I am trying to create a simple button example, but when I add this code:
mButton = (Button) findViewById(R.id.button1);
it wont update my R.id file. I've tried everything including making sure automatic build is on, cleaning the project, and updating the SDK. This happens in both 1.6 and 2.2 projects.
Here's what full code is looking like:
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class NewTest extends Activity {
Button myButton;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
myButton = (Button) findViewById(R.id.button1);
}
}
findViewById is looking at the R.id file for the location you refer to.
Your code will not cause the file to update as it is only looking for the button.
Creating the button in your layout will cause the R.id file to update.
<Button
android:id="#+id/button1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Button One"/>
As you are using findViewById in context, and the view for the current context is main.xml, the above button example will need to be inside the main.xml file. Otherwise if you had another button with the same name in another .xml layout, the entry would be made in your R.id file but your code would give you a null pointer exception, because the button doesn't exist in the context you are trying to reference it from.
Make sure you have proper import for your app's R class in your Activity:
import your.app.package.R;
UPDATE: this implicit import is only needed if your Activity class is not in the root of your.app.package package.
Save your project before using R.id.something
Since you are using XML based Layout make sure that you have android:id attribute in the main.xml file with "#+id/button1" as its value.......
It wouldn't update the generated R.java file when you just refer to an existing id.
It only updates when you add a resource. button01 must already exist in one of your .xml files, otherwise your 'findViewById(R.id.button1)' wouldn't compile.
I had the same problem using API 19 with the layout editor set to API 15 while trying to follow the NotePadV1 tutorial. I couldn't get the R.id.text1 to compile from the notes_row.xml file.
Originally, I had just pasted text into the xml file to generate the layout. After unsuccessfully trying deleting R and a Clean, I tried deleting the notes_row layout entirely. When I recreated the layout, I used the graphical interface to add the properties of the TextView object, just the Id #+id/text1, width and height. Then I did a Clean and compile. It worked.
Related
I have one problem with the comments in Android Studio.
My template file (File Header) Is like this:
/**
* Created by ${USER} on ${DATE}.
*/
When I create new class, or Interface my comment header gets automatically generated, and this works.
But when I generate: activity, fragment, application, services, the comment does not generate. I really do not know where is the problem.
Here is the Activity template description. But when I create new Activity, the comment does not appear, and every time I need to retype it.
package ${PACKAGE_NAME};
import android.app.Activity;
import android.os.Bundle;
#parse("File Header.java")
public class ${NAME} extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
}
Thanks!
To generate comments type /** above the method name and press enter. You can also use a tool under Android Studio menu:
Tools > Generate JavaDoc
I'm new to Android programming, and I'm trying to make a simple button which displays a toast notification when clicked.
I tried to initialize a button called "button" in my MainActivity like so:
public class MainActivity extends Activity implements View.OnClickListener {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button =(Button)findViewById(R.id.button1);
button.setOnClickListener(this);
}
public void onClick(View v){
Toast toast = Toast.makeText(this, "Click Me", Toast.LENGTH_LONG);
toast.show();
}
}
Also, here is activity_main.xml:
<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">
<Button
android:id="#+id/button1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="#string/button1">
</Button>
</RelativeLayout>
UPDATE: findViewById now works fine after importing android.R. However, this created a new error when I call setContentView(R.layout.activity_main);
Okay a bit of background here. strings.xml is for defining pieces of text. For instance the text that might go on a button (but this does not define the button itself).
The button is going to have to be defined in a layout file in the res/layout/ directory. Yours is likely called activity_main.xml.
You'll need to create a button element in this file and assign the id to something descriptive. This kind of id is what findViewById is going to search on.
An example:
<Button
android:id="#+id/thebuttonsid"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_marginTop="96dp"
android:text="#string/button1" />
You can get a handle to this button like so:
Button button = (Button)findViewById(R.id.thebuttonsid);
Notice how I set the text to #string/button1? This is what the strings.xml file is for. However the layout files in the layout directory are where you define controls like buttons.
The button's ID name is same to the button's text name. You'd better change any one to other name.It must be work.
I would clean the project and build again. Or reimport the project. Eclipse is ... just hard to use. Try to use Android Studio.
When there is some "mismatch" with resources cleaning a project is a good advice. IN the past it was even more so.
Next what I would check if your resources compile as such. You might have an error somewhere in your resources, therefore the R does net get compiled and any reference to R.id.* is not valid.
Eclipse is not recognizing R.id. I just started learning Android so please help me out here.
import android.app.Activity;
import android.os.Bundle;
import android.widget.EditText;
public class SecondappActivity extends Activity {
EditText ed;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ed=(EditText) findViewById(R.id.b1);
}
}
it is saying id cannot be resolved or is not a field
Check your xml file and make sure it doesn't have any error. Looks like there is a problem with generating R file. It can be caused by errors in xml.
