ListView item set error Android

问题

I have a listview that have 5 item in it if am trying to set error on the 4 th and 5th item .Then it is throwing a null pointer exception. Exception

08-22 13:34:49.523: E/AndroidRuntime(16952): FATAL EXCEPTION: main
08-22 13:34:49.523: E/AndroidRuntime(16952): java.lang.NullPointerException
08-22 13:34:49.523: E/AndroidRuntime(16952):    at com.example.iweenflightbookingpage.MainActivity$1.onClick(MainActivity.java:116)
08-22 13:34:49.523: E/AndroidRuntime(16952):    at android.view.View.performClick(View.java:4091)
08-22 13:34:49.523: E/AndroidRuntime(16952):    at android.view.View$PerformClick.run(View.java:17072)
08-22 13:34:49.523: E/AndroidRuntime(16952):    at android.os.Handler.handleCallback(Handler.java:615)
08-22 13:34:49.523: E/AndroidRuntime(16952):    at android.os.Handler.dispatchMessage(Handler.java:92)
08-22 13:34:49.523: E/AndroidRuntime(16952):    at android.os.Looper.loop(Looper.java:153)
08-22 13:34:49.523: E/AndroidRuntime(16952):    at android.app.ActivityThread.main(ActivityThread.java:4987)
08-22 13:34:49.523: E/AndroidRuntime(16952):    at java.lang.reflect.Method.invokeNative(Native Method)
08-22 13:34:49.523: E/AndroidRuntime(16952):    at java.lang.reflect.Method.invoke(Method.java:511)
08-22 13:34:49.523: E/AndroidRuntime(16952):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:821)
08-22 13:34:49.523: E/AndroidRuntime(16952):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:584)
08-22 13:34:49.523: E/AndroidRuntime(16952):    at dalvik.system.NativeStart.main(Native Method)

Code To set Error

click.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View arg0) {
   allValues = myAdapter.getAllValues();
                ArrayList<Integer> errorList = new ArrayList<Integer>();
                for(int i = 0; i < allValues.length; i++){
                   for(int j=0;j<staticPasengerList.length;j++){
                       if(allValues[i] == staticPasengerList[j]){
                            Log.d("Lop Count", ""+allValues[i]+"="+staticPasengerList[j]);

                            // Add position to errorList
                            errorList.add(i);
                        }
                   }

                }
                 myAdapter.setErrorList(errorList);
                 myAdapter.notifyDataSetChanged();
          }

        }
    }

BaseAdapter Class

class data extends BaseAdapter {
    String[] Title;
    Activity activity;

    public data (MainActivity mainActivity, String[] text) {
        Title = text;
        activity = mainActivity;
    }

    public String[] getAllValues() {
        return Title;
    }

    public int getCount() {
        // TODO Auto-generated method stub
        return Title.length;
    }

    public Object getItem(int arg0) {
        // TODO Auto-generated method stub
        return null;
    }

    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = activity.getLayoutInflater();
        View row ;
        row = inflater.inflate(android.R.layout.simple_list_item_1, parent, false);
        TextView title;
        title = (TextView) row.findViewById(android.R.id.text1);
        title.setText(Title[position]);
        return (row);
    }

This exception is occuring in case of 4 and 5 will be the value of i. Please help me to resolve the issue

回答1:

The following should solve your problem. Please read the comments for explanation:

class data extends BaseAdapter {
    String[] Title;
    Activity activity;
    ArrayList<Integer> errorPositionList;

    public data (MainActivity mainActivity, String[] text) {
        Title = text;
        activity = mainActivity;
        errorPositionList = new ArrayList<Integer>();
    }

    // Add this method
    public void setErrorList(ArrayList<Integer> eList) {
        errorPositionList = eList;
    }

    ....
    ....

    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = activity.getLayoutInflater();
        View row ;
        row = inflater.inflate(android.R.layout.simple_list_item_1, parent, false);
        TextView title;
        title = (TextView) row.findViewById(android.R.id.text1);

        if (errorPositionList.contains(position)) {
            title.setText(Title[position]);
            title.setError("Please change the data");
        } else {
            title.setText(Title[position]);
        }

        return (row);
    } 
}

And the OnClickListener should now look like:

click.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View arg0) {
        allValues = myAdapter.getAllValues();
        Log.d("this is my array", "arr: " + Arrays.toString(allValues));

        // Declare and initiate the ArrayList
        ArrayList<Integer> errorList = new ArrayList<Integer>();

        for(int i = 0; i < allValues.length; i++){
            if(allValues[i] == passengerList[i]){
                Log.d("Lop Count", ""+allValues[i]+"="+i);

                // Add position to errorList
                errorList.add(i);
            }
        }         

        myAdapter = new PassengerListView(MainActivity.this, allValues);
        listView.setAdapter(myAdapter);

        // Use setErrorList(ArrayList<Integer> eList) method from adapter
        myAdapter.setErrorList(errorList);

        // Update the list
        // The if statement inside getView() will set the error message
        myAdapter.notifyDataSetChanged();
    }
}

Update:

OP will need to implement error notification. Relying on setError(CharSequence) will not work in this case.

回答2:

You should consider that getChildAt(4) may return null .

you can setError() in your adapter's method getView() where position will be 4 . . .

EDITED:

class data extends BaseAdapter {
    String [] passengersList;
    String[] Title;
    Activity activity;

    public data (MainActivity mainActivity, String[] text, String[] passengersList) {
        Title = text;
        activity = mainActivity;
        this.passengersList = passengersList;
    }

    public String[] getAllValues() {
        return Title;
    }

    public int getCount() {
        // TODO Auto-generated method stub
        return Title.length;
    }

    public Object getItem(int arg0) {
        // TODO Auto-generated method stub
        return null;
    }

    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = activity.getLayoutInflater();
        View row ;
        row = inflater.inflate(android.R.layout.simple_list_item_1, parent, false);
        TextView title;
        title = (TextView) row.findViewById(android.R.id.text1);
        if(position == 4){
           checkAndSetError(title);
        }
        title.setText(Title[position]);
        return (row);
    }

    private void checkAndSetError(TextView title, int position){
        allValues = this.Title;
        Log.d("this is my array", "arr: " + Arrays.toString(allValues));
        for(int i=0;i<allValues.length;i++){
           if(allValues[position] == this.passengerList[i]){
               Log.d("Lop Count", ""+allValues[i]+"="+i);
               title.setError("Please change the data");
          }
        }
    }
}

It Should look something like this.

回答3:

ListView component did not render element on position 4. It is a lazy component that renders only what is on screen. So don't assume that getChildAt returns a non null view.

Tell your adapter to show error at position 4 and let ListView know that data set changed by calling notifyDataSetChanged.

Extend your adapter with list of position, where to show error.
On click, add position to that list.
Call notifyDataSetChanged from adapter.
Change getView method to show error if it is rendering a view with error.

来源：https://stackoverflow.com/questions/18374921/listview-item-set-error-android

标签

android

android-listview