(안드로이드) 버튼을 누르면 이전 이미지로 이동 // 토스트 메시지 알림창 표시

package com.slki.ex0323_2;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {
    ImageView imageView;
    Button prebtn;
    Button nexbtn;

    int cnt = 0;
    int imgs()={R.drawable.img1, R.drawable.img2,R.drawable.img3}; //배열로 담아주기

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

        imageView = findViewById(R.id.imageView);
        prebtn =(Button)findViewById(R.id.prebtn);
        nexbtn= (Button)findViewById(R.id.nexbtn);

        prebtn.setOnClickListener(mm);
        nexbtn.setOnClickListener(mm);


    }
    public void btnClick(View v) {
        if (v.getId() == R.id.btn1) {
            cnt=0;
           // Log.i("이미지", "index:" +"1번");
        } else if (v.getId() == R.id.btn2) {
            cnt=1;
           // Log.i("이미지", "index:" +"2번");
        }else if (v.getId() == R.id.btn3) {
            cnt=2;
           // Log.i("이미지","index:" +"3번");
        }

        imageView.setImageResource(imgs(cnt));
    }

    View.OnClickListener mm = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
//          Log.i("이미지", "index:" + (cnt+1));
            switch (v.getId()) {
                case R.id.prebtn:
                    if (cnt > 0) {
                        imageView.setImageResource(imgs(--cnt));
                    } else {
                        cnt = 2;
                        imageView.setImageResource(imgs(cnt));

                    }
                    break;
                case R.id.nexbtn:
                    if (cnt < imgs.length -1 ) {
                        imageView.setImageResource(imgs(++cnt));
                    } else {
                        cnt = 0;
                        imageView.setImageResource(imgs(cnt));
                    }

                }

            }
        };

    }

package com.slki.ex0323_2;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    ImageView imageView;


    int cnt = 0;
    int imgs()={R.drawable.img1, R.drawable.img2,R.drawable.img3}; //배열로 담아주기

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

        imageView = findViewById(R.id.imageView);


    }
    public void btnClick(View v) {
        if (v.getId() == R.id.btn1) {
            cnt = 0;
        } else if (v.getId() == R.id.btn2) {
            cnt = 1;
        } else if (v.getId() == R.id.btn3) {
            cnt = 2;
        } else if (v.getId() == R.id.prebtn) {
            if (cnt != 0) {
                cnt--;
            } else {
                cnt = imgs.length-1;
                Toast.makeText(this, "마지막 사진으로 돌아갑니다.", Toast.LENGTH_SHORT).show();
            }
        } else if (v.getId() == R.id.nexbtn) {
            if (cnt !=  imgs.length-1) {
                cnt++;
            } else {
                cnt = 0;
                Toast.makeText(this, "첫번째 사진으로 돌아갑니다. ", Toast.LENGTH_SHORT).show();
            }
        }

        imageView.setImageResource(imgs(cnt));

    } //btnClick 끝



}