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!

score 127 · Accepted Answer · edited Jun 05 '19 at 03:23

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 05 '19 at 03:23

OneCricketeer

179,855
19
132
245

answered Feb 01 '11 at 16:44

WarrenFaith

57,492
25
134
150

24

"com.sample.project" can be replaced by getPackageName(). – jenzz Nov 17 '12 at 17:41
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. – Dave C Mar 28 '16 at 03:39
2

Note that in my experience doing this gives you very poor performance. – ThomasW Jun 28 '16 at 03:56

score 6 · Answer 2 · answered Feb 01 '11 at 16:39

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);
}

score 3 · Answer 3 · edited May 23 '17 at 11:55

3

Take a look at these answers:

edited May 23 '17 at 11:55

Community

1
1

answered Feb 01 '11 at 16:40

Cristian

198,401
62
356
264

1

@user573536 be aware that using `getResources().getIdentifier()` in a loop can cause performance to degrade when you have a large number of lookups. – dave.c Feb 01 '11 at 16:47
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). – Cristian Feb 01 '11 at 17:03

score 1 · Answer 4 · edited Mar 10 '16 at 18:51

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 '16 at 18:51

OneCricketeer

179,855
19
132
245

answered Feb 01 '11 at 16:42

Ganapathy C

5,989
5
42
75

score 0 · Answer 5 · answered Feb 01 '11 at 16:43

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());
            }
        }

score 0 · Answer 6 · answered Feb 01 '11 at 16:55

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 01 '11 at 16:55

Heiko Rupp

30,426
13
82
119

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()`. – dave.c Feb 01 '11 at 16:58
No sorry no idea. A view knows his children, so I don't think it is too bad. – Heiko Rupp Feb 01 '11 at 21:26

score 0 · Answer 7 · answered Apr 17 '18 at 23:08

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);

score 0 · Answer 8 · answered Jun 22 '21 at 16:34

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.

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

8 Answers8

Linked

Related