如何在Android的jar文件中运行课程活动？

Question

I'm new in Android, I've had some problems

I have 2 package:

1. fr.keuse.rightsalert.activity
2. com.example.process

I export the first package into jar file a and then I add to the second package as library. I do like this:

1. I copy the jar file to /libs in the second package
2. I add to build path

the second package import like this:

import fr.keuse.rightsalert.activity.ApplistActivity;

and here is the problem code when I call class in jar file (throwing a Nullpoiterexception

private OnItemClickListener listlistener = new OnItemClickListener() {

    @Override
    public void onItemClick(@SuppressWarnings("rawtypes") AdapterView parent, View arg1, int position,long arg3) {
    //Toast.makeText(getApplicationContext(), "You have clicked on" + position +((Order)parent.getItemAtPosition(position)).getOrderName(), Toast.LENGTH_SHORT).show();

         //------------show new intent when clicked-----------------    
        switch (position){
            case 0:     
                **new fr.keuse.rightsalert.activity.ApplistActivity();
                Intent i = new Intent(System_app.this,ApplistActivity.class);
                startActivity(i);**
                break;

            case 1:
                Toast.makeText(getApplicationContext(), "You have clicked on number 2", Toast.LENGTH_SHORT).show();
                break;
        }   
    }
};

Answer 1

Don't do this:

new fr.keuse.rightsalert.activity.ApplistActivity();

You don't instantiate activities like this. All you need to do to start an activity is this:

Intent i = new Intent(System_app.this,ApplistActivity.class);
startActivity(i);

Android will instantiate the activity for you.

Make sure that you have not defined a constructor for ApplistActivity . Make sure that you have a method onCreate() in ApplistActivity . Make sure that you have this activity listed in your AndroidManifest.xml.