Develop Reference

Trouble in changing button color on every click

I'm new to Android app.. I was trying to change the button color on first click and to change back to default on the next click and this will work no matter how many times user clicks...
Can anyone help me to understand this

Create global variable clickStatus
boolean clickStatus=true;
final Button running_app=(Button)findViewById(R.id.running_app);
running_app.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (clickStatus){
clickStatus=false;
running_app.setBackgroundColor(Color.parseColor("#3F51B5"));
}else {
clickStatus=true;
running_app.setBackgroundResource(android.R.drawable.btn_default);
}
}
});

Simple, Just give two different tags to button and keep toggling it on button click. That would help you to change background colour alternatively. Here is the complete code for it. Hope this helps.
Here is 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">
<Button
android:id="#+id/btnClick"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="Click Me" />
</LinearLayout>
Here is MainActivity.java
import android.graphics.Color;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private Button btnClick;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
btnClick = (Button) findViewById(R.id.btnClick);
btnClick.setOnClickListener(this);
btnClick.setTag("1");
btnClick.setBackgroundColor(Color.BLUE);
}
#Override
public void onClick(View view) {
if (view.getTag().equals("1")) {
view.setTag("0");
btnClick.setBackgroundColor(Color.RED);
} else {
view.setTag("1");
btnClick.setBackgroundColor(Color.BLUE);
}
}
}

How to make two diffrent Activities to use the same layout Android

Below code works fine, but it opens a new layout and shows the toast message. but i wanted it to show toast & popup menus on the current layout. I'm working on popup menu project, i want to show popup menu on same layout. Thanks in Advance.
MainMactivity.java
package com.example.twoact;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends Activity {
Button b1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
b1 = (Button) findViewById(R.id.button1);
b1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent openpopactivity = new Intent(MainActivity.this,
MainActivity2.class);
startActivity(openpopactivity);
}
});
}
}
MainActivity2.java
package com.example.twoact;
import android.widget.Toast;
import android.os.Bundle;
import android.os.Handler;
public class MainActivity2 extends MainActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
new Handler().postDelayed(new Runnable() {
public void run() {
Toast.makeText(getApplicationContext(), "ya am in",
Toast.LENGTH_SHORT).show();
}
}, 1000);
}
}
activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.twoact.MainActivity"
tools:ignore="MergeRootFrame" >
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="142dp"
android:text="Button" />
</RelativeLayout>

You can use Popup menu and Popup window. in this you can use your custom layout so you can get your view as window in same activity.
Popup window will be good option because it is since API LEVEL 1
please refer this docs and example 1,example 2
And Popup Menu is since API LEVEL 11. so you have to manage for lower version
docs for Popup Menu and example
popup window

Android Google Map API V2 - Buttons above fragment

I have managed to get a map to show on the screen. I am trying to create buttons above the map and then add actions to this. E.g. the button will change the location of the map. I am basically trying to adapt my code to this: https://www.youtube.com/watch?v=awX5T-EwLPc. However, I am using "extends Fragment Activity" which messes everything up.
My problem: I cannot create a button above the map, it is placed inside the map. I am trying to create a button above the map, and assign code so I can move to a location on the map etc. Here is my code:
MainActivity.java
package com.example.theapp;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends FragmentActivity implements OnClickListener
{
Button button;
TextView text;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button=(Button)findViewById(R.id.button1);
text=(TextView)findViewById(R.id.textView1);
}
#Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
text.setText("The button worked!");
}
}
activity_main.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:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<fragment
android:id="#+id/map"
android:layout_width="match_parent"
android:layout_height="match_parent"
class="com.google.android.gms.maps.SupportMapFragment" />
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/map"
android:layout_alignTop="#+id/map"
android:text="Button" />
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/button1"
android:layout_alignBottom="#+id/button1"
android:layout_alignRight="#+id/map"
android:layout_marginRight="39dp"
android:text="TextView" />
</RelativeLayout>
From the code, my app displays a button on the map and a text view. When you click the button, its meant to change the text, but it doesn't do anything. I have researched tutorials and by the looks of it, I will have to create multiple fragments?
Question: How would I be able to create a button on that page, that will then pin point the user on the map?
Thank you in advance.

You are not setting any functionality to the Button... You should use
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
text.setText("that's how you do it!");
}
});

You need not to worry about "FragmentActivity" until and unless you use fragment class.
Just use this as normal Activity. it will work well.
package com.example.theapp;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends FragmentActivity implements OnClickListener
{
Button button;
TextView text;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button=(Button)findViewById(R.id.button1);
button.setOnClickListener(this);
text=(TextView)findViewById(R.id.textView1);
}
#Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
text.setText("The button worked!");
}
}

when i change my button to an icon i can't click on it to go to a new layout

this my xml file main
<?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:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#raw/christmas"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/by_kostas"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="83dp"
android:text="#string/by_kostas"
android:textSize="20sp"
android:textColor="#F2F3F4"/>
<ImageView
android:id="#+id/settings"
android:layout_width="50dp"
android:layout_height="50dp"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:onClick="nameOfMethod"
android:src="#raw/settings" />
</RelativeLayout>
and my java Main
package com.kostas.mytorch;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.ImageView;
public class Main extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
//start our layout
super.onCreate(savedInstanceState);
setContentView(R.layout.main);{
final ImageView diskView = (ImageView) findViewById(R.id.settings);
diskView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v){
//my codes
}
});
diskView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v){
// System.out.println("image clicked...");//in my logcat
startActivity(new Intent("com.kostas.standroid.settings"));
}
});
}
}
my problem is when i click in the settings icon, my program crashes instead of what i wanted to create a new layout (settings xml is just black page),can someone be kind enough to help me out

