on pressing positive button why dialogbox is closed?

Actually i'm checking some values in my dialog box if they are not valid i don't want to dismiss my dialog box.unfortunately by default When i press submit button my dialog box gets shut down :( how i can escape ???

LayoutInflater factory = LayoutInflater.from(EmailJavaAPI.this);
final View textEntryView = factory.inflate(R.layout.usrpwsdialog,null);
((EditText)textEntryView.findViewById(R.id.etxtUserName)).setText((((EditText)findViewById(R.id.editTextFrom)).getText()).toString());

final EditText usrName = (EditText)textEntryView.findViewById(R.id.etxtUserName);
final EditText usrPws = (EditText)textEntryView.findViewById(R.id.etxtPws);

//AlertDialog alert=new AlertDialog(EmailJavaAPI.this);


return new AlertDialog.Builder(EmailJavaAPI.this)
    .setTitle(R.string.kpsdomain)
    .setView(textEntryView)
    .setPositiveButton(R.string.dgbtnsubmit,
        new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog,
                int whichButton) {
                      userName = usrName.getText().toString().trim();
                      userPws = usrPws.getText().toString().trim();
                      ((EditText)findViewById(R.id.editTextFrom)).setText(userName);

                      if(userName.equals("")){
                              textEntryView.findViewById(R.id.txtVWRUserName).setVisibility(View.VISIBLE);
                      }
                                      if(userPws.equals("")){
                                          textEntryView.findViewById(R.id.txtVWRPws).setVisibility(View.VISIBLE);
                                      }
                                      if(!userName.equals("")&& !userPws.equals("")){
                                          Toast.makeText(EmailJavaAPI.this, "User Name and Password has been set up", Toast.LENGTH_SHORT).show();
                                      }
                                      else{
                                          //***IMPORTANT***
                                          //Dialog Should be opened if this condition is true
                                      }
                                }
                            })
                    .setNegativeButton(R.string.dgbtnDiscard,
                            new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog,
                                        int whichButton) {
                                    dialog.dismiss();
                                }
                            }).create(开发者_JAVA百科);

That's the default behaviour of the alertdialog. You need to customize it like:

@Override
protected Dialog onCreateDialog(int id) {

    LayoutInflater inflator = LayoutInflater.from(context);
    View view = inflator.inflate(R.layout.yourview, null);
    Button positive = (Button)view.findViewById(R.id.btn_positive);
    Button negative = (Button)view.findViewById(R.id.btn_negative);

    positive.setOnClickListener(new Button.OnClickListener(){
        public void onClick(View v) {
            removeDialog(0);
        }
    });

    negative.setOnClickListener(new Button.OnClickListener(){
        public void onClick(View v) {
            removeDialog(0);
        }
    });

    AlertDialog dialog = new AlertDialog.Builder(this).create();
    dialog.setView(view);

    return dialog;
}

It will remove dialog when you will call removeDialog(0).

You can customize your alert like the below.In that you can give your own instruction(Button Action).When you want to close the dialog you have to call

dialog.dismiss();

AlertDialog dialog = new AlertDialog.Builder(context).create();
LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
LinearLayout layout = (LinearLayout) inflater.inflate(R.layout.your_layout, null);
Button btn = (Button) layout .findViewById(R.id.btnid);
btnSet.setOnClickListener(new OnClickListener() {
  @Override
   public void onClick(View v) {
       dialog.dismiss();
       }
    }
    );
dialog.setTitle("Alert Title");
dialog.setView(layout);
dialog.show();