Event Handling

What are events? Why do we need to handle them? Events occur when an user interact with the UI components of our app like buttons. When these events occurs, a function/method is called. As a programmer, it is our responsibility to dump a block of code inside that method/function and make the UI respond to the user, like closing the application when the user presses the "quit" button. Seems like a good idea. Lets do just that.


Create a project. First, we need to include a button in our layout and id it. I do the same in the following code:




In our source code ( java file ), we need to add a variable for this button and add a listener to it, which is done in the following code:


This can also be done another way. Instead of adding OnClickListener on the java file, we can handle events by addding the tag android:onClick="myOnClickMethod". "myOnClickMethod" is a method defined inside our activity class(java file). Any name can be given to the method but it must have an argument of type "View". Take a look at my button in layout and the method myOnClickMethod() in my activity class:

A code snippet for button:






The Activity:


These methods are enough to implement event listeners for 2 or 3 buttons. But what if we need to handle the events of 10 buttons. For this situation, there is a special way of implementing listeners. Lets say we have 4 buttons and a text view as in the layout below. We need to print the event occurred like printing "Button 1 is pressed" when button1 is pressed. What we do is that, we make our activity to implement a class "View.OnClickListener" and then, we implement the common method onClick(), in which we differentiate events occurred by using id of the buttons. This is done in the code given below.


main.xml




BaseActivity.java

Some snaps:


1. The quit button:

2. Button2 event:

3. Button4 event:

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OK... thats it for now guys!!! See ya later with more.....

Building an Image Editor 1

This post is made to help/support the members of the ADI community who are attending the event Image Editor for Android. The event description is as follows:

Yeah! We are gonna do it step by step. As Step1, we'll try to create an Image Viewer app. The app will call the default inbuilt camera application which lets us capture a pic and then shows the pic in the base/home screen of our app. thats it. simple right?... Lets make an outline of our app.





So, how exactly do we access the default camera application? We'll use an intent to trigger it using the parameter "android.provider.MediaStore.ACTION_IMAGE_CAPTURE". An activity is started with this intent. When this activity ends, the image associated with the intent is obtained. This image is set to the ImageView already created in our layout and displayed in our base screen. We'll start the activity by using StartActivityForResult() method, so that we can fetch the image from the resulting intent. Thats enough about it, lets jump to the code. The layout file consists of just an ImageView component and is embedded below:





Now lets look at our Activity:







Check out some of the snaps below:


1. The problem with AVD:

* Note: Click on the picture to view in high resolution.


2. Camera doesn't seem to work:

* Note: Click on the picture to view in high resolution.




3. When uploaded and started in my phone:

------------> Download Project here <---------------




There are a number of problems in this app like, the picture captured is not saved anywhere, there are no buttons for capturing, no quit button and the image displayed is just a thumbnail of the image captured (low resolution). In the next post, we'll try to capture an image, save it anywhere we want, access it using the file path and we do all this using buttons. Thats it for now. See ya!!!!.....