An implementation of a "findViewsByTag" method on Android

strings.xml

<resources>

    <string name="tag">tag:touchMe</string>
    <string name="touch_me">Touch me!</string>

</resources>

ViewAdditions.java

package com.cyrilmottier.android.tests;

import android.view.View;
import android.view.ViewGroup;

/**
 * @author Cyril Mottier
 */
public class ViewAdditions {

    public interface OnTagFoundHandler {
        void onTagFound(View v);
    }

    public static final void findViewsByTag(View root, String tag, OnTagFoundHandler handler) {
        if (root == null) {
            throw new NullPointerException();
        }
        if (tag == null || handler == null) {
            return;
        }
        if (tag.equals(root.getTag())) {
            handler.onTagFound(root);
        }
        if (root instanceof ViewGroup) {
            final ViewGroup rootGroup = (ViewGroup) root;
            final int childCount = rootGroup.getChildCount();
            for (int i = 0; i < childCount; i++) {
                findViewsByTag(rootGroup.getChildAt(i), tag, handler);
            }
        }
    }

}

ViewAdditionsActivity.java

package com.cyrilmottier.android.tests;

import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.Toast;

import com.cyrilmottier.android.tests.ViewAdditions.OnTagFoundHandler;

/**
 * @author Cyril Mottier
 */
public class ViewAdditionsActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.view_additions_activity);

        ViewAdditions.findViewsByTag(findViewById(R.id.root), getString(R.string.tag), new OnTagFoundHandler() {
            @Override
            public void onTagFound(View v) {
                v.setOnTouchListener(mOnTouchListener);
            }
        });
    }

    private OnTouchListener mOnTouchListener = new OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    Toast.makeText(getApplicationContext(), "ACTION_DOWN fired", Toast.LENGTH_SHORT).show();
                    break;
            }
            return true;
        }
    };

}

views_additions_activity.xml

<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/root"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:columnCount="2"
    android:useDefaultMargins="true" >

    <TextView
        android:background="#dedede"
        android:ellipsize="end"
        android:gravity="center"
        android:padding="16dp"
        android:tag="@string/tag"
        android:text="@string/touch_me" />

    <TextView
        android:background="#dedede"
        android:ellipsize="end"
        android:gravity="center"
        android:padding="16dp"
        android:tag="@string/tag"
        android:text="@string/touch_me" />

    <TextView
        android:background="#dedede"
        android:ellipsize="end"
        android:gravity="center"
        android:padding="16dp"
        android:tag="@string/tag"
        android:text="@string/touch_me" />

    <TextView
        android:background="#dedede"
        android:ellipsize="end"
        android:gravity="center"
        android:padding="16dp"
        android:tag="@string/tag"
        android:text="@string/touch_me" />

</GridLayout>

Interesting idea. Also problem is that it uses android:tag and therefore prevent you from using the tag for another use (for example a ViewHolder)

Another thing is I don't know if it's faster (in term of execution) to use that instead of a bunch of findViewById ...

Sorry, I just saw your comment ... GitHub is not notifying me when someone is commenting a Gist :(.

Of course it uses the tag but that's not a big issue as you can still add tags using the setTag(int, Object) method.

Regarding the findViewById(int), the main issue is an identifier is supposed to be unique. Android lets you do what ever you want with it so you could do the exact same thing with findViewById(int) but it doesn't sounds right to me :)