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);
Related
hello I want put one button . when click that button from this page go to another page. I think I use Relative layout but I don't know exactly how to use it. please put complete code from "main.xml" and "activity" because I'm an amateur!!! thanks
Oh silverboy...
MainActivity:
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.button).setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, SecondActivity.class));
}
});
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Go to second page"/>
</RelativeLayout>
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.
In my application I want to add a button at a unique position doing the same function in all activities, so instead of adding the same code to all activities, I thought of making a base activity, and here it is.
mport android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageButton;
import android.widget.Toast;
public abstract class DefaultActivity extends Activity{
ImageButton b;
#Override
public void onCreate(Bundle bundle)
{
super.onCreate(bundle);
setContentView(R.layout.default_activity);
b = (ImageButton)findViewById(R.id.imageButton1);
b.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
Toast.makeText(getApplicationContext(), "ana fel base activity", Toast.LENGTH_LONG).show();
}
});
}
}
But the button doesnt appear in the other activities although I made other activities extend DefaultActivity. So is there a way to make this happen? Thanks alot.
P.S: I don't want to use the actionBar.
If your other activities call setContentView(...) with other layouts, then those layouts are going to be shown. If those layouts don't have your ImageButton, then you won't have an ImageButton on screen (layouts won't "nest" by calling setContentView() in both the Activity and it's superclass implementation). One solution is to use the <include> tag in your other layouts and have another layout file with just the ImageButton like so:
res/layout/image_button.xml
<ImageButton xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
...
/>
res/layout/activity_main
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<!-- more views ... -->
<include android:layout="#layout/image_button" />
</LinearLayout>
I just started some android programming recently and I am creating a small project app.
I have a few different XML Layout files and want my button to go to that layout. However, when I press the button on the emulator I get this message "Unfortunately "MyApp" Has stopped".
Here is my Main Activity Class:
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainActivity extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Shows the Activities screen.
Button Button1=(Button)findViewById(R.id.Button1);
Button1.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent i = new Intent(MainActivity.this,ActivityList.class);
startActivity(i);
}
});
}
This is my XML CODE for the Button:
android:id="#+id/Button1"
android:layout_width="300dp"
android:layout_height="55dp"
android:layout_alignLeft="#+id/Menutxt"
android:layout_below="#+id/Menutxt"
android:layout_marginTop="20dp"
android:gravity="center"
android:text="#string/Choose_Activity"
android:textColor="#ffffffff"
android:textSize="25sp"
android:typeface="serif"
I was wondering if anyone could help me out here, been trying to do this for a few hours and cannot get past it. Thanks.
add this to the layout of the activity that you wish to open. it should go at the top: tools:context=".activity" >
e.g.
<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:orientation="horizontal"
tools:context=".activity" >
replace "activity" with the name of your activity
You did not show us your ActivityList.class , maybe you have created and extends Activity, but make sure that in your AndroidManifest.xml has this code:
activity android:name=".ActivityList"
I have a problem with my Android app. I have three Activities that all connect with one another with a Image button.
My problem is I can't go back on any of the pages, just forwards. I have been reading about the back button and how to keep its state and not kill (End) it, so the user can click back if needed too.
I am new to Android and I know there's a lot to learn. So thank you for your help.
Java code for first Activity:
package my.hope;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageView;
import android.content.Intent;
public class NewhopeActivity extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ImageView myImage = (ImageView) findViewById(R.id.imagebutton1);
myImage.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
Intent intent = new Intent(NewhopeActivity.this, Act2.class);
startActivity(intent);
}
});
}
}
XML code:
<?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" android:background="#drawable/mint">
<ImageButton
android:id="#+id/imagebutton1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="250dp"
android:background="#drawable/ic_launcher"
android:onClick="Act2"
android:src="#drawable/ic_launcher" />
</LinearLayout>
What happens when you click the back button on your device? Unless specified, it kills the current activity and brings you back to the previous one.
However, if you wish to specify exactly what would clicking the back button do, you can override the onBackPressed() method:
#Override
public void onBackPressed() {
Intent intent = new Intent(CurrentActivity.this, NextActivity.class);
startActivity(intent);
finish();
}