Develop Reference

How to know which button user clicked and its text and id in Android Studio?

Through out the whole android application I want to capture button click, radio button clicks, link click etc... basically a user interaction in whole android application. Is there any common method to detect which element user click and its values.?

Try using onCickListener() on the buttons.

In Kotlin:
Add id to button in .xml files with android:id="#+id/nameOfButton". Every button needs an unique name.
In .kt file, use setOnClickListener with the id to set up the action when user click the button.
If there are several buttons, just follow step 1 and 2.
Example:
step 1
<Button
android:id="#+id/buttonSave"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Save" />
step 2
buttonSave.setOnclickListenter {
//TODO: your code goes here
}

Its very simple you just need to get the text and id of button from the onclick method. Here is java and xml code for it:
XML:
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/button"
android:onclick="getid"
android:text="Save" />
JAVA:
public void getid(View v){
int id = v.getId();
String text = v.getText();
}

As #Muthukumar Lenin asked here is listview in xml and java
XML:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/rl"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="10dp"
tools:context=".MainActivity">
<TextView
android:id="#+id/textview"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textStyle="italic"
android:textColor="#5f65ff"
android:padding="5dp"
android:text="Choose is the best football player?"/>
<ListView
android:id="#+id/listview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#id/textview" />
</RelativeLayout>
JAVA:
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ListView listView = (ListView) findViewById(R.id.listview);
final TextView textView = (TextView) findViewById(R.id.textview);
String[] players = new String[] {"CR7", "Messi", "Hazard", "Neymar"};
List<String> Players_list = new ArrayList<String>(Arrays.asList(players));
ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, Players_list);
listView.setAdapter(arrayAdapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String selectedItem = (String) parent.getItemAtPosition(position);
textView.setText("The best football player is : " + selectedItem);
}
});
}
}
Some of these code are from tutorialspoint and some are edited by me.

button onclick from a layout file

so I was working on some basics of android when I stumbled upon this. I am trying to implement a listview(having its layout stored in file eachrow.XML)and a button on my app such that when the user clicks one button "schoollife", the listview automatically imports layout stored from other file "eachrow2.XML".
the layout of eachrow.xml consists of buttons only, while the layout of eachrow2.xml consists of buttons.
Everything seems to work fine, the user clicking the button imports the other layout , but the problem starts when user tries to click buttons from the second layout. in the error logs, it is stating that the button 'subject' causing a null pointer exception
eachrow.xml:
eachrow2.xml:
===========codes========
eachrow2.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="horizontal">
<Button
android:id="#+id/subjectbutton"
android:layout_width="wrap_content"
android:layout_height="100dp"
android:padding="1dp"
android:layout_margin="1dp"
android:textAllCaps="false"
android:background="#color/colorPrimary"
android:textColor="#color/white"
/>
<TextView
android:id="#+id/marksbox"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:textSize="20dp"
android:text="click the button to show marks of each subject"
android:textAlignment="center"
/>
</LinearLayout>
mainactivity.java:
package com.example.ansh.reportcard;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import java.util.HashMap;
public class MainActivity extends AppCompatActivity implements View.OnClickListener{
private ListView l;
private String[] d_myself;
private ArrayAdapter adp;
private HashMap<String,String> d_school;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
l=(ListView)findViewById(R.id.a_list);
d_myself= new String[]{"something"
};
d_school=new HashMap<>();
d_school.put("A","B");
Button B_myself= (Button)findViewById(R.id.myself);
B_myself.setOnClickListener(this);
Button B_school=(Button)findViewById(R.id.school);
B_school.setOnClickListener(this);
Button subject=(Button)findViewById(R.id.subjectbutton);
subject.setOnClickListener(this);
}
#Override
public void onClick(View view) {
if(view.getId()==R.id.myself){
adp=new ArrayAdapter(MainActivity.this,R.layout.eachrow,R.id.textView,d_myself);
l.setAdapter(adp);
}
if (view.getId()==R.id.school){
adp=new ArrayAdapter(MainActivity.this,R.layout.eachrow2,R.id.subjectbutton,d_school.keySet().toArray());
l.setAdapter(adp);
}
if (view.getId()==R.id.subjectbutton){
Button tmp=(Button)view;
CharSequence x=tmp.getText();
TextView t= (TextView) findViewById(R.id.marksbox);
t.setText(d_school.get(x.toString()));
}
}
}

According to my understanding to your question, You declaring the Button from the xml file activity_main.xml, Instead you should find it from the eachrow2.xml file.
The subjectbutton is in the eachrow2.xml so you need to find the view from this file only instead activity_main.xml.

