Unzip files in Android

You need an app that can unzip files? Android provides the classes that are required for this. Basically you will need to checkout two classes. There are other related classes also which would help you with various other things.

1. ZipInputStream
2. ZipEntry

This example shows you how to unzip a zip file through these classes. If you want to create zip files, that's also possible, but we will keep it for later. In this project, there is a zip file, called ZipTest.zip in the assets folder. It's pretty easy to pick up any zip file on your phone through code. For simplicity, I have placed out test file in the assets folder.

The code is simple enough to need any more explanations. I have put comments in the code. So, do check it out and run it. I have logged the steps on the Activity. The output files are not readable yet in this example due to the format of writing that I have done here (Update: As per rekin's comment, this is fixed now). But you get idea about how to unzip those files. You can find the whole working code here.

Note: There's not much error handling code put in place.

Android WebView, Javascript and CSS

Using WebViews on Android is pretty interesting. I have come across some situations where I had to use a WebView to display some HTML content. Displaying HTML content is pretty straight-forward. But when it comes to controlling the web view, it gets a little complex. Things like showing alerts, manipulating divs and controlling the activity (closing/finishing). This example shows a few techniques that will get you going with Javascript and CSS with WebView.

1. CSS: Applying CSS is just the same as you would do with normal HTML pages. The sample_page.html in the assets folder refers to the sample_style.css file in the same folder. One thing you might notice is how we get the rounder corners for the divs. This CSS attribute does the trick.

             -webkit-border-radius: 5px;

2. Javascript: To make it simpler, I have used the JQuery library. The mobile version released recently gave some errors. So, I have used the normal library available. The jquery-1.4.2.min.js also resides in the assets folder and is referenced in the sample_page.html.

3. All together: In the sample_page.html I have a header, a body and the controls. The controls have four buttons
      a: JToggle: This toggles the visibility of the body section. This is a pure javascript method call from the html.
      b: NToggle: This also toggles the visibility of the body section. But it does it differently. The javascript calls to the JSInterface.java method, which in turn calls the same Javascript method.
      c. Exit: This button basically closes/exits the app, by calling the JSInterface.java method which is bound to the HomeActivity.java via OnExitAppListener.java
      d. Alert: This shows an alert which is basically an AlertDialog in Android.

Calling a Javascript method from your Java code:
webView.loadUrl("javascript:jsToggle()");

Calling a Java method from Javascript:
window.jsinterface.nativeToggle();
/*
  // Before using the above code, you have to inject the interface object which
  // has a name "jsinterface"
  webView.addJavascriptInterface(jsInterface, "jsinterface");
*/

Controlling the Alerts from Javascript:
The SampleChromeClient.java which extends the WebChromeClient has several methods which provide hooks which allow you to customize their behaviour. For an example, you can override the behaviour of the alert function and do whatever you want. You can show your own dialog with Yes/No buttons and depending on the input, you can send back the result to your Javascript code.
 @Override
 public boolean onJsAlert(WebView view, String url, String message, JsResult result)
 {
     url = "Sample App Alert";
     return super.onJsAlert(view, url, message, result);
 }
You can checkout the whole source code here. It's ready to run. Let me know if you have any issues.

More security for your Android

Android has been criticized by a few of not having stricter security policies, on which a user could count on if his device is lost or stolen. Since more and more data, both personal and confidential are finding there way into our smart phones, we do need a more secure system to ensure that our data never fall into the wrong hands. Well, with Android 2.2(Froyo), your Android phones can be more secure by using the new Device Administration API.

What could this API do?
Using these APIs, the IT-Admins can install a Admin App, which enforces system wide security policies.

- Enable Passwords (Only lock screen as of now)
- Set minimum password length
- Alphanumeric password required
- Maximum password attempts
- Maximum inactivity time lock
- Lock device immediately
- Wipe the device data (to factory settings) (Remote/Local)

The key to all these features are that you have to have that admin app installed and activated as well. Also, you can have multiple admin apps that enforce multiple security policies. In situations of clash, the most strict policy will be enforced. This admin app controls how your device behaves in different situations. You can set parameters as to when and under what conditions your device should be wiped out. Say, after 20 failed password attempts, you want to wipe out the data to factory settings, the Admin app can do this using the Device Administration API.

For more information and samples on how to start with this API, visit the official documentation here.

With more and more features being packed into Android, now it is probably targeting the enterprises. Not having a way of enforcing such policies have indeed been a setback for Android to entice the Business users, but now, I can hear them come running. :D

ExpandableListView on Android

ListView is pretty widely used. There are situations when you would like to group/categorize your list items. To achieve such a thing on Android, you would probably use the ExpandableListView. The data to the ExpandableListView is supplied by a special kind of adapter called the SimpleExpandableListAdapter which extends the BaseExpandableListAdapter.

As with any other widget on Android, you are free to customize the widgets as per your needs. Here, I will show how to create such a custom list adapter for the ExpandableListView.

For this example, I want to show a list of vehicles with their names. Also, I want to group them according to their category.

I have 4 classes.
1. Vehicle : The parent class for the rest.
2. Car: Extends the Vehicle class.
3. Bus: Extends the Vehicle class.
4. Bike: Extends the Vehicle class.

I have a method called getRandomVehicle(String name) which returns a random vehicle instance setting the name that I pass. The vehicle can be a Bus, Car or a Bike. Its completely random.

In the ExpandableListAdapter, (the custom adapter), there's a method called addItem(Vehicle vehicle), which manages the groups and their children.

In the SampleActivity, I have initialized a blank ExpandableListAdapter and set it to the list view. Now, I start a thread, which gets a random vehicle after every 2 seconds, and adds it to the adapter, and calls the adapter to notify that the data has changed.

There are a few methods, in the ExpandableListAdapter, which you should go through carefully. I have two layout files, group_layout.xml and child_layout.xml which are used as the layout for the group views and the child views of the ExpandableListView.

There you go, you have a custom ExpandableListView. You can find the full source code for this example here, ready to run.

There are some more methods that you might be interested in, like, how to change the "arrow icon" for the group views(official doc link), or how to expand or collapse a group at will, or how to handle specific events like group collapsed or group expanded. Read the docs on ExpandableListView.

SDK Tools - ADT Plugin updated

Here comes a new update to the ADT plugin for eclipse and SDK tools.

After you update the SDK tools(r7) from the Android SDK manager or otherwise, you would be prompted to update the ADT plugin(0.9.8) as well. Go for it, and you will see quite a few changes.

In the SDK Tools:
http://developer.android.com/sdk/tools-notes.html 

In the ADT Plugin:
http://developer.android.com/sdk/eclipse-adt.html

For SDK Tools
- Support for library projects.
- Support for aidl files in library projects
- Support for extension targets in Ant build to perform tasks between the normal tasks
- Support for "headless" SDK update 
- Fixes location control in DDMS to work in any locale not using '.' as a decimal point

For ADT Plugin
- Rename package : One click change of project's package
- Support for library projects that don't have a source folder called src/
- Support for library projects that depend on other library projects
- Support for additional resource qualifiers: car/desk, night/notnight and navexposed/navhidden
- Adds more device screen types in the layout editor. (Nice)
- Fixes problems with handling of library project names

The most important update for me is the inclusion of more layout editor configurations by default. My last post on creating different configurations for different screen sizes here was just an example to create a configuration for working with different screen sizes at design time. It's a bonus that they are now included in there by default.

Once click package renaming is also a nice feature, in case you want to fork your project into different versions. Check them out.