If condition causing program to force close

Question

I am doing an android app and i was thinking of creating a theme option. Well all I was thinking of doing was to allow the user to click on a image button which represented a theme. And when he clicks on it I start a new activity ie i direct him to the home page. Also i have created a few integer variables which are set to 1 when the user clicks on a button.

Then in the other classes all i do is check if the variables are 1 or not and depending on that i apply the theme. By theme i mean i just change the background wallpaper. But this is not working. I mean the code works but if use an if loop to check the variable values and then apply the effects it causes an error.

Here's the complete code:

package com.example.themetest;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageButton;
import android.widget.LinearLayout;

public class MainActivity extends Activity implements OnClickListener{

    ImageButton ib1;
    ImageButton ib2;
    int water=0;
    int fire=0;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ib1 = (ImageButton) findViewById(R.id.imageButton1);
        ib2 = (ImageButton) findViewById(R.id.imageButton2);
        ib1.setOnClickListener(this);
        ib2.setOnClickListener(this);



    }


    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub

        switch(v.getId()){
        case R.id.imageButton1:
            water = 1;
            Intent wi = new Intent("com.example.themetest.THEME");
            startActivity(wi);
            break;

        case R.id.imageButton2:
            fire = 1;
            Intent fi = new Intent("com.example.themetest.THEME");
            startActivity(fi);
            break;
        }
    }



}

Here's the other class where i check which variable is set to 1 and apply the effect.

package com.example.themetest;

import java.io.InputStream;

import android.app.Activity;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.widget.EditText;
import android.widget.LinearLayout;

public class Theme extends Activity{

    MainActivity main;
    Resources res;
    Drawable drawable;
    LinearLayout linearLayout;




    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.theme);

        if(main.water==1){


            res = getResources(); 
            drawable = res.getDrawable(R.drawable.water_theme); 
            linearLayout =   (LinearLayout)findViewById(R.id.ll); 
            linearLayout.setBackgroundDrawable(drawable);
            }
            else if(main.fire==1){
                res = getResources(); 
                drawable = res.getDrawable(R.drawable.fire_theme); 
                linearLayout =   (LinearLayout)findViewById(R.id.ll); 
                linearLayout.setBackgroundDrawable(drawable);
        }
            else{
                res = getResources(); 
                drawable = res.getDrawable(R.drawable.ic_launcher); 
                linearLayout =   (LinearLayout)findViewById(R.id.ll); 
                linearLayout.setBackgroundDrawable(drawable);
        }

    }



    }

I can change the wallpaper without using the if loop, but i want to do it this way which is not working. Can anyone please tell me why?

Log cat:

01-15 12:08:23.339: D/dalvikvm(273): GC_EXTERNAL_ALLOC freed 767 objects / 55936 bytes in 235ms
01-15 12:08:25.539: D/AndroidRuntime(273): Shutting down VM
01-15 12:08:25.539: W/dalvikvm(273): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
01-15 12:08:25.559: E/AndroidRuntime(273): FATAL EXCEPTION: main
01-15 12:08:25.559: E/AndroidRuntime(273): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.themetest/com.example.themetest.Theme}: java.lang.NullPointerException
01-15 12:08:25.559: E/AndroidRuntime(273):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
01-15 12:08:25.559: E/AndroidRuntime(273):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
01-15 12:08:25.559: E/AndroidRuntime(273):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
01-15 12:08:25.559: E/AndroidRuntime(273):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
01-15 12:08:25.559: E/AndroidRuntime(273):  at android.os.Handler.dispatchMessage(Handler.java:99)
01-15 12:08:25.559: E/AndroidRuntime(273):  at android.os.Looper.loop(Looper.java:123)
01-15 12:08:25.559: E/AndroidRuntime(273):  at android.app.ActivityThread.main(ActivityThread.java:4627)
01-15 12:08:25.559: E/AndroidRuntime(273):  at java.lang.reflect.Method.invokeNative(Native Method)
01-15 12:08:25.559: E/AndroidRuntime(273):  at java.lang.reflect.Method.invoke(Method.java:521)
01-15 12:08:25.559: E/AndroidRuntime(273):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-15 12:08:25.559: E/AndroidRuntime(273):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-15 12:08:25.559: E/AndroidRuntime(273):  at dalvik.system.NativeStart.main(Native Method)
01-15 12:08:25.559: E/AndroidRuntime(273): Caused by: java.lang.NullPointerException
01-15 12:08:25.559: E/AndroidRuntime(273):  at com.example.themetest.Theme.onCreate(Theme.java:29)
01-15 12:08:25.559: E/AndroidRuntime(273):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-15 12:08:25.559: E/AndroidRuntime(273):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
01-15 12:08:25.559: E/AndroidRuntime(273):  ... 11 more
01-15 12:08:31.089: I/Process(273): Sending signal. PID: 273 SIG: 9

Answer 1

I think the better way to do this is pass the name or code of the theme user selected along with the intent.

This might help: Passing data through Intent and receiving it

Answer 2

You cannot access other activities variables this way, a better way (for example) is to use a constant class..

public class Constants {
    public static int water=0;
    public staticint fire=0;
}

MainActivity:

@Override
public void onClick(View v) {
    // TODO Auto-generated method stub

    switch(v.getId()){
    case R.id.imageButton1:
        Constants.water = 1;
        Intent wi = new Intent("com.example.themetest.THEME");
        startActivity(wi);
        break;

    case R.id.imageButton2:
        Constants.fire = 1;
        Intent fi = new Intent("com.example.themetest.THEME");
        startActivity(fi);
        break;
    }
}

Theme:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.theme);

    if(Constants.water==1){


        res = getResources(); 
        drawable = res.getDrawable(R.drawable.water_theme); 
        linearLayout =   (LinearLayout)findViewById(R.id.ll); 
        linearLayout.setBackgroundDrawable(drawable);
        }
        else if(Constants.fire==1){
            res = getResources(); 
            drawable = res.getDrawable(R.drawable.fire_theme); 
            linearLayout =   (LinearLayout)findViewById(R.id.ll); 
            linearLayout.setBackgroundDrawable(drawable);
    }
        else{
            res = getResources(); 
            drawable = res.getDrawable(R.drawable.ic_launcher); 
            linearLayout =   (LinearLayout)findViewById(R.id.ll); 
            linearLayout.setBackgroundDrawable(drawable);
    }

}