findViewById in onCreate returns NULL when using Fragment

How to change the image dynamically in ImageView and button setOnClickListener Android sample.


Main.java

ipackage cz.okhelp.my_game;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;


public class Main extends Activity {
private ImageView hImageViewSemafor;
private Button hButton;
	
	@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        hImageViewSemafor = (ImageView)findViewById(R.id.idImageViewSemafor);
        hButton = (Button) findViewById(R.id.idBtnChangeImage);
        hButton.setOnClickListener(mButtonChangeImageListener);
 
 
       
       
    }
	
    View.OnClickListener mButtonChangeImageListener = new OnClickListener() {
        public void onClick(View v) {
                // setImageResource will change image in ImageView
        	hImageViewSemafor.setImageResource(R.drawable.semafor_green);
            
        }
    };

}

main.xml
Put into res/drawable this pictures:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="//schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
    
       <ImageView
            android:src="@drawable/semafor_red"
            android:id="@+id/idImageViewSemafor"
            android:background="#66FFFFFF"
            android:adjustViewBounds="true"
            android:maxWidth="47dip"
            android:maxHeight="91dip"
            android:padding="10dip"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />    
    
</LinearLayout>

If using Wordpress:
- update Wordpress
- download Plugin Any Mobile Theme Switcher and upzip into yourweb/wp-content/plugins/
- open Wordpress Dachboard on yourweb
- set defalut theme for desktop (Appearance - Theme)
- set themes for mobile users Settings - Any Mobile Theme Switcher for example Twentyfourteen theme
- preview page
- test page on Mobile Friendly Test

Log.e println needs a message error.
E/AndroidRuntime(330): FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{b.paint/b.paint.MainActivity}: java.lang.NullPointerException: println needs a message

Try this code:

		// Error
                String s = null;
		Log.e("bla", s); // !!! error Log.e println needs a message error.
                // OK
		String s = null;
		Log.e("bla", s+""); // OK 

How to resize an image in ImageView Android source code.
Resize imageview layout and image will resize too:

	public void resizeImageView(int width, int height) {
		final ImageView picture1 = (ImageView)findViewById(R.id.imageView1);
		LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(width, height);
		picture1.setLayoutParams(layoutParams);
	}

Very dark picture, in photo editor black remains black


Very bright picture, in photo editor white will white


Dark picture but the chart is not in black color area - dark shades can be lighten in graphics editor