Develop Reference

button press in Android app creates casting error

I am new to android development, and have been trying to use the beginner's tutorial as my starting point for developing a simple app. There is one screen, with an image, a row of four buttons, a textbox for the user to enter a pin, and a textview to display results.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/linear_layout_1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ImageView
android:id="#+id/imageView1"
android:contentDescription="#string/image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="#drawable/skytrek"
/>
<LinearLayout
android:id="#+id/linear_layout_2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="14sp"
android:text="#string/button_today"
android:onClick="today_click" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="14sp"
android:text="#string/button_tomorrow"
android:onClick="tomorrow_click" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="14sp"
android:text="#string/button_this_week"
android:onClick="this_week_click" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="14sp"
android:text="#string/button_next_week"
android:onClick="next_week_click" />
</LinearLayout>
<EditText android:id="#+id/editText1"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:hint="#string/edit_message" />
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/init_message"/>
</LinearLayout>
I have code to deliver the results I want based on the button pressed - all fine. But then I wanted the user to enter a PIN as well as pressing a button, so I added the EditText control. This threw the following error:
E/AndroidRuntime(28578): Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.EditText
My Java class:
private String content = null;
private TextView textView1;
private EditText editText1;
public void today_click(View view) {
getPage("today");
}
public void tomorrow_click(View view) {
getPage("tomorrow");
}
public void this_week_click(View view) {
getPage("thisweek");
}
public void next_week_click(View view) {
getPage("nextweek");
}
public void getPage(String strParam) {
editText1 = (EditText) findViewById(R.id.editText1);
String message = editText1.getText().toString();
if (message.equals("4567")) {
content = "PIN recognised";
} else {
content = "PIN not recognised";
}
textView1 = (TextView) findViewById(R.id.textView1);
textView1.setText(content);
}
I thought I had done something silly, using the name of a TextView instead of an EditText control, but I can't find it if I have.
The error is being thrown at the line
getPage("thisweek");
I didn't understand how this line involved views of any sort, but of course the function heading
this_week_click(View view)
does, and when I changed the order of the TextView and the EditText in the XML file (so that the TextView comes first), the error disappeared. It is as if the "view" being passed is not the button, but the nearest widget to the button. I have read
existence of parameter (View view)
but it only seems to confirm my (mis)understanding that a button should be passed as the view parameter. I have also tried cleaning the project, and building a completely new project. What on earth is causing the casting error?

If you're using Eclipse, go to the menu voice "Project" and select "Clean"
Sometimes Eclipse has some problem with ids, by cleaning the project you regenerate them..

Everytime if you make any changes in xml or any interchange of position of views in xml or change of id's,you need to clean build your project.If not you will get this exception.

Hello I have tested your code, your code is fine. Please clean your project from
select your project then click on Project and then Clean and also check the Build Automatically . Your auto generated class R is not generated properly.

Try cleaning your project and run it again..
Eclipse -> Project menu ->Clean
It is because eclipse gets confused when we play around in the xml file ;)

fiewViewById not finding my button (Eclipse)

I downloaded latest ADT from the main website and it came with Eclipse. So, I set everything up fine > Start new Android project. Set my settings, and the Activity to "Blank Activity", click finish.
Now, I go to the visual editor and add a button and some text. The problem is, is that "findViewById" is not detecting the button for some reason. Yes, I "Cleaned" the project and all that..
Here's the xml portion:
<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"
tools:context=".MainActivity" >
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:layout_below="#+id/button1"
android:layout_marginTop="37dp"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:ems="10" >
<requestFocus />
</EditText>
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:layout_below="#+id/editText1"
android:layout_marginTop="52dp"
android:text="#string/button" />
</RelativeLayout>
Here's my source code:
package com.example.tcp;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.Button;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button ibtn = (Button) findViewById(R.id.button1); // Error
}
#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;
}
}

Did you actually save the activity_main.xml? View ID's are not accessible to the rest of the project until you save the layout you're working on.
I copied and pasted your code straight into a blank project and it worked fine after saving.

Its just the basic error so clean your project and build again if its not work then restart eclipse and start once again it will display your button.In the same way you followed
don't even import R.java it will show you error..
so clean and build your project

In your TextView you have
android:layout_below="#+id/button1"
Delete the plus so you have
android:layout_below="#id/button1"
Also it's better when you move the code of the textview below the code of the button. The Relative layout will position it where it's supposed to be anyway. But this way you don't link to an id that doesn't exist yet.
You declare a id with the + in the id. So in your case you declare it twice.
(Also for furure reference when you post something on StackOverflow with an error. Please mention the error in all cases. It makes finding the error and helping you a lot easier.)