You can attach click listener to any view by two ways:
In xml, write onClick attribute of the view and pass the method
name you have implemented in the activity.
Example: android:onClick="someMethod" and in the activity code, declare a method
public void someMethod(View view)
{
// handle click here
}
In activity, use setOnClickListener() to the view.
For now, try this:
diskView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v){
// System.out.println("image clicked...");//in my logcat
startActivity(new Intent(Main.this, settings.class));
}
});
Also remove this line from xml: android:onClick="nameOfMethod"

Some time there is contextual problem. Try this.
Intent intent = new Intent(CurrentActivity.this, UpcomingActivity.class);
startActivity(intent);
Also don't forget to define class in Manifest file

try to remove
android:onClick="nameOfMethod"
from the xml layout. I believe this is the method that it's called when you click the settings button and it doesn't exist so it crashes.

Android Null Pointer Exception Button

Ok this may seem like a pointless example but if I can figure this out then the program I am trying to make will work. So I have two activities test and test two each with one button.
Test 1:
package thompson.cameron.com;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
public class Test extends Activity implements OnClickListener {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
View button = findViewById(R.id.testButton);
button.setOnClickListener(this);
}
public void onClick(View v){
Intent i = new Intent(this, Test2.class);
startActivity(i);
}
}
and test2
package thompson.cameron.com;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
public class Test2 extends Activity implements OnClickListener {
#Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main2);
View test = findViewById(R.id.testButton);
test.setOnClickListener(this);
}
public void onClick(View v){
switch (v.getId()){
case R.id.testButton:
System.exit(1);
}
}
}
When I click the button on Test it is supposed to launch test2 however it is at this point I get an null pointer exception that I have narrowed down to test.setOnClickListener(this); line of code. Below are my two xml files for the layout. I can get the button to work when I only have one activity but as soon as I add a second activity with a different layout file it all falls apart
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button
android:id="#+id/testButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TEST TEST TEST"/>
</LinearLayout>
main2.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button
android:id="#+id/testButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TEST2 TEST2 TEST2"/>
</LinearLayout>
I'm still new at Android programming so thanks for all your help.

Open the Debug perspective in Eclipse
Choose the 'Breakpoints' view tab.
Select the 'Add Java Exception Breakpoint' and choose
NullPointerException.
Launch your activity, either by using 'Debug As...' or attaching
the debugger to a running instance via DDMS.
Execute the offending workflow. It will break on the line that
caused the NullPointerException.

In your test.java file give:
implements View.OnClickListener
Initialize your button as:
Button testButton = (Button) findViewById(R.id.testButton);
and inside your onClick method, check whether you are clicking button:
if(v == testButton) {
//give ur intent code
}
There are different ways to perform onClick functionality.
One is the above method which I have mentioned.
Another one is what ankit has mentioned.
Third way is through your layout.
Inside your layout for your button tag, you may give as:
<Button android:id="#+id/testButton" android:layout_height="wrap_content" android:layout_width="wrap_content" android:text="Click" android:onClick="onTestButtonClick" />
And inside your class just mention the below details for button:
public void onTestButtonClick(View view) {
//give your intent code
}
You may refer to the link also:
http://android-developers.blogspot.com/2009/10/ui-framework-changes-in-android-16.html

Make sure that both activities are register at the application's manifest file.
As a side note never call System.exit in your code. You can call finish() to close an Activity and this will bring at the front the previous Activity on the stack.

The issue here is that you haven't typecasted your views to buttons.
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button; // Needed to add this import for the button casting below
public class Test extends Activity implements OnClickListener {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// I have changed View to Button and then typecasted
// with the "(Button)" the return of findViewById
Button button = (Button) findViewById(R.id.testButton);
button.setOnClickListener(this);
}
public void onClick(View v){
Intent i = new Intent(this, Test2.class);
startActivity(i);
}
}
Let me know if you have any issues with this. I just completed my first experiment through using the onClickListener implementation through the main class instead of individual anonymous listeners.
Andrew

I had the same problem, you may put the same content view that the button,
setContentView(R.layout.main); if the button is in that content view, in other case, you will put:
setContentView(R.layout.buttoncontentview);
View button = findViewById(R.id.testButton);
button.setOnClickListener(this);
public void onClick(View v){
Intent i = new Intent(this, Test2.class);
startActivity(i);
}
setContentView(R.layout.main);
sorry for my bad english, but i'm spanish

Implement OnClickListener interface
and set button.setOnClickListener(this);
and override
public void onClick(View v) {
}

I think your buttons IDs need to be different in different activities. R.id.testButton would refer to only one button.

The final solution is that you may modify the AndroidManifest.xml file, i finally solved my error in this link How to register a new activity in AndroidManifest.xml?

You can try this.it may work.
package thompson.cameron.com;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
public class Test extends Activity{
private Button button;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
button = findViewById(R.id.testButton);
button.setOnClickListener(new OnClickListener() {
public void onClick(View arg0) {
Intent i=new Intent().setClass(Test.this,Test2.class);
startActivity(i);
}
});
}
}

First of all in main.xml and main2.xml chage the button's ids like in below code.
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button
android:id="#+id/testButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TEST TEST TEST"/>
</LinearLayout>
main2.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button
android:id="#+id/testButton1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TEST2 TEST2 TEST2"/>
</LinearLayout>
It throws nullpointerexception because of id confict with each other so in your java file use following code to find button.
In Activity 1
Button button = findViewById(R.id.testButton);
button.setOnClickListener(this);
and
In Activity 2
Button button = findViewById(R.id.testButton1);
button.setOnClickListener(this);