List and ArrayList Declaration

What is the difference between these two declarations:

Declaration 1 : ArrayList<String> arrayList = new ArrayList<String>();Declaration 2 : List<String> arrayList = new ArrayList<String>();

Answer: 
List is an interface. ArrayList, LinkedList.. etc are classes which implement list. When you are using List Interface,you have to iterate elements using List-Iterator and can move forward and backward,in the List where as in ArrayList Iterate using Iterator and its elements can be accessed unidirectional way.

Let's see in Brief Explanation:

List<String> arrayList = new ArrayList<String>();

Is generic where you want to hide implementation details while returning it to client, at later point of time you may change implementation from ArrayList to LinkedList transparently.

This mechanism is useful in cases where you design libraries etc., which may change their implementation details at some point of time with minimal changes on client side.

ArrayList<String> arrayList = new ArrayList<String>();

This mandates you always need to return ArrayList. At some point of time if you would like to change implementation details to LinkedList, there should be changes on client side also to useLinkedList instead of ArrayList.

What does android:layout_weight mean?

""android:layout_weight"" Meaning 

Specifies how much of the extra space in the layout to be allocated to the View.

LinearLayout supports assigning a weight to individual children. This attribute assigns an "importance" value to a view, and allows it to expand to fill any remaining space in the parent view. Default weight is zero

calculation to assign any remaining space between child

space assign to child = (child individual weight) / (sum of weight of every child in Linear Layout)

Example (1): if there are three text boxes and two of them declare a weight of 1, while the third one is given no weight (0), then remaining space assign to

1st text box = 1/(1+1+0) 2nd text box = 1/(1+1+0) 3rd text box = 0/(1+1+0)

Example (2) : let's say we have a text label and two text edit elements in a horizontal row. The label has no layout_weight specified, so it takes up the minimum space required to render. If the layout_weight of each of the two text edit elements is set to 1, the remaining width in the parent layout will be split equally between them (because we claim they are equally important).

calculation : 1st label = 0/(0+1+1) 2nd text box = 1/(0+1+1) 3rd text box = 1/(0+1+1)

If the first one text box has a layout_weight of 1 and the second text box has a layout_weight of 2, then one third of the remaining space will be given to the first, and two thirds to the second (because we claim the second one is more important).

calculation : 1st label = 0/(0+1+2) 2nd text box = 1/(0+1+2) 3rd text box = 2/(0+1+2)

Dynamically Table Row Creation Android

Dynamically Table Row Creation

In This Tutorial , it will show you how you can create the rows dynamically. Atfer Every click on the button, it will add rows dynamically.

MainActivity.java

public class MainActivity extends Activity implements OnClickListener{

Button btn;

int click=0;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

btn = (Button)findViewById(R.id.button1);

btn.setOnClickListener(this);

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

// Inflate the menu; this adds items to the action bar if it is present.

getMenuInflater().inflate(R.menu.activity_main, menu);

return true;

}

@Override

public void onClick(View v) {

TableLayout tl = (TableLayout)findViewById(R.id.mytable);

   TableRow tr = new TableRow(this);

   TextView tv= new TextView(this);

   click++;

   tv.setText("Created New Row: "+"Text:"+click);

   tr.addView(tv);

   tl.addView(tr,new TableLayout.LayoutParams(LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT));

}

}

activity_main.xml

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

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

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical"

    android:background="#eeeeee" >

    

<Button 

    android:id="@+id/button1" 

    android:layout_width="wrap_content" 

    android:layout_height="wrap_content" 

    android:text="Click To Add New Row Dynamically">

    

</Button>

<ScrollView 

    android:id="@+id/ScrollView01" 

    android:layout_width="wrap_content" 

    android:layout_height="wrap_content">

    <TableLayout 

        android:id="@+id/mytable" 

        android:layout_width="fill_parent" 

        android:layout_height="wrap_content" 

        android:stretchColumns="0">

  </TableLayout>

</ScrollView>

</LinearLayout>

Result: