Android

RecyclerView is successor to ListView.It is more efficient in displaying large datasets without too much overhead.RecyclerView consists of two main components  to achieve this:

1. adapter
2. layout manager

To use RecyclerView you need to add the RecyclerView in the view of the activity

In the activity class retreivethe RecyclerView using the findViewById() method

Set the adapter using the setAdapter() method

recyclerView.setAdapter(adapter);

Set the Layout manager using the setLayoutManager() method

recyclerView.setLayoutManager(layoutManager);

RecyclerView has these builtin layout managers:

• LinearLayoutManager
• GridLayoutManager
• StaggeredGridLayoutManager

<RelativeLayout xmlns:android=”http://schemas.android.com/apk/res/android”
xmlns:tools=”http://schemas.android.com/tools”
android:layout_width=”match_parent”
android:layout_height=”match_parent”
tools:context=”com.androidcookbook.recyclerviewdemo.ListActivity”>

<android.support.v7.widget.RecyclerView
android:id=”@+id/recyclerView”
android:layout_width=”match_parent”
android:layout_height=”match_parent”/>
</RelativeLayout>

An important concept in Adapter of RecyclerView is ViewHolder.List items contains reference to ViewHolder objects.ViewHolder implementation should cache the expensive findViewById(int) methods.

 

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SQLite is a RDBMS(relational database management system).There are many other RDBMS available such as Oracle, MySQL and SQL Server.SQLite differs from these RDBMS since it is not a client server database management system.Unlike other RDBMS SQLite is a embedded RDBMS.

SQLite is embedded as a part of the the mobile application.This means that you don’t need to install or setup SQLite to use it.You manage RDBMS by directly executing commands.This allows it to be a very lightweight RDBMS and suitable for embedded applications.

Here we will understand how to perform read and update operations using SQLite.

We will use a Java class SQLiteOpenHelper for performing different operations on the SQLite database.We will create a subclass derived from this class.The sublcass will implement the methods onCreate(SQLiteDatabase)  and onUpgrade(SQLiteDatabase, int, int) 

onCreate method is called when database is created.

onUpgrade You call this method when the database scheme needs to be modified.

Create a sub class deriving from the SQLiteOpenHelper class

public class DatabaseHandler extends SQLiteOpenHelper {…

import the following packages

android.database.sqlite.SQLiteOpenHelper
android.database.sqlite.SQLiteDatabase

In the constructor call the super class constructor.Also pass the database name and version as arguments

public DatabaseHandler(Context context) { 
super(context, "SampleDatabase", null, 1); 
}

Override the onCreate method.Create the tables required in this method.

@Override 
public void onCreate(SQLiteDatabase db) { 
String EMP_TABLE ="CREATE TABLE Employees ("ID INTEGER PRIMARY KEY,NAME TEXT,DEPARTMENT TEXT)";db.execSQL(EMP_TABLE); 
}

Override the onUpgrade method if required

public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
// db.execSQL(ALTER TABLE COMMAND); 
// onCreate(db); 
}

 

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ListView is used to display multiple items at a time.The items are displayed in rows.This allows the user to view multiple items at a time.Also the user can select the items from the list view.

To use listview in a android application you first define the layout or view of the Activity.In this layout you declare the ListView.Data is provided to the ListView using the setListAdapter() method.There are several implementations of the ListAdapter.But the most basic is BaseAdapter in the android.widget package.Rows are created by the adapter

To use ListView in Android application first declare the <ListView> XML element in the layout.

<ListView android:id="@+id/ListView01"
android:layout_width="wrap_content"
android:layout_height="fill_parent"/>

In the Activity class retreive the ListView by calling the findViewById() method.

