How can i cycle array values with next and previous button in Android

Question

I am developing a vocabulary application and i want to cycle array values with next and previous buttons. I assigned values from Database and working. But i cant cycle between array values. Increasing working but i have to click several times to cycle previous value. I could not find the correct increment, decrement operator.

 int position = 0; 
`btnNext.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(position >= array.length){
                position = 0;
                txtWord.setText(array[position][0]);
                position++;                    
            }else {
                txtWord.setText(array[position][0]);
                position++;                   
            }
        }
    });`

btnBack.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(position >= 0){
                txtWord.setText(array[position--][0]);
            }else{
                position = array.length;
                txtWord.setText(array[position--][0]);
            }

        }
    });

Complete Code is here:

DatabaseHelper myDB;
TextView txtWord, txtNumberOfWords;
Button btnBack, btnShow, btnNext;
String[][] array;
int position = 0;
boolean showWord= true;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar myToolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(myToolbar);

    txtWord = (TextView)findViewById(R.id.txtWord);
    txtNumberOfWords = (TextView)findViewById(R.id.txtNumberOfWords);
    btnBack = (Button)findViewById(R.id.btnBack);
    btnShow = (Button)findViewById(R.id.btnShow);
    btnNext = (Button)findViewById(R.id.btnNext);

    myDB = new DatabaseHelper(this);


    Cursor data = myDB.getListContents();
    array = new String[data.getCount()][2];

    if(data.getCount() == 0){
        Toast.makeText(MainActivity.this, "There is no definition!", Toast.LENGTH_LONG).show();
    }else{

        data.moveToFirst();

        for(int i = 0; i < data.getCount(); i++){
                for(int y = 0; y < 2; y++){
                    array[i][y] = data.getString(1+y);
                }
                data.moveToNext();
            }
        txtWord.setText(array[0][0]);
        position = position + 1;
        txtNumberOfWords.setText(position  + " of " + array.length);
    }

    btnNext.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(position >= array.length){
                position = 0;
                txtWord.setText(array[position][0]);
                position++;
                txtNumberOfWords.setText(position  + " of " + array.length);
            }else {
                txtWord.setText(array[position][0]);
                position++;
                txtNumberOfWords.setText(position  + " of " + array.length);
            }
            showWord = true;
        }
    });

    btnBack.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(position >= 0){
                txtWord.setText(array[position--][0]);
                txtNumberOfWords.setText(position  + " of " + array.length);
            }else{
                position = array.length;
                txtWord.setText(array[position--][0]);
                txtNumberOfWords.setText(position  + " of " + array.length);
            }

        }
    });

    btnShow.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(showWord){
                txtWord.setText(array[position-1][1]);
                showWord = false;
            }else{
                txtWord.setText(array[position-1][0]);
                showWord = true;
            }
        }
    });
}

Martin · Accepted Answer · 2018-08-30 16:25:32Z

1

Try this

    btnNext.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            position = (position + 1) % array.length;
            txtWord.setText(array[position][0]);
        }
    });

    btnBack.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            position = (position - 1) % array.length;
            txtWord.setText(array[position][0]);
        }
    });

There's also a bug, as you're using position as both the TextView - txtNumberOfWords and the array pointer. Those are different. For the TextView, display position+1 and for the array use position. Don't forget to change your line of code from:

position = position + 1;

to this:

position = 0;

edited Aug 30, 2018 at 16:25

answered Aug 30, 2018 at 15:52

Martin

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7 Comments

venovar Over a year ago

Its not working stable. For example Values jump from first to third.

Martin Over a year ago

Try setting position to 0, instead of position + 1;

venovar Over a year ago

the above code i wrote, works fine in the forward direction.

Martin Over a year ago

Yes, it's jumping from first to third because your position is set wrong. Set it to 0 before the clickListeners. And for the the textView (txtNumberOfWords), display position+1

venovar Over a year ago

Ohh finally, yes, increment and decrement working now. But when i try to come back from array [0][0] value, app crashes. No problem forward direction. It cycles correctly. Should i use if statement? For example if(position <= 0){ position = array.length;}. Thank you by the way.

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