[android] Android: View.setID(int id) programmatically - how to avoid ID conflicts?

I'm adding TextViews programmatically in a for-loop and add them to an ArrayList.

How do I use TextView.setId(int id)? What Integer ID do I come up with so it doesn't conflict with other IDs?

public String TAG() {
    return this.getClass().getSimpleName();
}

private AtomicInteger lastFldId = null;

public int generateViewId(){

    if(lastFldId == null) {
        int maxFld = 0;
        String fldName = "";
        Field[] flds = R.id.class.getDeclaredFields();
        R.id inst = new R.id();

        for (int i = 0; i < flds.length; i++) {
            Field fld = flds[i];

            try {
                int value = fld.getInt(inst);

                if (value > maxFld) {
                    maxFld = value;
                    fldName = fld.getName();
                }
            } catch (IllegalAccessException e) {
                Log.e(TAG(), "error getting value for \'"+ fld.getName() + "\' " + e.toString());
            }
        }
        Log.d(TAG(), "maxId="+maxFld +"  name="+fldName);
        lastFldId = new AtomicInteger(maxFld);
    }

    return lastFldId.addAndGet(1);
}

Just an addition to the answer of @phantomlimb,

while View.generateViewId() require API Level >= 17,
this tool is compatibe with all API.

according to current API Level,
it decide weather using system API or not.

so you can use ViewIdGenerator.generateViewId() and View.generateViewId() in the same time and don't worry about getting same id

import java.util.concurrent.atomic.AtomicInteger;

import android.annotation.SuppressLint;
import android.os.Build;
import android.view.View;

/**
 * {@link View#generateViewId()}??API Level >= 17,??????????API Level
 * <p>
 * ??????API Level,?????{@link View#generateViewId()},???????{@link View#generateViewId()}
 * ??,???????Id??
 * <p>
 * =============
 * <p>
 * while {@link View#generateViewId()} require API Level >= 17, this tool is compatibe with all API.
 * <p>
 * according to current API Level, it decide weather using system API or not.<br>
 * so you can use {@link ViewIdGenerator#generateViewId()} and {@link View#generateViewId()} in the
 * same time and don't worry about getting same id
 * 
 * @author [email protected]
 */
public class ViewIdGenerator {
    private static final AtomicInteger sNextGeneratedId = new AtomicInteger(1);

    @SuppressLint("NewApi")
    public static int generateViewId() {

        if (Build.VERSION.SDK_INT < 17) {
            for (;;) {
                final int result = sNextGeneratedId.get();
                // aapt-generated IDs have the high byte nonzero; clamp to the range under that.
                int newValue = result + 1;
                if (newValue > 0x00FFFFFF)
                    newValue = 1; // Roll over to 1, not 0.
                if (sNextGeneratedId.compareAndSet(result, newValue)) {
                    return result;
                }
            }
        } else {
            return View.generateViewId();
        }

    }
}

In order to dynamically generate View Id form API 17 use

generateViewId()

Which will generate a value suitable for use in setId(int). This value will not collide with ID values generated at build time by aapt for R.id.

Since API 17, the View class has a static method generateViewId() that will

generate a value suitable for use in setId(int)

(This was a comment to dilettante's answer but it got too long...hehe)

Of course a static is not needed here. You could use SharedPreferences to save, instead of static. Either way, the reason is to save the current progress so that its not too slow for complicated layouts. Because, in fact, after its used once, it will be rather fast later. However, I dont feel this is a good way to do it because if you have to rebuild your screen again (say onCreate gets called again), then you probably want to start over from the beginning anyhow, eliminating the need for static. Therefore, just make it an instance variable instead of static.

Here is a smaller version that runs a bit faster and might be easier to read:

int fID = 0;

public int findUnusedId() {
    while( findViewById(++fID) != null );
    return fID;
}

This above function should be sufficient. Because, as far as I can tell, android-generated IDs are in the billions, so this will probably return 1 the first time and always be quite fast. Because, it wont actually be looping past the used IDs to find an unused one. However, the loop is there should it actually find a used ID.

However, if you still want the progress saved between subsequent recreations of your app, and want to avoid using static. Here is the SharedPreferences version:

SharedPreferences sp = getSharedPreferences("your_pref_name", MODE_PRIVATE);

public int findUnusedId() {
    int fID = sp.getInt("find_unused_id", 0);
    while( findViewById(++fID) != null );
    SharedPreferences.Editor spe = sp.edit();
    spe.putInt("find_unused_id", fID);
    spe.commit();
    return fID;
}

This answer to a similar question should tell you everything you need to know about IDs with android: https://stackoverflow.com/a/13241629/693927

EDIT/FIX: Just realized I totally goofed up the save. I must have been drunk.

int fID;
do {
    fID = Tools.generateViewId();
} while (findViewById(fID) != null);
view.setId(fID);

...

public class Tools {
    private static final AtomicInteger sNextGeneratedId = new AtomicInteger(1);
    public static int generateViewId() {
        if (Build.VERSION.SDK_INT < 17) {
            for (;;) {
                final int result = sNextGeneratedId.get();
                int newValue = result + 1;
                if (newValue > 0x00FFFFFF)
                    newValue = 1; // Roll over to 1, not 0.
                if (sNextGeneratedId.compareAndSet(result, newValue)) {
                    return result;
                }
            }
        } else {
            return View.generateViewId();
        }
    }
}

My Choice:

// Method that could us an unique id

    int getUniqueId(){
        return (int)    
                SystemClock.currentThreadTimeMillis();    
    }

Also you can define ids.xml in res/values. You can see an exact example in android's sample code.

samples/ApiDemos/src/com/example/android/apis/RadioGroup1.java
samples/ApiDemp/res/values/ids.xml

This works for me:

static int id = 1;

// Returns a valid id that isn't in use
public int findId(){  
    View v = findViewById(id);  
    while (v != null){  
        v = findViewById(++id);  
    }  
    return id++;  
}

I use:

public synchronized int generateViewId() {
    Random rand = new Random();
    int id;
    while (findViewById(id = rand.nextInt(Integer.MAX_VALUE) + 1) != null);
    return id;
}

By using a random number I always have a huge chance of getting the unique id in first attempt.

The 'Compat' library now also supports the generateViewId() method for API levels prior 17.

Just make sure to use a version of the Compat library that is 27.1.0+

For example, in your build.gradle file, put :

implementation 'com.android.support:appcompat-v7:27.1.1

Then you can simply use the generateViewId() from the ViewCompat class instead of the View class as follow:

//Will assign a unique ID myView.id = ViewCompat.generateViewId()

Happy coding !

From API level 17 and above, you can call: View.generateViewId()

Then use View.setId(int).

If your app is targeted lower than API level 17, use ViewCompat.generateViewId()

inspired by @dilettante answer, here's my solution as an extension function in kotlin:

/* sets a valid id that isn't in use */
fun View.findAndSetFirstValidId() {
    var i: Int
    do {
        i = Random.nextInt()
    } while (findViewById<View>(i) != null)
    id = i
}

You can set ID's you'll use later in R.id class using an xml resource file, and let Android SDK give them unique values during compile time.

 res/values/ids.xml

<item name="my_edit_text_1" type="id"/>
<item name="my_button_1" type="id"/>
<item name="my_time_picker_1" type="id"/>

To use it in the code:

myEditTextView.setId(R.id.my_edit_text_1);