Masked Man Masked Man - 3 months ago 20
Android Question

Android View methods call order

I'm creating my own custom

NumberPicker
in android and here's the code:

package fs.mohammad.fun;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;

public class NumberPicker extends android.widget.NumberPicker {
private final static String LOG_TAG = "M3@NumberPicker";

public NumberPicker(Context context) {
super(context);
Log.d(LOG_TAG, "NumberPicker(context)");
}

public NumberPicker(Context context, AttributeSet attributeSet) {
super(context, attributeSet);
Log.d(LOG_TAG, "NumberPicker(context, attributeSet)");
}

@Override
public void addView(View child) {
super.addView(child);
Log.d(LOG_TAG, "addView(child)");
}

@Override
public void addView(View child, int index) {
super.addView(child, index);
Log.d(LOG_TAG, "addView(child, index)");
}

@Override
public void addView(View child, int width, int height) {
super.addView(child, width, height);
Log.d(LOG_TAG, "addView(child), width, height");
}

@Override
public void addView(View child, ViewGroup.LayoutParams params) {
super.addView(child, params);
Log.d(LOG_TAG, "addView(child, params)");
}

@Override
public void addView(View child, int index, ViewGroup.LayoutParams params) {
super.addView(child, index, params);
Log.d(LOG_TAG, "addView(child, index, params)");
}
}


and here's my layout code:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
android:id="@+id/root_view"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
tools:context="fs.mohammad.fun.MainActivity"
android:layout_width="match_parent"
android:layout_height="match_parent"
>

<fs.mohammad.fun.NumberPicker
android:id="@+id/number_picker"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_marginTop="50dp"
android:descendantFocusability="blocksDescendants"
/>

</RelativeLayout>


I expect that the constructor be called first but here's my Log output:

08-13 08:33:08.384 17759-17759/fs.mohammad.fun D/M3@NumberPicker: addView(child, index, params)
08-13 08:33:08.384 17759-17759/fs.mohammad.fun D/M3@NumberPicker: addView(child, params)
08-13 08:33:08.384 17759-17759/fs.mohammad.fun D/M3@NumberPicker: NumberPicker(context, attributeSet)


My question is why the
addView
is called before
constructor
?

Answer

NumberPicker inflates it's children in constructor. So NumberPicker#addView called by LayoutInflator to add children to NumberPicker.

Here is source code. https://github.com/android/platform_frameworks_base/blob/4535e11fb7010f2b104d3f8b3954407b9f330e0f/core/java/android/widget/NumberPicker.java#L678