我从 String placeName = placeText.getText().toString(); 收到空指针异常

Question

您好，想从编辑文本中获取地名并在地图上标记，这是我的代码，其中出现空指针异常，请帮助我应该做什么以及哪里出错了。

因为我从对话框中的编辑文本字段获取地名。

View layout = View.inflate(this, R.layout.alertbox, null);

            AlertDialog.Builder dialog = new AlertDialog.Builder(this);
            dialog.setTitle("Enter the places");
            dialog.setView(layout);

            dialog.setPositiveButton("Ok", new DialogInterface.OnClickListener() {



                @Override
                public void onClick(DialogInterface dialog, int id) {
                    // TODO Auto-generated method stub


                     EditText placeText = (EditText) findViewById(R.id.strtplace);          
                             String placeName = placeText.getText().toString();
//                              
  Break from execution if the user has not entered anything in the field
                        if(placeName.compareTo("")==0) 
                        numberOptions = 5;
                        String [] optionArray = new String[numberOptions];
                        Geocoder gcoder = new Geocoder(TravellogActivity.this);  

                        try{
                            List<Address> results = gcoder.getFromLocationName(placeName,numberOptions);
                            Iterator<Address> locations = results.iterator();
                            String raw = "\nRaw String:\n";
                            String country;
                            int opCount = 0;
                            while(locations.hasNext()){
                                Address location = locations.next();
                                lat = location.getLatitude();
                                lon = location.getLongitude();
                                country = location.getCountryName();
                                if(country == null) {
                                    country = "";
                                } else {
                                    country =  ", "+country;
                                }
                                raw += location+"\n";
                                optionArray[opCount] = location.getAddressLine(0)+", "+location.getAddressLine(1)+country+"\n";
                                opCount ++;
                            }
                            Log.i("Location-List", raw);
                            Log.i("Location-List","\nOptions:\n");
                            for(int i=0; i<opCount; i++){
                                Log.i("Location-List","("+(i+1)+") "+optionArray[i]);
                            }

                        } catch (IOException e){
                            Log.e("Geocoder", "I/O Failure; is network available?",e);
                        }           

                        p = new GeoPoint(latE6, lonE6);
                        myMC.animateTo(p); 


                    }                       
                });

            dialog.show();
            break;

            }



        return false  ;

    }

Answer 1

NullPointerExceptions 是最容易查找和调试的异常。

如果您在此行遇到 NullPointerException ：

String placeName = placeText.getText().toString();

唯一可以为 null 的是 placeText 变量，或 placeText.getText()

您需要找出原因它为空。由于您的 placeText 处于警报状态，因此您应该使用layout.findViewById 从布局中获取它。当您从错误的位置获取它时，它将为 null，从而导致 NullPointerException。

理论上，getText()也可以返回null，但是Android SDK中当前的实现在没有填写任何内容时会返回一个空字符串，因此不能为null。

Answer 2

使用 EditText placeText = (EditText) layout.findViewById(R.id.strtplace); 而不是 EditText placeText = (EditText) findViewById(R.id.strtplace);

Answer 3

这是您需要做的更改：
//视图和editext都应该声明为final，并且findViewById方法需要一个布局来调用它

• final View布局 = View.inflate(this, R.layout.alertbox, null);
  • final EditText placeText = (EditText)layout.findViewById(R.id.strtplace);