Wednesday, 17 September 2014

How to turn off notifications for individual android apps?

Background

Notifications form a very important and integral part of Android operating System. They are used to notify user of various actions/updates. A very apt use case is our native email that we configure. Whenever we get a new Email or have a meeting in the calendar scheduled we should get a notification for the same which is what exactly happens. Developers of Android Apps code their app in such a way. 

But here's the problem. We as an end user do not wish to see all notification. For me I am a programmer as well as gamer. I like to try out new Apps including games. Recent ones that I tried include Clash of ClansBoom Beach and Hay Day  But I hate those gaming notifications that pop up. You are in office you get a notification alert. You expect it to be an important mail and it in-fact is some unwanted notification like your life/strength is full again . God.. I hate that moment!



Some developers provide support to disable notifications from the app itself but not all. For example candy crush game provides option to disable notifications - 



Solution


From Android Jelly Bean (4.1) there is support in OS itself for disabling app notification. You can disable any app notification as follows - 

  1. Under each application info screen there is now a checkbox for "show notifications" (assuming the app sends notifications).
  2. Uncheck that and no more notifications from that app should appear in your notification bar.

  3. When you get a notification you don’t want, pull down the notification bar, and hold down the notification until a box pops up that says “App info.” Tap that box. You will see the activity(screen) same as screenshot in step1.



     
Note :  Most apps, especially games, keep updating. When they update they turn the notifications on again. So you may have to repeat this process on each game update.

I have tested with my apps and it seems to work fine. Do share your experiences with unwanted notifications and if you tried any other method (other than rating it 1 star and uninstalling it :) ).

In older versions of Android than Jelly bean you are really at the mercy of programmer hoping that he/she has provided notification option in the settings.

Sunday, 14 September 2014

Difference between block level elements and inline elements in HTML

Background

Most of you might already know HTML stands for HyperText Markup Language and is the standard markup language used to create web pages. HTML consists of elements. Most of the elements have stating and ending tag. For eg. <div></div>. Some don't need. For eg. <br />. You can read more about it on Wikipedia or w3schools. In this post I am going to cover what are basic blocks in a HTML.

Blocks in HTML

Elements in HTML are categorized into two types- 
  1. block level elements
  2. inline elements

When block level elements are rendered in a webpage they generally begin and end with a new line. For example <ul>, <table>, <h1>, <p>  tags. Inline elements comprise of tags that come inside(nested) block level element tags. For example <a>, <img>, <b>, <td>.

Difference

Picking this up directly from the W3 documentation -

Certain HTML elements that may appear in BODY are said to be "block-level" while others are "inline" (also known as "text level"). The distinction is founded on several notions:

  • Content model : Generally, block-level elements may contain inline elements and other block-level elements (Exception to this on paragraph/p tag). Generally, inline elements may contain only data and other inline elements. Inherent in this structural distinction is the idea that block elements create "larger" structures than inline elements.
  • Formatting : By default, block-level elements are formatted differently than inline elements. Generally, block-level elements begin on new lines, inline elements do not.

Below are some details on <div> and <span> elements which I have directly picked up from W3schools.I have used them a lot in web pages and JSPs but never knew the basic difference between them and their intended purpose.

<div>  element

  • The HTML <div> element is a block level element that can be used as a container for grouping other HTML elements.
  • The <div> element has no special meaning. Except that, because it is a block level element, the browser will display a line break before and after it.
  • When used together with CSS, the <div> element can be used to set style attributes to large blocks of content.
  • Another common use of the <div> element, is for document layout. It replaces the "old way" of defining layout using tables. Using <table> elements for layout is not the correct use of <table>. The purpose of the <table> element is to display tabular data.

<span> element

  • The HTML <span> element is an inline element that can be used as a container for text.
  • The <span> element has no special meaning.
  • When used together with CSS, the <span> element can be used to set style attributes to parts of the text.


Nesting block level elements inside the <p> tag… right or wrong?

As the documentation clearly says

The P element represents a paragraph. It cannot contain block-level elements (including P itself).

You cannot use block level elements inside paragraph tag. Well no body stops you from adding it but here's what will happen  - opening <div> or any other block level tag will automatically close the <p> element.

