Kotlin :: Android Button Click Listener - Global Declaration

We will get Button action in 3 steps (Button declared as a Globally)

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1. Create Globar variable for Button

lateinit var button : Button;

2. get Button reference from xml

button=findViewById(R.id.button) as Button;

3. set OnClickListener to Button

button.setOnClickListener(View.OnClickListener {
                   });

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Screen Shots:

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1. MainActivity.kt

class MainActivity : AppCompatActivity() {
    lateinit var button : Button;

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        button=findViewById(R.id.button) as Button;

        button.setOnClickListener(View.OnClickListener {
           Toast.makeText(applicationContext,"You Clicked  

                       Button",Toast.LENGTH_SHORT).show();
        });

    }

}

2.  activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:background="#FF00FF"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/button"
        android:textStyle="bold"
        android:textSize="20dp"
        android:text="Click Me"
        android:textColor="#ffffff"
        android:layout_width="200dp"
        android:layout_height="50dp"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true" />

</RelativeLayout>

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Android JSONObject String Parsing Explanations

While parsing JSONObject String we will use below methods

1. has("key_name");

it used for check specific KEY is exists or not

if key exists in jsonObject it returns TRUE otherwise it returns FALSE.

                            

2. isNull("key_name");

it used for check specific OBJECT exists or not, if exists it

checks specific object is NULL or not

if key not exists or exists but equals NULL it returns TRUE otherwise it returns FALSE.

                            

3. keys();

Used for get all keys exists from JSON

                            

4. getBoolean("key_name");

Used for get boolean value from JSON;

                            

5. getInt("key_name");

Used for get Integer value from JSON;

                            

6. getLong("key_name");

Used for get Long value from JSON;

                            

7. getDouble("key_name");

Used for get Double value from JSON;

                            

8. getString("key_name");

Used for get String value from JSON;

                            

9.get("key_name");

Used for get Object value from JSON;

                            

10. getJSONObject("key_name");

Used for get JSONObject value from JSON;

                            

11. getJSONObject("key_name");

Used for get JSONArray value from JSON;

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Sample JSON String:

{"boolean_key":true,"int_key":42798,"long_key":5349,"double_key":70.25,"string_key":"ganesh","json_object_key":{"name":"venkat","phno":"0123456789","city":"Hyd"},"json_array_key":[50,60,70,80]}

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1. has("key_name");

Syntax:

jsonObject.has("key_name");

it used for check specific KEY is exists or not

if sno key exists in jsonObject it returns TRUE otherwise it returns FALSE.

Example

boolean b1 = jsonObject.has("string_key");

boolean b2 = jsonObject.has("int_key");

boolean b3 = jsonObject.has("dummy_key");

                            

show output in Log

Log.e("value1", b1 + "");

Log.e("value2", b2 + "");

Log.e("value3", b3 + "");

                            

Output

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true

true

false

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2. isNull("key_name");

Syntax

jsonObject.isNull("object_key_name");

it used for check specific OBJECT exists or not, if exists it checks specific object is NULL or not

if key not exists or exists but equals NULL it returns TRUE otherwise it returns FALSE.

Example

boolean b1 = jsonObject.isNull("dummy_object_key");

boolean b2 = jsonObject.isNull("json_object_key");

boolean b3 = jsonObject.isNull("json_array_key");

show output in Log

Log.e("value1", b1 + "");

Log.e("value2", b2 + "");

Log.e("value3", b3 + "");

Output

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true

false

false

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3. keys();

Syntax

jsonObject.keys();

Used for get JSONArray value from JSON;

Ex

Iterator<String> jsonKeys = jsonObject.keys();

show output in Log

int i = 0;

while (jsonKeys.hasNext()) {

Log.e("Value", "Keys : " + i + " : " + jsonKeys.next());

                                      i++;

}

Output

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Keys : 0 : boolean_key

Keys : 1 : int_key

Keys : 2 : long_key

Keys : 3 : double_key

Keys : 4 : string_key

Keys : 5 : json_object_key

Keys : 6 : json_array_key

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4. getBoolean("key_name");

         

Syntax

jsonObject.getBoolean("boolean_key_name");

Used for get boolean value from JSON.

Ex

boolean b = jsonObject.getBoolean("boolean_key");

show output in Log

Log.e("Value", "boolean : " + b);

Output

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boolean : true

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5. getInt("key_name");

Syntax

jsonObject.getInt("int_key_name");

Used for get Integer value from JSON;

Ex

int i = jsonObject.getInt("int_key");

show output in Log

Log.e("Value", "int : " + i);

Output

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int : 42798

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6. getLong("key_name");

Syntax

jsonObject.getLong("long_key_name");

Used for get Long value from JSON;

Ex

long l = jsonObject.getInt("long_key");

show output in Log

Log.e("Value", "long : " + l);

Output

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long : 5349

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7. getDouble("key_name");

Syntax

jsonObject.getDouble("double_key_name");

Used for get Double value from JSON;

Ex

double d = jsonObject.getInt("double_key");

show output in Log

Log.e("Value", "double : " + d);

Output

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double : 70.0

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8. getString("key_name");

Syntax

jsonObject.getString("string_key_name");

Used for get String value from JSON;

Ex

String s = jsonObject.getString("string_key");

show output in Log

Log.e("Value", "String : " + s);

Output

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String : ganesh

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9.get("key_name");

Syntax

jsonObject.get("object_key_name");

Used for get Object value from JSON;

Ex

Object o1 = jsonObject.get("json_object_key");

Object o2 = jsonObject.get("json_array_key");

show output in Log

Log.e("Value", "Object : " + o1);

Log.e("Value", "Object : " + o2);

Output

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Object1 : {"name":"venkat","phno":"0123456789","city":"Hyd"}

Object2 : [50,60,70,80]

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10. getJSONObject("key_name");

Syntax

jsonObject.getJSONObject("json_object_key_name");

Used for get JSONObject value from JSON;

Ex

JSONObject jsonObject1 = jsonObject

                                                .getJSONObject("json_object_key");

show output in Log

Log.e("Value", "JSONObject : " + jsonObject1);

Output

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JSONObject : {"name":"venkat","phno":"0123456789","city":"Hyd"}

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11. getJSONObject("key_name");

Syntax

jsonObject.getJSONObject("json_array_key_name");

Used for get JSONArray value from JSON;

Ex

JSONArray jsonArray = jsonObject.getJSONArray("json_array_key");

show output in Log

Log.e("Value", "JSONArray : " + jsonArray);

Output

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JSONArray : [50,60,70,80]

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    Download Full Source Code HERE

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