I looked at the R file and it was empty before I "ran" the project. After clicking "run" it added the id fields in the file. Seems to be working fine now. I guess it was actually a problem with the activity_main.xml not saving. Thanks again

Unable to get the reference to spinner in the onCreate statement

public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_homepage);
Spinner spinner=(Spinner)findViewById(R.id.spinner1);
XML
<RelativeLayout xmlns:android="schemas.android.com/apk/res/android";
xmlns:tools="schemas.android.com/tools";
android:layout_width="match_parent"
android:layout_height="match_parent" >
<Spinner android:id="#+id/spinner1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
</RelativeLayout>

Suppose you have proper XML layout. Try to clean your project (aka recreate gen).
Project-> Clean -> Ok. After, refresh your project to recreate R.java. Might help you.
The other reason might wrong path for R.java file
Sometimes you don't see any import of R at all.
So add it manually: import [yourpackage].R
For example: import com.demo.agnt.R
or replace old one: for example import android.R to import [yourpackage].R

Beginner Android why is "id" is "Unknown member" with R.id?

I'm sure this is something dead simple as it's my first android app with code (the hello world example I did was just assigning a value to a string in XML). My problem is when trying to get the reference for my button in my variable then the id as in R.id is not defined?
The compiler error is in a comment in the code below where it occurs:
package com.geeksonhugs.simplecalc;
import android.app.*;
import android.os.*;
import android.view.*;
import android.widget.*;
public class MainActivity extends Activity
{
private Button AddButton;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
AddButton = (Button)findViewById(R.id.btnAdd);
//"Unknown member 'id' of 'com.geeksonhugs.simplecalc.R'"
//AddButton.setOnClickListener(this);
}
}
XML layout file:
<?xml version='1.0' encoding='utf-8' ?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/LayoutRoot"
android:layout_height="match_parent"
android:layout_width="match_parent"
android:orientation="vertical">
<TextView
android:id="#+id/txtFirstNum"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:text="#string/strFirstNum" />
<EditText
android:id="#+id/edtFirstNum"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:text="" />
<TextView
android:id="#+id/txtSecondNum"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:text="#string/strSecondNum" />
<EditText
android:id="#+id/edtSecondNum"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:text="" />
<Button
android:id="#+id/btnAdd"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:text="#string/strAdd"
android:gravity="center" />
<TextView
android:id="#+id/txtResult"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:text="" />
</LinearLayout>

I resolved the issue by deleting the bin folder and recompiling using the AIDE App.

The R class is code-generated for you by the Android build tools when you build your project. This means there are four possibilities:
You have not tried building the project yet, in which case, try that.
Eclipse doesn't think it needs to build the project for some reason -- try Project > Clean from the Eclipse menu (only relevant if you are using Eclipse, of course).
There is some bug in your manifest or one of your resources that is preventing R from being built. There should be Eclipse error indicators for this.
You do not have an android:id attribute in your layout, and therefore there is no R.id available.

Please make sure the xml file you pasted is called main.xml and under layout folder.
And try to generate the R file again.
That may help.

For those using AIDE having issues referencing Id, try deleting the "gen folder" located in the bin folder and recompile. The problem is the R.java class did not create a constructor called Id. So deleting the gen folder containing the R.java class and recompiling solves this issue.

You must add id to a component in the XML file. Like this:
android:id="#+id/buton1"
Now can you click mainActivity.java and write code "R.id." you a see hint to write "buton1" and no error of "id"

Android problem

Hi iam working on android getting the following problem for my login but i didn't got my mistake... The error notice is the application has been terminated unexpectedly
my code is
package layout.program;
import android.app.Activity;
import android.os.Bundle;
public class Tablelayout extends Activity{
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.tablelayout);
}
}
tablelayout.xml
<?xml version="1.0" encoding="utf-8"?>
<TableLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TableRow android:id="#+id/tableRow1" android:layout_width="wrap_content" android:layout_height="wrap_content">
<TextView android:layout_height="wrap_content" android:text="TextView" android:id="#+id/textView1" android:textAppearance="?android:attr/textAppearanceMedium" android:layout_width="wrap_content"></TextView>
<EditText android:id="#+id/editText1" android:layout_height="wrap_content" android:layout_width="fill_parent">
<requestFocus></requestFocus>
</EditText>
</TableRow>
</TableLayout>

Try Cleaning your Project..
By Selecting the Project and then go to top project option and then select clean.
and then select OK..
Sometimes Changes are not made in R.java...Thats y this error comes

Your code is working fine at my end..please look in your code if there is anything which is causing the exception..Try to debug with debugger....

There's nothing wrong with your code or xml, so it has to be an error in your manifest.
As this application is just a stub, why not do this:
Create a new Android project, call it anything you like.
Call the activity 'TableLayoutActivity'
Put your tablelayout.xml into the layout folder.
Change the automatically generated code in TablelayoutActivity.java to set the content view from setContentView(R.layout.main) to setContentView(R.layout.tablelayout)
This should work, then have a look at the manifest in the new project, to see where you went wrong in your original project.

change the class name and try again,also check if the activity name mentioned in the android manifest is correct.