Android :: What Is The Significance Of Context In Various Constructor Of Intent Class When Starting An Activity
Mar 4, 2010
I had come across a code snippet which calls for an activity without referring to any context. Before, i was considering that context is used to tell about the calling component. But as i came see that another component can be called without any reference to context, it makes me wonder what purpose it might be serving. please put some light on it.
Here is the code which calls for an activity without referring to 'context'
CODE:............................
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May 8, 2009
I'm posting this to share the lessons I learned while working with IntentService. IntentService has a single constructor that takes a string argument "name". The documentation has no description of what name is used for. In looking at the sources, I found that its only use is in naming the worker thread for the IntentService. This thread is named IntentService [name].
I initially implemented the constructor of the derived class to also take a String argument and passed it along to the derived class. This is wrong. This will cause the startService() call to generated a java.lang.InstantiationException in the application containing the service i.e. you don't get the exception in the application calling startService(). A clue to the actual problem is a little further up in the logs:"newInstance failed: no <init>()"
The derived class must have a Default constructor and that constructor must call super() passing a string for the name component of the worker thread name.
public class MyIntentService extends IntentService {
public MyIntentService() { super("MyIntentService");
} @Override
protected void onHandleIntent(Intent intent) {
// Handle events on worker thread here }
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May 14, 2010
I have an activity that when started needs access to two different ArrayLists. Both Lists are different Objects I have created myself.
Basically I need a way to pass these objects to the activity from an Intent. I can use addExtras() but this requires a Parceable compatible class. I could make my classes to be passed serializable but as I understand this slows down the program.
What are my options?
Can I pass an Enum?
As an an aside: is there a way to pass parameters to an Activity Constructor from an Intent?
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Mar 3, 2010
I have a class defined as
public class viewGroups extends ListActivity
Somewhere in the class I have
objItem = new clsContactGroups(context);
I am wondering what is advised to be used here? Which context?
I know four choices, but maybe there are others...
this
this.getApplicationContext()
this.getBaseContext()
this.getParent()
I use this Context to show a Toast. So I would like to show on the front-most view visible.
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May 4, 2010
For example, I have an activity that uses a utility class. I would like to be able to start an activity from the utility class and have the activity result sent back to the utility class.
The only way I could think of starting the activity was to pass the original activity to the utility class, so that the utility class could use the original activity to start the activity. The problem with this is that the activity is sent to the original activity, rather than the utility class.
I also thought of actually making the utility class an activity itself, but that would make using the utility class much more complicated.
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Jan 28, 2009
Can anyone tell me how to access context of a class which is not an activity?
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Aug 18, 2010
I have an activity class(Application Class ) which calls a service class(Service Class) and closes. The service class takes about 5 seconds to complete its task and calls a method which is present in another class(Callback Class). Now according to the result, the callback needs to notify the Application class.Once i get the callback from the service, I tried calling a method defined in the Application class. In this method i create a new intent of Application class and call startActivity(Application Class). But this is not working. Can anyone tell where i am going wrong and what can I do to solve this issue.
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Sep 18, 2010
I've adapted the GridInputProcessor-class of the 3D-Gallery ( http://android.git.kernel.org/?p=platform/packages/apps/Gallery3D.git;a=blob;f=src/com/cooliris/media/GridInputProcessor.java;h=91dfd4783be6b21ec8ff2518a5c244752570e90d;hb=HEAD ) so that it detects upward/downward swipes.
The detection of swipes works, but I now want to start another activity (or draw a bitmap on the currently displayed activity), but I seemingly can't use startActivity(mContext, myIntent), because the class declaration is public final class GridInputProcessor implements GestureDetector.OnGestureListener, GestureDetector.OnDoubleTapListener {so it doesn't extend Activity...
Can I still start an Activity through this class, or how would I go about doing this? I have also tried sending a broadcast, but this is also not "implemented".
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Jul 18, 2010
When starting two activities of the same class within the same instance using the flag REORDER_TO_FRONT, the new extra information of the second call does not override the first starting activity. Is this the desired behavior? How do retrieve the new extras?
For example: In the StubActivity, I have this code:
Intent i = new Intent(this, A.class);
i.putExtra("foobar",1); startActivity(i);
Activity A is displayed, and then this code is called upon a button press:
new Intent(this, A.class);
i.putExtra("foobar",2);
i.setFlag(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startActivity(i);
Activity A is re-displayed. Now check for the extras: int foobar = getIntent().getExtras().getInt("foobar")
Turns out that foobar = 1
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Jan 2, 2010
I have three classes one main-activity(named MainMap), one non-activity class(named MyItemizedOverlay), and one activity class(named AudioStream). I want to start AudioStream activity from non-activity class but i don't know how to.
