Designing Your User interface Using Views

Designing Your User interface Using Views:
                                                                               "In Android UI consists of view the viewGroups are divided into following categories."

➤➤ Basic views — Commonly used views such as the TextView, EditText, and Button
views

➤➤ Picker views — Views that enable users to select from a list, such as the TimePicker
and DatePicker views

➤➤ List views — Views that display a long list of items, such as the ListView and the
SpinnerView views

BASIC VIEWS:

                       "The basic views enable you to display text information, as well as perform some basic selection.To get started, let’s explore some of the basic views that you can use to design the UI of your Android applications:"

➤➤ TextView

➤➤ EditText

➤➤ Button

➤➤ ImageButton

➤➤ CheckBox

➤➤ ToggleButton

➤➤ RadioButton

➤➤ RadioGroup

The following sections explore all these views in more detail.

TextView view :"The TextView view is used to display text to the user. This is the most basic view and one that you will frequently use when you develop Android applications. If you need to allow users to edit the text displayed, you should use the subclass of TextView, EditText, which is discussed in the next section."

When you create a new Android project, Eclipse always creates the main.xml fi le (located in the res/

layout folder), which contains a <TextView> element:

exj-

   <?xml version=”1.0” encoding=”utf-8”?>

    <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android”

      android:orientation=”vertical”

      android:layout_width=”fill_parent”

     android:layout_height=”fill_parent”

    >

 <TextView

    android:layout_width=”fill_parent”

    android:layout_height=”wrap_content”

    android:text=”@string/hello”

   />

</LinearLayout>

                                      

Registering Events for Views

Registering Events for Views :
                                                             "Views can fire events when users interact with them. For example, when a user touches a Buttonview, you need to service the event so that the appropriate action can be performed. To do so, youneed to explicitly register events for views.Using the same example discussed in the previous section, recall that the activity has two Buttonviews; therefore, you can register the button click events using an anonymous class as shown here:"


 exj:
 

package net.learn2develop.UIActivity;
import android.app.Activity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.widget.Toast;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainActivity extends Activity {
       public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
            Button btn1 = (Button)findViewById(R.id.btn1);
            btn1.setOnClickListener(btnListener);
            Button btn2 = (Button)findViewById(R.id.btn2);
            btn2.setOnClickListener(btnListener);
      }
      //   create an anonymous class to act as a button click listener
private OnClickListener btnListener = new OnClickListener()
{
   public void onClick(View v)


    {
      Toast.makeText(getBaseContext(),
      ((Button) v).getText() + “ was clicked”,
      Toast.LENGTH_LONG).show();
     }
};

override the keydown method

public boolean onKeyDown(int keyCode, KeyEvent event)
{
   switch (keyCode)
   {
      //...
     //...
   }
   return false;
  }
}





"If you now press either the OK button or the Cancel button, the appropriate message will be displayed 

proving that the event is wired up properly."