How to move backwards in an array list on button click?

Question

I want to move backwards in an array-list when i press a button (previous), I already did how to move next, but the previous button crashes at a point. I want it to move backwards in an array list from a point where the next button left and then stop at the 0 element.

I already tried doing this in the code below:

package com.learn.vocabularyapp;

import android.animation.ObjectAnimator;
import android.content.Context;
import android.content.SharedPreferences;
import android.graphics.drawable.Drawable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.animation.AccelerateDecelerateInterpolator;
import android.view.animation.DecelerateInterpolator;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.TextView;

import org.w3c.dom.Text;

public class Colors extends AppCompatActivity {
    Context context= this;
    String encolor;
    int iteratoren;
    int iteratorar;
    String arcolor;


    final String MYPRG = "myprg";
    int prgbar = 50;
    int pbOption = 20;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_colors);

        final ProgressBar myprg = (ProgressBar) findViewById(R.id.myprg);


        final Drawable setimg = getResources().getDrawable(R.drawable.tick);

        final ImageView done = (ImageView) findViewById(R.id.done);

        final String[] colorsen = context.getResources().getStringArray(R.array.colorsen);
        final TextView coloren = (TextView) findViewById(R.id.colorsen);
        final TextView colorar = (TextView) findViewById(R.id.colorsar);
        final String[] colorsar = context.getResources().getStringArray(R.array.colorsar);



        for (int i = 0; i < colorsen.length; i ++) {
            encolor = colorsen[i];
        }
        for (int i = 0; i < colorsar.length; i ++ ) {
            arcolor = colorsar[i];
        }

        Button next = (Button) findViewById(R.id.next);
        next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

            encolor = colorsen[iteratoren];
            arcolor = colorsar[iteratorar];

            coloren.setText(encolor);
            colorar.setText(arcolor);


            iteratorar++;
            iteratoren++;

            if (iteratorar >= colorsar.length) {
                iteratorar = 0;
            }

            if (iteratoren >= colorsen.length) {
                iteratoren = 0;
            }
            myprg.setProgress(myprg.getProgress()+20/3);
            if (myprg.getProgress() == 100) {
                done.setImageDrawable(setimg);
            }

            }
        });

        Button previous = (Button) findViewById(R.id.prev);
        previous.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                encolor = colorsen[iteratoren];
                arcolor = colorsar[iteratorar];

                coloren.setText(encolor);
                colorar.setText(arcolor);


                iteratorar--;
                iteratoren--;

                if (iteratorar >= colorsar.length) {
                    iteratorar = 14;
                }

                if (iteratoren >= colorsen.length) {
                    iteratoren = 14;
                }

                myprg.setProgress(myprg.getProgress()-20/3);
                done.setImageDrawable(null);
            }
        });

strings.xml file:

 <string-array name="colorsen">
        <item>Red</item>
        <item>Orange</item>
        <item>Yellow</item>
        <item>Green</item>
        <item> Blue</item>
        <item> Purple</item>
        <item>Brown</item>
        <item> Magenta</item>
        <item> Tan</item>
        <item> Cyan</item>
        <item> Maroon</item>
        <item> Silver</item>
        <item> Pink</item>
        <item>Black</item>
        <item> White</item>
        <item>Gold</item>
    </string-array>

    <string-array name="colorsar">
        <item>أحمر</item>
        <item>البرتقالي</item>
        <item>الأصفر</item>
        <item>أخضر</item>
        <item>بَنَفْسَجي</item>
        <item>بنى</item>
        <item>أرجواني</item>
        <item>سُمْرة</item>
        <item>السماوي</item>
        <item>كَسْتَنائيّ</item>
        <item>لَوْن فِضّيّ</item>
        <item>زهري</item>
        <item>أسود</item>
        <item>أبيض</item>
        <item>لون ذهبي</item>
    </string-array>

I am a beginner in android and java so a detailed answer would be appreciated.

william xyz · Accepted Answer · 2019-05-19 18:06:42Z

1

According to your logic, you could change the code:

if (iteratorar >= colorsar.length) {
    iteratorar = 14;
}
if (iteratoren >= colorsen.length) {
    iteratoren = 14;
}

to:

if (iteratorar < 0) {
    iteratorar = 0;
}
if (iteratoren < 0) {
    iteratoren = 0;
}

This would prevent it from crashing when you get to the leftmost item and press previous.

answered May 19, 2019 at 18:06

william xyz

1,0891 gold badge8 silver badges24 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

a fair player · Accepted Answer · 2019-05-19 18:07:56Z

0

you need to make sure that you stop at index 0. having iteratorar--; and iteratoren--; will cause the index to fall to -1 and crashes the app. So, you can do one of 2 things:

checking the values of iteratorar--; and iteratoren--; to make sure that you don't reach/use -1. some thing like if(iteratorar == 0) {return;}
once the index reaches 0, you set the values of iteratorar--; and iteratoren--; to the (sizeOfTheArray - 1), which will allow you rotate from the end again.

Hope you get the idea

answered May 19, 2019 at 18:07

a fair player

11.8k10 gold badges48 silver badges51 bronze badges

Collectives™ on Stack Overflow

How to move backwards in an array list on button click?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related