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Jul 28, 2010
I've got two activities, one of them is called MyActivity. I want both of them to be able to use a function located in a class othat we may call MyClass. In MyClass, I try to use an intent to launch the activity AnotherActivity. Since the constructor takes a context as parameter, I simply tried to store a context from the activity in the constructor, and then use it when I try to create my intent.However, even thought none of the arguments are null (checked that with a simple if-statement), intent seems to be null and a NullPointerException is thrown. Why does it not work, and what can I do to solve the problem?
I'm quite new to Android and Java development, so please explain it as basic as you can.
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Jul 25, 2010
I want to specifically run the default Android browser for a given URL. I'm using this code: I also tried adding <uses-library android:name="com.google.android.browser" /> to the manifest. Am I missing something here? PS: I'm not interested in using startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.google.com"))) as it will list all the choices for the browsing Intent.
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May 20, 2010
I'm trying to create class with generics that will have ability to serialize its state using Parcelable interface.
The problem is that class has to contain constructor with single parameter - Parcel, but in my case I need to create class with additional parameters.
Besides, Parcelable.Creator doesn't allow to use generics.
Here is an example:
public class Sample<T> { ...
public Sample(Context ctx, SomeInterface iface, Parcel parcel) {...}
...}
What is the best practice to do it?
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Oct 10, 2013
I'm developing an app that uses google maps, but for some reason it crashed every time I try to call the constructor code from the map class.
main
[HIGH]import android.app.Activity;
import android.os.Bundle;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
[Code] ......
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Jul 21, 2010
I understand that Android Activities have specific lifecycles and that onCreate should be overridden and used for initialization, but what exactly happens in the constructor? Are there any cases when you could/should override the Activity constructor as well, or should you never touch it?
I'm assuming that the constructor should never be used because references to Activities aren't cleaned up entirely (thus hampering the garbage collector) and that onDestroy is there for that purpose. Is this correct?
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Nov 7, 2010
So I'm defining a class that sets a Drawable attribute in an object. The problem is that I can't access the getResource().getDrawable(int resourceId) method unless I have some Context.
So what I did was to send to that class an activity instance (let's call it "act") and then I did:
act.getResources().getDrawable(R.drawable.whellchair)
but, when executing that line it throws a NullPointerException.
When idea how to accomplish this?
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Jul 14, 2010
I'm just getting into Android development, and I have a question about communicating between a receiver class and an activity class. I'm very new to JAVA and Android so I hope I don't sound too stupid. I'm developing an application where I intercept an SMS message and then based on various elements of that SMS I might delete it once it's been saved to the inbox. I have a receiver class that intercepts the txt message, and I am also able to delete messages from my inbox with code in the activity class using a button at the moment. The problem I have is communicating between the receiver class and the activity class where the code to delete a message resides. I tried putting that code directly into the receiver class but as I'm sure most of you already know the BroadcastReceiver class doesn't seem to support what I need to delete messages. I've been searching for an answer to this for a while, but haven't been able to find anything. Honestly I'm not sure I know enough about JAVA and Android to even recognize a solution if I saw it.
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Sep 8, 2010
I'm new to Java and android development. In my application I need data which is accessible for a few activities. I've read that a good solution is to use Application class for this. So I use it like this:
public class MyApplication extends Application {
private String str;
public String getStr(){
return str;
}
public void setStr(String s){
str = s;
}
}
and I can access this variable from activity like this:........................................
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Oct 8, 2010
I have just started android. I just want to know that how can i call activity class from other java class. i just want to pass class object to activity class.
public class GsonParser extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
MagazineThread thread=new MagazineThread();
thread.start();
}
public GsonParser(JsonMagazineParser Obj)
{
}
}
and i am just doing like from other class. GsonParser obj=new GsonParser(this);passing obj to activity class.how can i achieve that.
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Jun 11, 2009
I have a problem and cant realize a reason. I have ClassNotFoundException when starting Intent i = new Intent(EventInfo.this, AndricoMap.class); i.putExtra("address", address); startActivity(i);
There are log and class below
CODE:.....................
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May 15, 2010
I wanted to know what is the difference between Context.startService(intent) and startService(intent) and does it matter which one is used?
