LESSON-10-11_JAVA_EVENTLISTENER.pdf - Android Java File Structure

Overview of the Java File MARY ROSE C. COLUMBRES Bulacan State University - Sarmiento Campus OBJECTIVES: At the end of this lesson, you should be able to: ▪ Discover what is XML and how will you implement this in your application; ▪ Utilize the Java file struct...

Overview of the Java File MARY ROSE C. COLUMBRES Bulacan State University - Sarmiento Campus OBJECTIVES: At the end of this lesson, you should be able to: ▪ Discover what is XML and how will you implement this in your application; ▪ Utilize the Java file structure in android; ▪ Appreciate the importance of “R” or Resources and its methods; and ▪ Utilize the Android Toast. What is Android XML?  XML stands for Extensible Markup Language.  In Cellphone, XML data sent in cellphone that formatted using software designer to display text and images.  XML is a light-weight language that is used for designing layout and it doesn’t make the layout heavy. XML Syntax Rules  XML Syntax Rules  XML Tags is Case Sensitive. All tags need to be written in correct case. XML Syntax Rules  XML must have one root element What is View Elements in XML?  Element is everything that you insert in XML with the start and end tag of the element or simply this is a parent and child of your XML. Elements and View Attributes  Every Element and View has attributes that you can apply to manage the properties of each views. Example What is a Java File?  A Java class file (with the.class filename extension) containing Java bytecode that can be executed on the Java Virtual Machine (JVM).  A Java class file is usually delivered by a Java compiler from Java programming language. UNDERSTANDING THE JAVA FILE STRUCTURE IN ANDROID package com.example.android.myapplication; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } } FindViewById Method private void initializeViews(){ textView = findViewById(R.id.text_view); editText = findViewById(R.id.edit_text); checkBox = findViewById(R.id.check_box); imageView = findViewById(R.id.image_view); } Android Listeners MARY ROSE C. COLUMBRES Bulacan State University - Sarmiento Campus What is an Event Listener?  An event listener is an interface in the View class that contains a single callback method. COMMON CALLBACK METHODS  onClick() - From View.OnClickListener. This is called when the user touches the item (when in touch mode).  onLongClick() - From View.OnLongClickListener. This is called when the user either touches and holds the item (when in touch mode).  onKey() - From View.OnKeyListener. This is called when the user is focused on the item and presses or releases a hardware key on the device.  onTouch() - From View.OnTouchListener. This is called when the user performs an action qualified as a touch event, including a press, a release, or any movement gesture on the screen  onTextChanged() - onTextChangedListener is a method that is called when text is edited or changed inside an EditText What is an Android Toast?  A toast gives straightforward feedback message about an operation in a little popup.  It only fills the amount of space required for the message and the current activity remains visible and interactive.  Toasts naturally vanish after a timeout. What is an Android Toast?  The basic Context context = getApplicationContext(); CharSequence text = "Hello toast!"; int duration = Toast.LENGTH_SHORT; Toast toast = Toast.makeText(context, text, duration); toast.show(); Toast Syntax Toast.makeText(context, "message", duration).show();  Substitute the values: Toast.makeText(MainActivity.this, "Details Saved Successfully.", Toast.LENGTH_SHORT).show(); Positioning your Toast Positioning your Toast  setGravity() method can be used. public void setGravity (int gravity, int xOffset, int yOffset)  Parameters: This method accepts three parameters: Positioning your Toast  gravity: This sets the position of the Toast message.  Following constants can be used to specify the position of a Toast: 1. TOP 2. BOTTOM 3. LEFT 4. RIGHT 5. CENTER 6. CENTER_HORIZONTAL 7. CENTER_VERTICAL Positioning your Toast  xOffset: This is the offset value that tells how much to shift the Toast message horizontally on the x axis.  yOffset: This is the offset value that tells how much to shift the Toast message vertically on the y axis. Positioning your Toast  Example 1. To display the Toast at the center: toast.setGravity(Gravity.CENTER, 0, 0); 2. To display the Toast at the top, centered horizontally: toast.setGravity(Gravity.TOP | Gravity.CENTER_HORIZONTALLY, 0, 0); 3. To display the Toast at the top, centered horizontally, but 30 pixels down from the top: toast.setGravity(Gravity.TOP | Gravity.CENTER_HORIZONTALLY, 0, 30); 4. To display the Toast at the bottom, rightmost horizontally: toast.setGravity(Gravity.BOTTOM | Gravity.RIGHT, 0, 0); Quote of the Day