Question

I am use a button and when u click this button a text field is automatic created and button status is automatic disable but if u click on disable button text field is automatic delete and button status is changed to enable.i going through this process.

public class ConfigurationScreen extends MainScreen implements FieldChangeListener{
    TextField tf_text;
    tf_text =  new TextField(TextField.TYPE_PLAIN,img_text[1],img_text[0],TextField.FIELD_HCENTER);
    tf_text.setWidth(Display.getWidth()/2+20);

    ImageButton btn_en;
    btn_en = new ImageButton(imgs_tmintrvl1,"enable",ImageButton.FIELD_HCENTER);

    ImageButton btn_dis;
    btn_dis=new ImageButton(imgs_tmintrvl1,"Disable",ImageButton.FIELD_HCENTER); 

    add(btn_en);

    btn_en.setChangeListener(this);

    public void fieldChanged(Field field, int context) {
        if( field==btn_en)
        {
            delete(btn_en);
            insert(btn_dis, 4);
            insert(tf_text, 5);

            System.out.println(ex);
        }else if (field == btn_dis){
            delete(btn_dis);
            delete(tf_text);
            insert(btn_en, 4);

            System.out.println("Disable Button="+ex);
        }
    }    

But when i run this code i am getting null pointerr exception please help me where i am making mistake.

Answer 1

package org.maxmobility.wmp.beta;

import com.maxmobility.customfield.H_FieldManager;
import com.maxmobility.customfield.ImageButton;
import com.maxmobility.customfield.LabelField;
import com.maxmobility.customfield.PillButtonField;
import com.maxmobility.customfield.PillButtonSet;
import com.maxmobility.customfield.TextArea;
import com.maxmobility.customfield.TextField;
import com.maxmobility.util.AppColors;

import net.rim.device.api.collection.List;
import net.rim.device.api.system.Bitmap;
import net.rim.device.api.system.Display;
import net.rim.device.api.system.EncodedImage;
import net.rim.device.api.ui.Color;
import net.rim.device.api.ui.Field;
import net.rim.device.api.ui.FieldChangeListener;
import net.rim.device.api.ui.FocusChangeListener;
import net.rim.device.api.ui.Font;
import net.rim.device.api.ui.Manager;
import net.rim.device.api.ui.UiApplication;
import net.rim.device.api.ui.container.HorizontalFieldManager;
import net.rim.device.api.ui.container.MainScreen;
import net.rim.device.api.ui.container.VerticalFieldManager;
import net.rim.device.api.ui.decor.Background;
import net.rim.device.api.ui.decor.BackgroundFactory;

public class ConfigurationScreen  extends MainScreen implements FieldChangeListener{

    TextField tf_phn1;
    TextField tf_phn2; 
    TextField tf_msg; 
    TextArea ta_msg;
    ImageButton btn_add;
    ImageButton btn_subtract;
    ImageButton btn_en;
    ImageButton btn_dis;
    ImageButton btn_time1, btn_time2, btn_time3;
    LabelField lf_msg;
    LabelField lf_time;
    LabelField lf1,lf2,lf3,lf4;
    private Bitmap[] imgs_addbtn;
    private Bitmap[] imgs_subbtn;
    private Bitmap[] imgs_tmintrvl1;
    private Bitmap[] imgs_tmintrvl2;
    private Bitmap[] imgs_tmintrvl3;
    private EncodedImage[] img_text;
    private H_FieldManager hfm1 , hfm2;
    private HorizontalFieldManager hfm3,hfm4;
    private VerticalFieldManager vfm;
    private boolean show = false;
    PillButtonField pbf1;
    PillButtonField pbf2;
    PillButtonField pbf3;
    PillButtonSet pbf_set;

    public ConfigurationScreen(){
        super(USE_ALL_HEIGHT | USE_ALL_WIDTH);
        Background background = BackgroundFactory
                .createSolidBackground(AppColors.APP_BG);
        this.getMainManager().setBackground(background);

        LabelField lf = new LabelField("Configuration Screen", LabelField.FIELD_HCENTER | LabelField.USE_ALL_WIDTH);
        lf.setColor(Color.RED);
        setTitle(lf);

         img_text = new EncodedImage[2];
         img_text[0] = EncodedImage.getEncodedImageResource("edittext_selected.png");
         img_text[1] = EncodedImage.getEncodedImageResource("edittext.png");

        imgs_addbtn =  new Bitmap[3];
        imgs_addbtn[0] = Bitmap.getBitmapResource("btn_add_sub.png");
        imgs_addbtn[1] = Bitmap.getBitmapResource("btn_add_subfocused.png");
        imgs_addbtn[2] = Bitmap.getBitmapResource("btn_add_subfocused.png");

        imgs_subbtn =  new Bitmap[3];
        imgs_subbtn[0] = Bitmap.getBitmapResource("btn_add_sub.png");
        imgs_subbtn[1] = Bitmap.getBitmapResource("btn_add_subfocused.png");
        imgs_subbtn[2] = Bitmap.getBitmapResource("btn_add_subfocused.png");

        imgs_tmintrvl1 =  new Bitmap[3];
        imgs_tmintrvl1[0] = Bitmap.getBitmapResource("default_btn_Unfocused.png");
        imgs_tmintrvl1[1] = Bitmap.getBitmapResource("default_btn_focused.png");
        imgs_tmintrvl1[2] = Bitmap.getBitmapResource("default_btn_focused.png");