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Nov 11, 2010
Sometimes I need to provide a Context object to call specific functions, such as
Intent intent = new Intent(context, MyClass.class);
in order to start a service
context.startService(intent);
Or, provide a Context object to do a query
Cursor cursor = context.managedQuery(uri, projection, null, null, null);
If this is done in a UI class which extends Activity, that's fine.
However, If I want to create my own utility class (a singleton) that doesn't extend anything and call these functions, I don't have necessary Context object. Now my workaround is to pass an activity reference while initializing the utility class and have that reference to call those functions. I'm wondering what's the correct way to do that. It should not be reasonable to have every class to extends Context so that it can call those functions.
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Mar 12, 2010
I am trying to get the value of a EditText in a dialog box. A the "*"'ed line in the following code, the safeNameEditText is null; i am assuming because the 'findVeiwById' is searching on the context of the 'AlertDialog.OnClickListener';
How can I get/change the context of that 'findViewById' call?
CODE:.................
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Sep 20, 2010
I am writing a very small app that just opens the camera app ready for video. I am able to get my code to work on an Android 2.2 emulator, but it will not work on my device, Motorola Droid 1 stock 2.2 FRG22D. Any ideas where I went wrong on this code?
CODE:............
It appears ThorstenW is correct. I would upvote your answer if I had enough rep. You can see from the logcat that com.android.camera could not be found and throws a fatal exception. Logcat below.
CODE:...................
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Dec 4, 2009
Need an example of how to create/start a new activity from the main activity. I have a button click event on the main layout. Originally I just used setContentView(R.layout.secondactivity); which brings up the layout but I don't think that is correct since the secondactivity class is not instantiated at this point yet. I have looked for such an example and can not find one.
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Mar 12, 2010
Basically i want to start Notepad application in android from my application , can i do this in android using runtime.exec() method of RuntimeClasss and assign it to a process and kill the process later.
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Apr 25, 2010
I have a map app which works fine when its stand alone but it causes an unexpected error when I try to add it as part of another app. My current app which extends Activity tries to launch the map activity with the following lines of code Intent m = new Intent(this, HomeSetter.class); startActivity(m); I also have the xml setup correctly <activity android:name=".HomeSetter" android:label="Screen 4"> </activity> <uses-library android:name="com.google.android.maps" /> </application> However when I try to launch it crashes everytime. I've tried searching the net but I've had no joy in finding a solution You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscribe @googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
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Oct 2, 2009
startActivity() displays the new Activity on top of the current one. But how to display it underneath instead? BTW, I'm starting an Activity from another application, if that makes a difference.
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Oct 14, 2010
I have four groups in a listview each with four url's I want to load in a webView. When the user select a url to goto I set a value like so;
if (position == 0) webb = webb +2;
{
Intent intent = new Intent(this, official.class);
startActivity(intent);
}
I then carryout the intent to move to the webView class where I have given each URL a value like so;
if (webb == 2) mWebView.loadUrl("http://yahoo.com");
if (webb == 3) mWebView.loadUrl("http://www.bbc.co.uk");
But the screen stays blank, if I state the value inside the official.class it works. How can I get this value to pass to another class based on the selection the user makes from the listview.
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Oct 16, 2010
I have been trying to get "getExtra" to work but without success, I have a listview with 4 choices which launch a webpage within a webView class, when the user selects the option lets say option 3 I want to pass the value of 3 to the webView class so that it will load the correct webpage, at the moment I get no errors, but the app force closes when I select the option, could this be due to having to announce this in the manifest? can somebody help with where I am going wrong. This is my intent
public void onListItemClick(ListView l, View v, int position, long id) {
if (position == 0) {
Intent intent = new Intent(this, official.class);
intent.putExtra("weburl", 3);
startActivity(intent);}
This is the official class:
public class official extends Activity {
int number = getIntent().getIntExtra("weburl", 0);
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if ((keyCode == KeyEvent.KEYCODE_BACK) && mWebView.canGoBack()) {
mWebView.goBack();
return true;
} return super.onKeyDown(keyCode, event);
} WebView mWebView;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.browser1);
mWebView = (WebView) findViewById(R.id.webview);
mWebView.getSettings().setJavaScriptEnabled(true);
if (number == 2) mWebView.loadUrl("http://bcafc.livewwware.co.uk");
if (number == 3) mWebView.loadUrl("http://www.bbc.co.uk");
mWebView.setWebViewClient(new HelloWebViewClient());
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