ListView listView = (ListView) findViewById(R.id.ListView01);

Create a ListAdater as:

BaseAdapter adapter=new BaseAdapter() {

public int getCount() {
return words.length;
}

public Object getItem(int position) {
return words[position];
}

public long getItemId(int position) {
return position;
}

public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater =
(LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
View view = inflater.inflate(R.layout.list_row, null);
TextView textView = (TextView) view.findViewById(R.id.TextView01);
textView.setText(words[position]);
return view;
}

Set the ListAdapter by calling the listView.setAdapter() method and passing the ListAdapter created in the above step

listView.setAdapter()

Define a layout for every row in the ListView in the res/layout directory:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content" android:layout_height="wrap_content">
<TextView android:text="@+id/TextView01" android:id="@+id/TextView01"
android:layout_width="fill_parent" android:layout_height="wrap_content"/>
</LinearLayout>

 

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Toast notification is a mechanism in Android application to display a message for short duration to the user.The Toast notification is displayed on top of the current screen and occupies partial screen space.It is like a popup in windows applications.It goes away itself after a short duration.

To display toast notification in Android you need to call the following two methods of the Toast object:

• makeText()
• show()

To display the toast notification first create and set properties of the toast object using the following code:

Toast.makeText(context, message, length).show();

• context : Represents an activity
• message: Message that is to be displayed to the user

After this show the toast notification using the show() method:

toast.show();

Custom Toast Notification

Define the view to be used with toast:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/custom_toast"
android:orientation="horizontal"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView android:id="@+id/text"
android:layout_width="wrap_content"
android:layout_height="fill_parent"
android:textColor="#000000"
/>
</LinearLayout>

Use the LayoutInflater,which connects the view with the viewgroup, using the following code:

LayoutInflater inflater = getLayoutInflater();
View layout = inflater.inflate(R.layout.custom_toast,
(ViewGroup) findViewById(R.id.container));

After this we are setting the text of the text layout by using the following code:

TextView text = (TextView) layout.findViewById(R.id.text);
text.setText("This is a custom toast");

Finally we are creating a toast object:

Toast toast = new Toast(getApplicationContext());
toast.setGravity(Gravity.CENTER_VERTICAL, 0, 0);
toast.setDuration(Toast.LENGTH_LONG);
toast.setView(layout);
toast.show();

 

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You can inform the user about the different actions he can take using the AlertDialog class.This class allows the user to take three different actions which are Positive action,Neutral action ,negative action.

These actions are set using the different methods of the AlertDialog class.The different actions which user can take using the AlertDialog are:

• User can take Positive action which means user wants to execute the corresponding action.Call the setPositiveButton() method in this scenario.
• User can take Neutral action which means that user wants to postpone the action..Call the setNeutralButton() method in this scenario.
• User can take the Negative action.Call the setNegativeButton() in this scenario.

The methods used to indicate the various actions taken by the user such as positive action or negative action are defined by the AlertDialog.Builder class.The Builder class is a nested class defined in the AlertDialog class.

For showing dialog you need to create an AlertDialog object.Once you create this object you need to call the different methods corresponding to the different positive,negative and neutral scenarios.

To create alert dialog

Create an object of type AlertDialog

Call the different methods of the AlertDialog object.To set the title call the setTitle() method.Similarly call the setMessage() method to set the message.

Provide the callbacks for:

• Positive action
• Neutral action
• Ngative action

alertDialogBuilder = new AlertDialog.Builder(this);
alertDialogBuilder.setTitle("title");
alertDialogBuilder.setMessage("message")
alertDialogBuilder setPositiveButton("positivemessage", new AlertDialog.OnClickListener() {
public void onClick(DialogInterface dialog, int action) {
//
}
});
alertDialogBuilder .setNeutralButton(R.string.discard_changes, new AlertDialog.OnClickListener() {
public void onClick(DialogInterface dialog, int action) {
//
}
})
alertDialogBuilder .setNegativeButton(android.R.string.cancel_dialog,
new AlertDialog.OnClickListener() {
public void onClick(DialogInterface dialog, int action) {
//
}
})
.create();
alertDialog.show();

 

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