//        imgs_tmintrvl2 =  new Bitmap[3];
//        imgs_tmintrvl2[0] = Bitmap.getBitmapResource("default_btn_Unfocused.png");
//        imgs_tmintrvl2[1] = Bitmap.getBitmapResource("default_btn_focused.png");
//        imgs_tmintrvl2[2] = Bitmap.getBitmapResource("default_btn_focused.png");
//        
//        imgs_tmintrvl3 =  new Bitmap[3];
//        imgs_tmintrvl3[0] = Bitmap.getBitmapResource("default_btn_Unfocused.png");
//        imgs_tmintrvl3[1] = Bitmap.getBitmapResource("default_btn_focused.png");
//        imgs_tmintrvl3[2] = Bitmap.getBitmapResource("default_btn_focused.png");
//        
        tf_phn1 = new TextField(TextField.TYPE_PHONE,img_text[1],img_text[0],TextField.FIELD_LEFT);
        tf_phn2 = new TextField(TextField.TYPE_PHONE,img_text[1],img_text[0],TextField.FIELD_LEFT);
        tf_msg = new TextField(TextField.TYPE_PLAIN,img_text[1],img_text[0],TextField.FIELD_HCENTER);
        tf_phn1.setWidth(Display.getWidth()/2+50);
        tf_phn2.setWidth(Display.getWidth()/2+50);
        tf_msg.setWidth(Display.getWidth()/2+95);

        ta_msg = new TextArea(Display.getWidth()/2+130, 100,TextArea.FIELD_HCENTER);

         btn_add = new ImageButton(imgs_addbtn," +",ImageButton.FIELD_HCENTER);
         btn_subtract = new ImageButton(imgs_subbtn," -",ImageButton.FIELD_RIGHT);
         btn_en = new ImageButton(imgs_tmintrvl1,"Enable",ImageButton.FIELD_HCENTER);
         btn_dis = new ImageButton(imgs_tmintrvl1,"Disable",ImageButton.FIELD_HCENTER);
//       btn_time1 = new ImageButton(imgs_tmintrvl1, "15 min",ImageButton.FIELD_LEFT);
//       btn_time2 = new ImageButton(imgs_tmintrvl1, "30 min",ImageButton.FIELD_HCENTER);
//       btn_time3 = new ImageButton(imgs_tmintrvl1, "45 min",ImageButton.FIELD_RIGHT);
//       btn_time1.set_Margin(35,0, 0,0);
//       btn_time2.set_Margin(0,0, 0,0);
//       btn_time3.set_Margin(0,0, 0,0);
         //btn_add.set_Margin(0,0, 8,8);
         LabelField lf1 = new LabelField("",Display.getWidth(),45,LabelField.FIELD_LEFT);
         LabelField lf2 = new LabelField("",Display.getWidth(),45,LabelField.FIELD_LEFT);
         LabelField lf3 = new LabelField("",Display.getWidth(),45,LabelField.FIELD_LEFT);
         LabelField lf4 = new LabelField("",Display.getWidth(),45,LabelField.FIELD_LEFT);
         lf_msg = new LabelField("Alert Message",LabelField.FIELD_LEFT);
         lf_msg.set_pos(35,0);
         lf_time = new LabelField("Select Time Interval",LabelField.FIELD_LEFT);
         lf_time.set_pos(35,20);

         pbf1 = new PillButtonField("15 min");
         pbf2 = new PillButtonField("30 min");
         pbf3 = new PillButtonField("45 min");
         pbf_set = new PillButtonSet(300,40);
         pbf_set.add(pbf1);
         pbf_set.add(pbf2);
         pbf_set.add(pbf3);

        hfm1 = new H_FieldManager(tf_phn1, btn_add, true, H_FieldManager.FIELD_HCENTER);
        hfm2 = new H_FieldManager(tf_phn2, btn_subtract, true, H_FieldManager.FIELD_HCENTER);
       // hfm3 = new HorizontalFieldManager(HORIZONTAL_SCROLL_MASK);
        hfm4 = new HorizontalFieldManager(pbf1.FIELD_HCENTER);
//        hfm3.add(btn_time1);
//        hfm3.add(btn_time2);
//        hfm3.add(btn_time3);
        hfm4.add(pbf_set);
        vfm = new VerticalFieldManager();

        add(lf1);
        add(hfm1);
        add(lf_msg);
        //add(tf_msg);
        add(ta_msg);
        add(btn_en);
        add(lf_time);
        //add(hfm3);
        add(hfm4);
        System.out.println(" insert label");


        btn_add.setChangeListener(this);
        btn_subtract.setChangeListener(this);
        btn_en.setChangeListener(this);
        btn_dis.setChangeListener(this);

    }
    public void fieldChanged(Field field, int context) {
        // TODO Auto-generated method stub
        if(field == btn_add){
            insert(hfm2, 2);

        }else if(field == btn_subtract){
            delete(hfm2);
        //}
            }else if(field == btn_en){
                replace(btn_en, btn_dis);

                insert(tf_msg, 5);

            }else if(field == btn_dis){
                replace(btn_dis, btn_en);
                delete(tf_msg);
            }
    }


}

I hope your Problem will solve in this code.