Check for any errors in your xml files or your res folder. Clean and rebuild project. It will work
What does your main.xml file look like?
There is nothing wrong with your java code. Assuming all your imports are working.
Chances are bn1 is either not in that layout. Or you are not adding the '+' in you android:id field to make sure this goes into the R.java file.
Put
import YourWholePackage.R;
in import segment.
I have the same issue :/ I am just getting into android development and already stuck. This is my code:
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
EditText nameEditText = (EditText) findViewById(R.id.nameEditText)
}
}
Nothing fancy, just one edittext field and one button, no errors in activity_main.xml. But when I am typing findViewById - its not even available in autosuggestion list.
Thanks
Why can't I use setContentView(R.layout.main) in last line without setContentView(tv)? Please explain this to me.
package com.mue.helloworld;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class HelloWorldActivity extends Activity
{
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView tv = new TextView(this);
tv.setText("Hello, Android i am suvankar");
setContentView(tv);
}
}
You have to define the textview in the R.layout.main ( a xml file) this file contains the information of the objects in the activity.
if you are using eclipse you can simple drag and drop a textview, just open the main file.
(folder res -> layout -> main.xml)
then yo have to call it in your program:
setContentView(R.layout.main);
TextView tv = (TextView) findViewById(R.id.tv); //<-- yo have to use the same ID that is in the main.xml file
and then you can set the text. all of this in the oncreate function.
tv.setText("Hello, Android i am suvankar");
Well, I hope I've helped. is my first response here
You shouldn't call setContentView() twice in your onCreate. Either call setContentView(R.layout.main) or call setContentView(tv) but not both. I would prefer the first of the two... but you need to make sure the TextView is declared in your layouts XML.
Lets first try to understand what setContentView() method does. Basically setContentView() places your UI on your Activity. Now to create a UI component for your Activity, you can either use xml resource (e.g. R.layout.main) or you can obtain an instance of the UI component in your code and dynamically add it to your Activity. For example
TextView tv = new TextView(this);
tv.setText("Hello, Android i am suvankar");
setContentView(tv);
In your case you created an instance of the TextView tv, set some text to it and added that to your Activity. Here you dont need to use setContentView(R.layout.main). However if you have a xml layout (main.xml) in your layouts folder like the following:
<?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"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Hello World"
/>
</LinearLayout>
and at the bottom of your application you write setContentView(R.layout.main), your should see a black screen with Hello World written on it. This is because here you created a TextView instance, set some text to it, but did not place it to your activity by calling
setContentView(tv), rather you added a completely different layout resource. If you use setContentView(tv) and at the end of your onCreate() you add setContentView(R.layout.main) then again you will see Hello World instead of "Hello, Android i am suvankar" because at the end you replaced your UI resource. However, if you forget to add your xml resource and call 'setContentView(R.layout.main)' compiler will issue an error for not finding the xml resource specified.
Is there anywhere that I can find documentation on the scope of the XML files? I have an app I am currently working on and have been struggling with getting a feature to work and it seems that the problem I am having is that I am trying to access an element in an XML file that must be out of scope. To simplify the layout, my project has main.xml, sub.xml, main.java, and sub.java files in it. As you can probably guess, main.java works with main.xml and sub.java is working with the elements in sub.xml. Here's where the issue comes in, I have a TextView element that is created in main.xml that I would like to modify the text in, but the action that would trigger it will occur in sub.java. I can't figure out how to change it from sub.java, and I can't figure out how to move the element into sub.xml. The code I am using is pretty simple:
TextView titleText = (TextView) findViewById(R.id.myTitle);
titleText.setText(filePath);
I get a FC every time I run the app, but if I move the code into main.java, it runs flawlessly. If anyone can offer any ideas, or point me in the direction of some documentation that would explain what java files can access what elements in which xml files, that would be awesome! Sorry for the novel, but I'm just struggling to get the point across. Thanks.
try like this Bryan in Main.xml file it works with no issue...........Declare first & then Initialize it...
public class Main extends Activity {
static TextView tv;
static Button submit;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
tv = (TextView) findViewById(R.id.header_text1);
}
}
Activity.findViewById(int) only works if that view is in the activity's layout. So no, you can't refer to a view in main.xml because that layout doesn't apply to sub.
Do you have any TextViews in sub.xml called myTitle?
You can access the the textview of main.java(main.xml) in submain.java as follows
In main.java write the following code
static TextView titleText = (TextView) findViewById(R.id.myTitle);
titleText.setText(filePath);
and u can access this submain.java as
Main.titleText.setText(filePath);