Android: Using findViewById() with a string / in a loop

Question

I'm making an android application, where there is a view composed of hundreds of buttons, each with a specific callback. Now, I'd like to set these callbacks using a loop, instead of having to write hundreds of lines of code (for each one of the buttons).

My question is: How can I use findViewById without statically having to type in each button id? Here is what I would like to do:

    for(int i=0; i<some_value; i++) {
       for(int j=0; j<some_other_value; j++) {
        String buttonID = "btn" + i + "-" + j;
        buttons[i][j] = ((Button) findViewById(R.id.buttonID));
        buttons[i][j].setOnClickListener(this);
       }
    }

Thanks in advance!

OneCricketeer · Accepted Answer · 2019-06-05 03:23:06Z

127

You should use getIdentifier()

for(int i=0; i<some_value; i++) {
   for(int j=0; j<some_other_value; j++) {
    String buttonID = "btn" + i + "-" + j;
    int resID = getResources().getIdentifier(buttonID, "id", getPackageName());
    buttons[i][j] = ((Button) findViewById(resID));
    buttons[i][j].setOnClickListener(this);
   }
}

edited Jun 5, 2019 at 3:23

OneCricketeer

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answered Feb 1, 2011 at 16:44

WarrenFaith

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3 Comments

jenzz Over a year ago

"com.sample.project" can be replaced by getPackageName().

Dave C Over a year ago

I'd seen other answers very similar to this, but the second arg being "id" was the last thing I needed for it to work.

ThomasW Over a year ago

Note that in my experience doing this gives you very poor performance.

Rick Barkhouse · Accepted Answer · 2011-02-01 16:39:57Z

6

You can try making an int[] that holds all of your button IDs, and then iterate over that:

int[] buttonIDs = new int[] {R.id.button1ID, R.id.button2ID, R.id.button3ID, ... }

for(int i=0; i<buttonIDs.length; i++) {
    Button b = (Button) findViewById(buttonIDs[i]);
    b.setOnClickListener(this);
}

answered Feb 1, 2011 at 16:39

Rick Barkhouse

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Comments

Community · Accepted Answer · 2017-05-23 11:55:04Z

3

Take a look at these answers:

edited May 23, 2017 at 11:55

CommunityBot

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answered Feb 1, 2011 at 16:40

Cristian

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2 Comments

dave.c Over a year ago

@user573536 be aware that using getResources().getIdentifier() in a loop can cause performance to degrade when you have a large number of lookups.

Cristian Over a year ago

You are right. I recommend that approach only when there's a sequence or order for the resources AND there are a lot of them (creating an array of 50 resources smells).

OneCricketeer · Accepted Answer · 2016-03-10 18:51:51Z

1

you can Use tag if you want to access.

in onClick

int i=Integer.parseInt(v.getTag);

But you cant access that button like this.

simply create button programatically

by Button b=new Button(this);

edited Mar 10, 2016 at 18:51

OneCricketeer

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answered Feb 1, 2011 at 16:42

Ganapathy C

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Comments

Sankar Ganesh PMP · Accepted Answer · 2011-02-01 16:43:21Z

0

create Custom Button in java code rather in Xml as i shown below

Button bs_text[]= new Button[some_value];

    for(int z=0;z<some_value;z++)
        {
            try
            {

            bs_text[z]   =  (Button) new Button(this);

            }
            catch(ArrayIndexOutOfBoundsException e)
            {
                Log.d("ArrayIndexOutOfBoundsException",e.toString());
            }
        }

answered Feb 1, 2011 at 16:43

Sankar Ganesh PMP

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Comments

Heiko Rupp · Accepted Answer · 2011-02-01 16:55:27Z

0

If your top level view only has those button views as children, you could do

for (int i = 0 ; i < yourView.getChildCount(); i++) {
    Button b = (Button) yourView.getChildAt(i);
    b.setOnClickListener(xxxx);
}

If there are more views present you'd need to check if the selected one is one of your buttons.

answered Feb 1, 2011 at 16:55

Heiko Rupp

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2 Comments

dave.c Over a year ago

do you know how the performance compares with the other suggested methods? I'd assume that it was slightly slower than an array of ID's, but I'd be interested to know how it compares with getResources().getIdentifier().

Heiko Rupp Over a year ago

No sorry no idea. A view knows his children, so I don't think it is too bad.

B.Cakir · Accepted Answer · 2018-04-17 23:08:36Z

0

If for some reason you can't use the getIdentifier() function and/or you know the possible id's beforehand, you could use a switch.

int id = 0;

switch(name) {
    case "x":
        id = R.id.x;
        break;
    etc.etc.
}

String value = findViewById(id);

answered Apr 17, 2018 at 23:08

B.Cakir

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Comments

Mihkuno · Accepted Answer · 2021-06-22 16:34:14Z

0

To put it simply, here's a function for it

public View findViewByArrayName (String name, int i) {
        buttonID = name + Integer.toString(i);
        resID = getResources().getIdentifier(buttonID, "id", getPackageName());
        return findViewById(resID);
    }

Also unlike Python, Java is a compiled language, so it probably makes sense that there aren't any chances for dynamic variable names. Unless achieved through a certain approach like this one.

answered Jun 22, 2021 at 16:34

Mihkuno

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