SL4A - Building GUIs


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A Graphical User Interface (GUI) represents a set of graphical components that enables the user to browse, access and interact with the application functionalities.

There are two basic approaches to user interaction with SL4A namely −

  • Dialog boxes such as Alerts.

  • Using HTML and JavaScript to build the UI and then Python behind the scenes to handle any additional processing.

This chapter explains both the approaches.

Python Dialog Box – Based GUIs

SL4A includes a UI façade to access the basic UI elements provided by the android API. These functions return a result object as a named tuple when called. Each result is assigned a unique id for tracking purpose. The second element is the result. It represents the user’s input. The tuple also includes the third element error to provide feedback to the caller about any error condition that might have been encountered. If no errors were encountered this element is set to None.

S.No. UiFacade Function & Description
1

dialogGetInput

Queries the user for a text input.

title (String) title of the input box (default = Value)

message (String) message to display above the input box (default = Please enter value:)

defaultText (String) text to insert into the input box (optional)

The result is the user's input, or None (null) if cancel was hit.

2

dialogShow

Show dialog

3

dialogCreateAlert

Create alert dialog.

title (String)(optional)

message (String) (optional)

4

dialogDismiss

Dismiss dialog.

5

dialogCreateDatePicker

Create date picker dialog.

year (Integer) (default = 1970)

month (Integer) (default = 1)

day (Integer) (default = 1)

6

dialogCreateTimePicker

Create time picker dialog.

hour (Integer) (default = 0)

minute (Integer) (default = 0)

is24hour (Boolean) Use 24 hour clock (default = false)

7

dialogGetPassword

Queries the user for a password.

title (String) title of the password box (default = Password)

message (String) message to display above the input box (default = Please enter password:)

8

dialogGetResponse

Returns dialog response.

9

dialogSetPositiveButtonText

Set alert dialog positive button text. text (String)

10

dialogSetNegativeButtonText

Set alert dialog button text. text (String)

11

dialogSetNeutralButtonText

Set alert dialog button text. text (String)

12

dialogSetSingleChoiceItems

This creates a list of radio buttons.

13

dialogSetMultiChoiceItems

This creates a checkbox

14

dialogCreateHorizontalProgress

Create a horizontal progress dialog.

title (String) (optional)

message (String) (optional)

maximum progress (Integer) (default = 100)

15

dialogCreateSpinnerProgress

Create a spinner progress dialog.

title (String) (optional)

message (String) (optional)

maximum progress (Integer) (default = 100)

16

addContexMenuItem

Adds a new item to context menu.

label (String) label for this menu item

event (String) event that will be generated on menu item click

eventData (Object) (optional)

17

addOptionsMenuItem

Adds a new item to options menu.

label (String) label for this menu item

event (String) event that will be generated on menu item click

eventData (Object) (optional)

iconName (String)

18

webViewShow

Display a WebView with the given URL.

url (String)

wait (Boolean) block until the user exits the WebView (optional)

19

clearContextMenu

Removes all items previously added to context menu.

20

clearOptionsMenu

Removes all items previously added to options menu

21

makeToast

Create a notification

Examples

A simple Toast Example

import android 
droid = android.Android() 
uname = droid.getInput("Enter your name") 
print uname  
droid.makeToast("Hello %s" %uname.result)

A Horizontal Progress Bar

import android 
   droid = android.Android() 
   title = "Progress" 
   str = "Loading..." 
   droid.dialogCreateHorizontalProgress(title,str,100) 
   droid.showDialog() 
	
   for x in range(0,99) 
      time.sleep(0.1) 
      droid.dialogSetCurrentProgress(x) 
		
   droid.dialogDismiss()

Modal Vs Non-Modal Dialog Boxes

A modal dialog box or window is a child to another process or window. With a modal dialog box, processing will wait or block until the user interacts with the new dialog box.

A typical example of this case is an alert dialog box. The alert will not close until the user performs an action.

The following image is an example of a modal dialog box.

Modal Dialog Box

To sum up, use a modal dialog box when you need input from the user before you continue execution.

Python GUIs with HTML

SL4A enables building Graphical User Interfaces (GUIs) based on CSS, HTML, JavaScript and Python. The approach uses HTML and JavaScript to build the UI, CSS to enhance the appearance and consistency of HTML elements and fonts and Python to handle any additional processing.

The following example illustrates a basic HTML GUI example −

1. Speech.html

<html> 
   <head> 
      <title>Text To Speech</title> 
		
      <script> 
         var droid = new Android(); 
         var speak = function(){ 
            droid.postEvent("say",document.getElementById("say").value); 
         } 
      </script> 
		
   </head>
	
   <body> 
      <form onsubmit = "speak()";return false;”> 
         <label for = "say">What is your message?</label> 
         <input type = "text" id = "say"/> 
         <input type = "submit" value = "Speak"/> 
      </form> 
   </body> 
	
</html>

2. txtToSpeech.py

import android 
droid = android.Android() 
droid.webViewShow(‘file:///sdcard/sl4a/scripts/Speech.html’) 

while True: 
   result = droid.waitForEvent(‘say’).result 
   droid.ttsSpeak(result[‘data’])

Both the files − Speech.html and txtToSpeech.py, must reside in the /sdcard/sl4a/scripts directory on the device. Run the python script to launch the HTML file.

This file is launched by the webViewShow API call. The event is generated when the Speak button is clicked.



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