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Saturday, 13 September 2014

Method overloading in Javascript

Background on method overloading

If you are from java or C# background then you must be familiar with the concept of method overloading. You can refer to following post on method overloading in java


Just to summarize (as far as java is considered) two methods are said to be overloaded if they have same method name but different method signatures. Also note method signature is the name of the method plus the number and types of arguments. Signature has nothing to do with return type. Also two methods cannot have same signature.

So for example

public void foo(String arg1);
public void foo(String arg1, String arg2);

are overloaded methods. Also note method overloading is a compile time phenomenon. Which method is to be used for execution is decided at compile time depending on the method signature.

Okay enough of Java overloading background. Lets head to javascript.



Method overloading in Javascript

Method overloading is not possible in Javascript in strict sense!

yeah that's right. You should not do something like

function foo(x)
{
  //some logic 
}

function foo(x,y)
{
  //some logic 
}

Why have i written "should not" rather than "cannot" is because no body can stop you from writing the methods above. It's just that it will not serve it's intended purpose. Why not ?-

The issue is that JavaScript does NOT natively support method overloading. So, if it sees/parses two or more functions with a same names it’ll just consider the last defined function and overwrite the previous ones.

So  foo(x,y) wold override foo(x) in above case.  So if I call method as foo(1) and as per what I have written above foo(x,y) will overwrite foo(x) why is there no some kind of error or Exception ? 

Well because when you specify arguments in the round brackets - they are just like synthetic sugar coating on the real arguments. This is where there is another JavaScript feature, which a lot beginners miss out on. In any JavaScript method, the arguments passed into the method are accessible via an Object array with the name arguments.

So lets say you now have a method

function func1(a,b,c)
{

   //some logic 
} 

and you call func1(1,2,3,4) then a=1(arguments[0]), b=2(arguments[1]),c=3(arguments[2]) and you c(arguments[3]). So as I said arguments inside round brackets are just to improve the functionality.


In fact for above method you can also call it like func1(1,2) and in this case arguments c and d will be undefined. Following the same argument above you can have a function defined with no argument and call it with any number of arguments.

You can check any variable if it is undefined in the following way (using typeof ) -


function func1(a,b,c,d)
{
   if(typeof a == 'undefined')
   {
      alert("a is undefined"); 
    }
     // and so on... 
}


So how do we resolve this issue ?

One of the way I think is suitable for most of the case is follows -

Lets say you have method

function foo(x)
{

} 


Instead of overloading method which is not possible in javascript you can define a new method

fooNew(x,y,z)
{
}


and then modify the 1st function as follows -

function foo(x)
{
  if(arguments.length==2)
  {
     return fooNew(arguments[0],  arguments[1]);
  }
} 

If you have many such overloaded method consider using switch than just if-else statements.

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Monday, 8 September 2014

Lifecycle of SimpleFormController of Spring MVC

Background

Yes SimpleFormController has been deprecated since Spring 3.0 but is still widely used. So  in this post I am going to discuss the lifecycle or workflow of this controller.

