android development

Introduction The Android system provides us with some standard widgets like TextView , Button ,EditText , ImageView etc which are commonly used in most of the Activities. Thus knowing their details is essential to proceed further.

TextView Purpose: To display text to the user Class: android.widget.TextView Important Properties: • android:typeface To display text in typeface like normal,sans,serif,monospace Eg: In XML android:typeface=“serif” In java t.setTypeface(Typeface.SERIF);

*Android development* • android:textStyle To display text in normal,bold and italic

Eg: In XML android:textStyle=“italic” In java t.setTypeface(null,Typeface.ITALIC); • android:textColor To set color of the text in hex format

Eg: In XML android:textColor=“#FF0000” In Java tv.setTextColor(Color.GREEN);

ImageView Purpose: To display Image to the user Class: android.widget.ImageView Steps Reqd To display Image 1. Store the image in res/drawable-ldpi, res/drawable-mdpi or res/drawable-hdpi folders

*Android development* 2. Add the ImageView widget to XML file 3. Set the “src” attribute of ImageView to the image to

be displayed. It’s syntax is: android:src=“@drawable/<img nam>” For eg: android:src=“@drawable/smiley” 4. To programmatically set the image we call the setImageResource() method of ImageView whose protoype is: public void setImageResource (int resId)

Example 6 Write a program to display an

image and change it on button click

main.xml <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android " android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" />

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<ImageView android:id="@+id/myimg" android:layout_width="wrap_content" android:layout_height="wrap_content" android:src="@drawable/scenery" /> <Button android:id="@+id/btn1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Click To Change" /> </LinearLayout>

ImageDemoActivity.java package kapoor.sachin.androidapps; import import import import import import

android.app.Activity; android.os.Bundle; android.view.View; android.view.View.OnClickListener; android.widget.Button; android.widget.ImageView;

public class ImageDemoActivity extends Activity implements OnClickListener { private Button b1; private ImageView imgv1;

@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); b1=(Button)findViewById(R.id.btn1); imgv1=(ImageView)findViewById(R.id.myimg); b1.setOnClickListener(this); } public void onClick(View v) { imgv1.setImageResource(R.drawable.android); } }

EditText Purpose: To display editable text to the user Class: android.widget.EditText Important Properties: Along with standard TextView properties following properties are supported • android:autoText To control spelling assistance Eg: android:autoText=“true”

• android:capitalize To automatically capitalize

whatever user types. Possible values are none,sentences,words,characters Eg: android:capitalize=“characters” • android:digits To configure text field to only accept

specific digits Eg: android:digits=“12345”

• android:singleLine To allow or disallow multiple

lines Eg: android:singleLine=“false” • Android:inputType To restrict the type of input .

Some possible values are text,textPassword,number,phone, date,textMultiLine,time,datetime Eg: android:inputType=“number”

Two useful methods of EditText are public Editable getText() (for obtaining contents of EditText) public void setText(CharSequence) (for setting contents of EditText)

The Toast Class Purpose: To display quick little message to the user Class: android.widget.Toast Important Constants: public static final int LENGTH_LONG : Show the view or text notification for a long period of time. public static final int LENGTH_SHORT :Show the view or text notification for a short period of time.

 Important Methods:

public static Toast makeText (Context , CharSequence , int ) To make a standard toast that just contains a text view with the text from a resource. public static Toast makeText (Context , int , int ) To make a standard toast that just contains a text view with the text from a resource id

 public void show ()

To display the message  public void setText (CharSequence) To update the text in a Toast that was previously created using one of the makeText() methods.  public void setDuration (int duration) To set how long to show the message for.

 Example:

Toast.makeText(this, “Welcome To Android", Toast.LENGTH_SHORT).show()

CheckBox Purpose: To display a specific type of two-states button that can be either checked or unchecked. Class: android.widget.CheckBox Important Methods: public boolean isChecked() To determine the state of CheckBox

 public void setChecked(boolean )

To change the checked state of this button.

RadioButton Purpose : To display a two-states button that can be either checked or unchecked. When the radio button is unchecked, the user can press or click it to check it. However, contrary to a CheckBox, a radio button cannot be unchecked by the user once checked.

 Class : android.widget.RadioButton

Creating Mutually Exclusive RadioButtons RadioButtons need to be grouped together in order to be mutually exclusive and for this we use RadioGroup objects. When several radio buttons live inside a radio group, checking one radio button unchecks all the others.

Example 7  Write an application to contain three radio buttons

representing 3 std colors and clicking on them should change the background color accordingly.

main.xml <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" android:id="@+id/l1" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" /> <TextView android:id="@+id/textView1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Choose A Color" android:textSize="30px"/>

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<RadioGroup android:id="@+id/radioGroup1" android:layout_width="wrap_content" android:layout_height="wrap_content" > <RadioButton android:id="@+id/rdred" android:layout_width="wrap_content" android:layout_height="wrap_content" android:checked="true" android:text="Red Color" />

<RadioButton android:id="@+id/rdblue" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Blue Color" /> <RadioButton android:id="@+id/rdgreen" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Green Color" /> </RadioGroup>

RadioDemoActivity.java package kapoor.sachin.androidapps; import android.app.Activity; import android.graphics.Color; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.LinearLayout; import android.widget.RadioButton; import android.widget.RadioGroup; public class RadioDemoActivity extends Activity implements OnClickListener{ private RadioButton r1,r2,r3; private LinearLayout lyt;

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public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); r1=(RadioButton)findViewById(R.id.rdred); r2=(RadioButton)findViewById(R.id.rdblue); r3=(RadioButton)findViewById(R.id.rdgreen); r1.setOnClickListener(this); r2.setOnClickListener(this); r3.setOnClickListener(this); lyt=(LinearLayout)findViewById(R.id.l1);

}

*Android development* public void onClick(View v) { switch(v.getId()) { case R.id.rdred: lyt.setBackgroundColor(Color.RED); break; case R.id.rdgreen: lyt.setBackgroundColor(Color.GREEN); break; case R.id.rdblue: lyt.setBackgroundColor(Color.BLUE); break; } } }