Displaying list in Android fragment

I got a fragment that should only display a list but every time I try to display the list the previous activity is displayed in the background.
So my question is, how do I display the list on a empty page? What can I put instead of getActivity() in the ArrayAdapter.
My XML looks like this:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<ListView
android:id="#+id/fundraiser"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
</ListView>
And my code looks like this
import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
public class FundraiserFragment extends ListFragment{
String[] values = new String[] { "Item 1", "Item 2", "Item 3"};
#Override
public void onActivityCreated(Bundle savedInstanceState){
super.onActivityCreated(savedInstanceState);
ArrayAdapter<String> adapter = new ArrayAdapter<String>
(getActivity(),android.R.layout.simple_list_item_1,values);
setListAdapter(adapter);
}

Don't forget that layouts are transparent by default, unless you assign them a background color.
Assign a background color to the LinearLayout of your fragment in the XML file and the parent activity should disappear.
android:background="#android:color/white"

How to get multiple selected items from a ListActivity in Android

I am basically trying to get which items have been selected within a multiple choice enabled ListActivity. I am sure that there are many beginning Android programmers that would love this to be clarified. This app runs fine until it gets to the FOR loop and tries to assign the values of the multi-choice items to ArrayList 'items'. I'm simply trying to use Toast to see if the multi-choice items are being assigned to the Arraylist 'items'. The app crashes when the button is clicked. testing is done in android 2.2 emulator
Here is my Main.xml layout
<?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" />
<Button android:id="#+id/button"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Selected Items" />
<ListView android:id="#android:id/list" android:layout_width="fill_parent"
android:layout_height="wrap_content" android:choiceMode="multipleChoice"
android:textFilterEnabled="true" android:fastScrollEnabled="true" >
</ListView>
</LinearLayout>
and here is the code
package com.tests.TestCode;
import android.app.ListActivity;
import android.os.Bundle;
import java.util.ArrayList;
import android.util.SparseBooleanArray;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;
public class MainActivity extends ListActivity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
final String[] list = {"wrenches","hammers","drills","screwdrivers","saws","chisels","fasteners"};
// Initializing An ArrayAdapter Object for the ListActivity
final ArrayAdapter<String> adapter = new ArrayAdapter<String> (this, android.R.layout.simple_list_item_multiple_choice, list);
setListAdapter(adapter);
Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
ListView thelistview = (ListView) findViewById(android.R.id.list);
ArrayList<String> items = null;
SparseBooleanArray checkedItems = thelistview.getCheckedItemPositions();
if (checkedItems != null) {
for (int i=0; i<checkedItems.size(); i++) {
if (checkedItems.valueAt(i)) {
String item = adapter.getItem(checkedItems.keyAt(i)).toString();
items.add(item);
}
}
Toast.makeText(getBaseContext(), items.toString(), Toast.LENGTH_LONG).show();
} else {
Toast.makeText(getBaseContext(), "checkedItems == null", Toast.LENGTH_LONG).show();
}
}
});
}
}
Much obliged to anyone that can provide a good answer as to the best way to go about accomplishing this ListActivity scenario, or anyone that can explain why the app crashes at the point of assignment to the ArrayList. Thanks!

Your items list is null and you try to use it before initializing it.
You need to use items = new ArrayList<String>(); somewhere before trying to use it, or you will keep getting NullPointerExceptions.

Android listView within tabwidget activity gives exception

Using Google's "Hello TabWidget" tutorial found here I was able to build a tabWidget layout, but I'm having a seriously difficult time trying to stick a listview within one of the tabs.
I've also read through a couple threads here about this issue, but they all pertain to assigning the ListView to the specific id "list", which I have done, but I still get a null pointer exception.
I have spent wayyyyyyy to much time on this elementary objective, so I've asked God for help, but I think he's busy right now. Anyone on a lunch break?
the activity in which the ListView is called
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;
public class SettingsActivity extends Activity {
private ListView lv;
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.settings);
String[] settingsList = getResources().getStringArray(R.array.settingsStringArray);
lv = (ListView) findViewById(R.id.list);
lv.setAdapter(new ArrayAdapter<String>(this, R.id.TextView01, settingsList));
lv.setOnItemClickListener
(new OnItemClickListener()
{
public void onItemClick(AdapterView<?> parent, View view,int position, long id)
{
Toast.makeText(getApplicationContext(), ((TextView) view).getText(),Toast.LENGTH_SHORT).show();
}
});
}
}
xml file from res/layout called within setContentView(R.layout.settings)
<?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">
<ListView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="#+id/list">
</ListView>
<TextView
android:id="#+id/TextView01"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
</TextView>
</LinearLayout>
Thanks, everyone.

Your TextView01 needs to go into a separate XML file, say textview01. (The name needs to be lowercase, although the only error message you'll see about this will be in the console.) You would then access it as R.layout.textview01.