Declaring a LinearLayout from Android 3.0 Cookbook Chapter 2 - android-linearlayout

Question

I'm following the instructions from chapter 2 (Declaring a layout) from the Android 3.0 Application Development Cookbook, and I can't seem to get it to work. Here's the code:
The book has you edit the main.xml file so that it looks like this in res/layout/activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView
android:text="#string/vertical"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<Button
android:text="#string/button_click_horizontal"
android:id="#+id/horizontal_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
Then, as second step, it asks you make a copy of the activity_main.xml file and name it my_layout.xml, and its code looks like this (res/layout/my_layout.xml):
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView
android:text="#string/horizontal"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<Button
android:text="#string/click_for_vertical"
android:id="#+id/vertical_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
And the code for the main activity file looks like this:
package com.example.declaringlayouts;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
public class MainActivity extends Activity implements View.OnClickListener {
private Button mHorizontalButton;
private Button mVerticalButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mVerticalButton = (Button) findViewById(R.id.vertical_button);
mHorizontalButton = (Button) findViewById(R.id.horizontal_button);
}
#Override
public void onClick(View view) {
if (view == mHorizontalButton) {
setContentView(R.layout.activity_main);
} else if (view == mVerticalButton) {
setContentView(R.layout.my_layout);
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
The idea is that clicking in horizontal button will switch to the vertical layout, and vice-versa. Clicking on the button does not work at all.

Answer 1

You need to tell the buttons that this class is the onClickListener, so that it will call your onClick method when they are clicked.
This has to be set up every time you create a new content view, so you should put your button reference setup and listener assignment into a method. So this is how I would revise the class:
public class MainActivity extends Activity implements View.OnClickListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
prepareButtons();
}
void prepareButtons(){
Button button = (Button) findViewById(R.id.vertical_button);
if (button==null)
button = (Button) findViewById(R.id.horizontal_button);
mVerticalButton.setOnClickListener(this);
mHorizontalButton.setOnClickListener(this);
}
#Override
public void onClick(View view) {
if (view == mHorizontalButton) {
setContentView(R.layout.activity_main);
prepareButtons();
} else if (view == mVerticalButton) {
setContentView(R.layout.my_layout);
prepareButtons();
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}