I'm trying to separate some of my java in a few different files.
I have my main class:
public class StartPage extends Activity {
...
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_start_page);
}
...
}
And then I have this other class that I'd like to run on the same layout:
public class part_settings_session extends Activity {
...
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_start_page);
Toast.makeText(getApplicationContext(), "This is from settings", Toast.LENGTH_SHORT).show();
}
...
}
But I'm not able to see that Toast happen anywhere or at any time. Is there a way to make both of these classes work in two separate files? This is to organize scripts for my own sake.
Two Activities can not be visible at same time and here in your code you have defined two Activities with same layout. Your code is fine but to see both activities working, you have to manually start next activity. Below code will help you. This code will start Next Activity 3 seconds after loading First Activity.
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
startActivity(new Intent(StartPage.this, NextPage.class));
finish();
}
}, 3000);
in your onCreate() for the 2nd class, put a Log.d("part_settings_session", "onCreate"); and see if the onCreate ever gets called in the first place. (Since they are using the same layout, it might be difficult to see if you are 'actually' creating an instance of THIS class.
My guess is that you might not even be creating an instance of the part_settings_session class. And without logging it is pretty hard to tell that.
Here is a nice Activity base class that will log all life-cycle events for you
https://github.com/douglascraigschmidt/CS282/blob/c5cf5c4808ea082988ab87c00eeade4837eac967/assignments/assignment1/src/edu/vandy/common/LifecycleLoggingActivity.java
Related
I am trying to make a simple QR Code scanner and run well if the result shows in the MainActivity. But when I'm trying to generate new Activity as a result, it can't show. Would you like to help me with this problem? Thank you.
Here is the result of the scanner code in the scanner.java:
#Override
public void handleResult(Result rawResult) {
startActivity(new Intent(getApplicationContext(),ResultActivity.class));
ResultActivity.scanText2.setText(rawResult.getText());
onBackPressed();
}
And here is the code of my new Activity for showing the result:
public class ResultActivity extends AppCompatActivity {
public static TextView scanText2;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_patient);
scanText2 = (TextView) findViewById(R.id.scanText2);
}
}
There are a lot of issues with this:
You are launching PatientActivity, not ResultActivity in handleResult()
You are trying to set the value of a TextView in another Activity with this code:
ResultActivity.scanText2.setText(rawResult.getText());
This is an absolute no-no. Pass the data to ResultActivity as an Intent extra when you launch it. You cannot access the views of another Activity like that.
You expect that ResultActivity.scanText2 will contain a reference to a TextView, but at this point it will only contain null. The reason is that it takes some time for ResultActivity to actually start and call its onCreate(). You have not accounted for this timing in your code. To solve this problem, just see (2) above.
Also, you should have gotten a bunch of crashes with useful messages in your logcat. In the future please look there to solve problems and/or post the messages with stacktrace in your Stackoverflow questions.
im sorry for the long question, but i could really use the help
so I've been trying to make a camera app for this school project that i have. i'm really new to coding in general, and i don't really know much about Java. i decided to use the CameraKit library by Furgle to help me with this. they say all i have to do is include
protected void onResume() {
super.onResume();
CameraView.start();
and
#Override
protected void onPause () {
super.onPause();
CameraView.stop();
}
i should be able to start and stop the camera preview im trying to create.
however, when i added this code to my main activity, i got the following:
non static method 'stop()' / 'start()' cannot be referenced from a static context
I've tried a few things like trying to create an object of the class and calling the method from that (i'm not completely sure if i said that right or not)
#Override
protected void onResume() {
super.onResume();
CameraView main = new CameraView()
main.start();
when i try to run that, i get:
cannot resolve constructor CameraView()
I also tried to create instances of the class called "CameraView" which is where the method "start();" and "stop();" are. sadly i have not been able to get anywhere with that.
the point is i tried everything that i could understand but any help would be greatly appreciated.
after looking into the code for the library, i saw that neither the start method or the stop method within the CameraView class are declared "static". so i really don't see where the problem is coming from and how to overcome it
Assuming the tutorial you're following is this one https://github.com/gogopop/CameraKit-Android#usage ...
When they say that "all you have to do" is add this code:
#Override
protected void onResume() {
super.onResume();
cameraView.start();
}
#Override
protected void onPause() {
cameraView.stop();
super.onPause();
}
They're speaking to more-experienced developers. The part they're leaving out is where does cameraView come from?
