我使用了一个按钮，当你点击这个按钮时，会自动创建一个文本字段并且按钮状态是自动禁用但是如果你点击禁用按钮文本字段是自动删除并且按钮状态被更改为enable.i通过这个过程
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);
}
}
但是，当我运行此代码时，我得到空指针异常，请帮助我在哪里犯错误。
答案 0 :(得分：0)
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.