Steps

Workflow is as follows and it is controlled by AbstractFormController class - 

  1. The controller receives a request for a new form (typically a GET).
  2. Call to formBackingObject() which by default, returns an instance of the commandClass that has been configured (see the properties the superclass exposes), but can also be overridden to e.g. retrieve an object from the database (that needs to be modified using the form).
  3. Call to initBinder() which allows you to register custom editors for certain fields (often properties of non-primitive or non-String types) of the command class. This will render appropriate Strings for those property values, e.g. locale-specific date strings.
  4. Only if bindOnNewForm is set to true, then ServletRequestDataBinder gets applied to populate the new form object with initial request parameters and the onBindOnNewForm(HttpServletRequest, Object, BindException) callback method is called. Note: any defined Validators are not applied at this point, to allow partial binding. However be aware that any Binder customizations applied via initBinder() (such as DataBinder.setRequiredFields(String[]) will still apply. As such, if using bindOnNewForm=true and initBinder() customizations are used to validate fields instead of using Validators, in the case that only some fields will be populated for the new form, there will potentially be some bind errors for missing fields in the errors object. Any view (JSP, etc.) that displays binder errors needs to be intelligent and for this case take into account whether it is displaying the initial form view or subsequent post results, skipping error display for the former.
  5. Call to showForm() to return a View that should be rendered (typically the view that renders the form). This method has to be implemented in subclasses.
  6. The showForm() implementation will call referenceData(), which you can implement to provide any relevant reference data you might need when editing a form (e.g. a List of Locale objects you're going to let the user select one from).
  7. Model gets exposed and view gets rendered, to let the user fill in the form.
  8. The controller receives a form submission (typically a POST). To use a different way of detecting a form submission, override the isFormSubmission method.
  9. If sessionForm is not set, formBackingObject() is called to retrieve a form object. Otherwise, the controller tries to find the command object which is already bound in the session. If it cannot find the object, it does a call to handleInvalidSubmit which - by default - tries to create a new form object and resubmit the form.
  10. The ServletRequestDataBinder gets applied to populate the form object with current request parameters.
  11. Call to onBind(HttpServletRequest, Object, Errors) which allows you to do custom processing after binding but before validation (e.g. to manually bind request parameters to bean properties, to be seen by the Validator).
  12. If validateOnBinding is set, a registered Validator will be invoked. The Validator will check the form object properties, and register corresponding errors via the given Errors object.
  13. Call to onBindAndValidate() which allows you to do custom processing after binding and validation (e.g. to manually bind request parameters, and to validate them outside a Validator).
  14. Call processFormSubmission() to process the submission, with or without binding errors. This method has to be implemented in subclasses.


Above was the workflow  as specified in the Spring documentation of AbstractFormController. 

If it's confusing refer to following diagrammatic representations and try to co-relate

Diagrammatic Representation



Note :  If there are any errors in command object fields binding form will be reloaded (as shown in Request 2 of above diagram and after processFormSubmission(), showForm() and referenceData() are again called). onSubmit() is never called if this happens.

Typically a Spring bean lifecycle of a SimpleFormController would look something like below - 



Understanding some basic methods

  • isFormSubmission() : This method determines whether form is submitted (a POST request) or is for initial viewing (a GET request). This method is the base on which the two workflows of SimpleFormController are split.
  • formBackingObject() : This method returns an instance of command object which is the form Object. You can specify the class of this Object by setCommandClass( ) method. Or you can directly specify it in your bean configuration file -

    <property name="commandClass">
    <value>org.opensourceForgeeks.FormBackingObject</value>
    </property>

  • initBinder() : This method is called after the form command object is created and data binder is created by the controller. Developers can override this method to register custom PropertyEditor.
  • isValidateOnBinding(): If this method returns true then the binding validations are performed. By default it is set to true and final. Only way to change it is through setValidateOnBinding() method.
  • referenceData(): This method is used to provide reference data if any. Do not confuse it with formBackingObject() method where form Object is created. This method is used to provide any extra reference data that model may need to render UI page other that the command object. Whole model is then sent  to the View set by formView property of the bean in dispacher-servlet.xml file. Form View will then be rendered (See above diagrams for reference).

Related Links

Tuesday, 2 September 2014

Calling JavaScript function in href vs. onclick

Background

There are multiple ways to call a Javscript function in an anchor tag. You can put the method in href attribute or you can use onclick event or jquery events. This post is about good practices while calling a javascript function in such a scenario.


Usage in order of  increasing good practice


<a id="myLink" href="javascript:MyFunction();">link text</a>
 
<a id="myLink" href="#" onclick="MyFunction();">link text</a>
 
<a id="myLink" href="#" onclick="MyFunction();return false;">link text</a>
 
<a id="myLink" title="Click to do something" href="#" onclick="MyFunction();return false;">link text</a>
 
<a id="myLink" title="Click to do something" href="PleaseEnableJavascript.html" onclick="MyFunction();return false;">link text</a>

But the best practice as of now is to use jquery and attach an even handler to the elements id. Something like -

$('#myLink').click(function()

  {

     MyFunction();

     return false;

  }); 

 Notes

  • The onclick won't fire if someone middle-clicks on your link to open a new tab or if they have JavaScript disabled.
  • In case javascript is enabled adding return false in  onclick will will prevent browser from following the link.
  •  If you don't have a link in href attribute you should do javascript:void(0) rather than # in the href attribute.  '#' will take the user back to the top of the page if it is present in the href attribute and onclick is not returning false.

 

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