title: Write and Save As with python in plugin QGIS
body: <p>I try to make plugin in QGIS and i want to make save as button but i got error message like this</p>
  
  <pre><code>Traceback (most recent call last):
    File "C:\Users\Mr.Pakde/.qgis2/python/plugins\latih\latihdialog.py", line 69, in 
  
  saveAs
      if not filename.isEmpty():
  AttributeError: 'unicode' object has no attribute 'isEmpty'
  </code></pre>
  
  <p>I write my code like this :</p>
  
  <pre><code>cariButton = self.ui.btnCari
  QtCore.QObject.connect(cariButton,QtCore.SIGNAL('clicked()'),self.cari)
  saveButton = self.ui.btnSave     
  QtCore.QObject.connect(saveButton, QtCore.SIGNAL('clicked()'),self.saveAs)   
  
  def  cari(self, event=None):
      #open dialog
      filename = QtGui.QFileDialog.getOpenFileName(self, 'Open File', '*.xml')         
  
  self.ui.lineFile.setText(filename)
      #panggil isi data
  
  self.isiDataFile(filename)
  
  def isiDataFile(self, nmfile):
          #buka dengan open mode baca
          teksFile = open(nmfile, 'r').read()
  
  self.ui.textFile.setText(teksFile)
  
  def _save(self, filename):        
      f = open( filename, "w" )
          f.write( "%s" % self.lineFile.text() )
  f.close()
  def savefile(self):
       if self.filename:
            self._save( "%s" % self.filename )
  else:
            self.saveAs()
  
  def saveAs(self):
          filename = QtGui.QFileDialog(self).getSaveFileName()
          if not filename.isEmpty():
              _filename = "%s" % filename
              self._save( _filename )
              self.setFilename( _filename )
  </code></pre>
  
  <p>I try to save file in different format</p>