so it may not be so well done... I'm a software development student and right now I'm learning Android Apps development.

I was asked to make a program with 4 checkboxes so when I checked any of them, the app shows a certain picture. For example.

Checkbox 1: Person.

Checkbox 2: Car.

Checkbox 3: Street.

Checkbox 4: Music.

If I checked 1(Person) and 2(Car), it should show a person and a car in the same picture... I was researching about this and I found this post . And I thought it was a good way to make this program, but I don't know how to make it work correctly. I tried doing this:

MainActivity.Java:

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.CheckBox;
import android.widget.ImageView;
public class MainActivity extends AppCompatActivity {

    CheckBox cb1, cb2, cb3, cb4;
    ImageView img;

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

        cb1 = findViewById(R.id.persona);
        cb2 = findViewById(R.id.car);
        cb3 = findViewById(R.id.calle);
        cb4 = findViewById(R.id.music);
        img = findViewById(R.id.imagen);

        int pattern = (cb1.isSelected() ? 0b0001 : 0)
                | (cb2.isSelected() ? 0b0010 : 0)
                | (cb3.isSelected() ? 0b0100 : 0)
                | (cb4.isSelected() ? 0b1000 : 0);
        switch (pattern) {

// No selection
            case 0b0000:

                img.setImageResource(R.drawable.def);

                break;

            //Person
            case 0b0001:

                img.setImageResource(R.drawable.wick);

                break;

            //Car
            case 0b0010:

                img.setImageResource(R.drawable.car);

                break;
        }
    }
}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    android:id="@+id/rl">

    <CheckBox
        android:id="@+id/persona"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/persona"
        android:layout_marginTop="25dp"
        android:checked="false"
        android:textSize="30sp"
        />

    <CheckBox
        android:id="@+id/car"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/car"
        android:layout_below="@id/persona"
        android:checked="false"
        android:textSize="30sp"
        />

    <CheckBox
        android:id="@+id/calle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/calle"
        android:layout_below="@id/car"
        android:checked="false"
        android:textSize="30sp"
        />

    <CheckBox
        android:id="@+id/music"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/music"
        android:layout_below="@id/calle"
        android:checked="false"
        android:textSize="30sp"
        />

    <ImageView
        android:id="@+id/imagen"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/music"
        android:layout_centerHorizontal="true"
        android:contentDescription="@string/imagen" />

</RelativeLayout>

But when I run the application, it only shows the default image(seems like only case 0b0000 works?), even if I make a specific checkbox checked="true" in the xml... I also tried making an onClick event for each checkbox to have it, but it seems like I'm not using the pattern variable the right way.

I would be very thankful if I get help... I think I could do it with Ifs, but I'm personally interested in that way I read in the post hahaha.

Answer 1

You need to attach listener to your checkboxes and move that pattern checking inside of onCheckedChanged() method. In this way, your checkboxes can notify activity and recalculate value of pattern :

public class MainActivity extends AppCompatActivity implements CompoundButton.OnCheckedChangeListener {

    CheckBox cb1, cb2, cb3, cb4;
    ImageView img;

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

        cb1 =  findViewById(R.id.persona);
        cb2 = findViewById(R.id.car);
        cb3 = findViewById(R.id.calle);
        cb4 = findViewById(R.id.music);
        img = findViewById(R.id.imagen);

        cb1.setOnCheckedChangeListener(this);
        cb2.setOnCheckedChangeListener(this);
        cb3.setOnCheckedChangeListener(this);
        cb4.setOnCheckedChangeListener(this);
    }

    @Override
    public void onCheckedChanged(CompoundButton compoundButton, boolean isChecked) {
        int pattern = (cb1.isChecked() ? 0b0001 : 0)
                | (cb2.isChecked() ? 0b0010 : 0)
                | (cb3.isChecked() ? 0b0100 : 0)
                | (cb4.isChecked() ? 0b1000 : 0);
        switch (pattern) {
            // No selection
            case 0b0000:
                img.setImageResource(R.drawable.def);
                break;
            //Person
            case 0b0001:
                img.setImageResource(R.drawable.wick);
                break;
            //Car
            case 0b0010:
                img.setImageResource(R.drawable.car);
                break;
        }
    }
}