Well, the first step is to include a <CameraView> in your layout. But even after that, you need to find it and assign it to a cameraView variable. So really, you need all this:
public class MainActivity extends AppCompatActivity {
private CameraView cameraView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); // `activity_main.xml` must have a `<CameraView>` tag with id `camera`
cameraView = (CameraView) findViewById(R.id.camera);
}
#Override
protected void onResume() {
super.onResume();
cameraView.start();
}
#Override
protected void onPause() {
cameraView.stop();
super.onPause();
}
}
I am trying to define global objects using the application class.
I therefore define the following class.
public class MyApplication extends Application {
private MyObject myObject=new MyObject();
public MyObject getMyObject(){
return this.myObject;
}
}
Then, I use it in an activity, but I get an error (Cannot resolve method getApplication()):
public class AnActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_mood);
Button buttonMusic=(Button) findViewById(R.id.button5);
buttonMusic.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
MyApplication myApplication = ((MyApplication)this.getApplication());
Toast.makeText(MoodActivity.this, "playing music", Toast.LENGTH_SHORT).show();
}
});
}
}
I have no clue why I get this error, as it for example works when calling the getApplication() in another activity.
I'm pretty new to Android and Java, so please excuse the ingenuity of the question.
UPDATE
Then I do MyObject myObject=myApplication.getMyObject(); and I don't get any compilation issue but the app dies as soon as I get in that activity.
As I understand it is not advised to use the Application class for such use, what would be a good alternative?
You're getting this error because you call this.getApplication() inside the View.OnClickListener. Because of this, this now references the listener and not the activity.
To do what you need, just create a Context object outside of the listener in your activity's onCreate method and assign this to it. And, inside the listener, use context instead of this. Something like this :-
public class AnActivity extends Activity {
Context context;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_mood);
context = this;
Button buttonMusic=(Button) findViewById(R.id.button5);
buttonMusic.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
MyApplication myApplication = ((MyApplication)context.getApplication());//Changed "the" to "context"
Toast.makeText(MoodActivity.this, "playing music", Toast.LENGTH_SHORT).show();
}
});
}
}
Edit after question update :-
Instead of using the application class, use static objects to achieve global variables. static objects are independent of objects and can be referenced using the class that they belong to. For example, if you define a static variable in your MainActivity.class and name it testObject, then it can be accessed using the following code regardless of your current activity :-
YourObject object = MainActivity.testObject;
Unless you have a specific reason for extending the Application class in Android you probably shouldn't. For reference, look at the note in the documentation for this: https://developer.android.com/reference/android/app/Application.html .
If you are trying to create an object that you can use in your Android app, simply do that as you would in Java:
public class MyObject {
//Your stuff here
}
If there is a reason that you're specifically wanting to extend the Application class then perhaps there's more that people can do to help you if you explain what you're trying to do. I just don't necessarily see a need to go through all that complexity based on your example :)
Change this to AnActivity.this.
Inside the code below the meaning of this changes from AnActivity to View.onClickListener as it is another object and inside those braces you are in the scope of the click listener class
new View.OnClickListener() {
public void onClick(View v) {
MyApplication myApplication = ((MyApplication)this.getApplication());
Toast.makeText(MoodActivity.this, "playing music", Toast.LENGTH_SHORT).show();
}
}
So the code above should become
new View.OnClickListener() {
public void onClick(View v) {
MyApplication myApplication = ((MyApplication)AnActivity.this.getApplication());
Toast.makeText(MoodActivity.this, "playing music", Toast.LENGTH_SHORT).show();
}
}
You can read a bit more about it here
Have some problem with android finish() methods.
I have one parent-class activity. Lets call it ParentActivity. All other activities in my project extends ParentActivity. Each time on ParentActivity.onCreate there are some statement, and I want to stop activity from executing if it fails. But when I call finish() in parent, I cant stop executing onCreate method on its child. Something like that:
public class ParentActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (!someStatement) finish();
}
public class Test extends ParentActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.d("TAG", "I dont want this code!");
}
}
Surely, I can just verify in parent activity its status each time, but I dont think its a good idea.
public class Test extends RexActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (isFinishing()) return; /// It works - but it bad :(((
Log.d("TAG", "I dont want this code!");
}
}
Can I somehow stop executing onCreate method on child activity from its parent? Many thanks for any help!
I'm not sure if I got your question right. As you have some grammatical issues.
The onCreate statements are always executed. You can either have a Boolean in ParentActivity to stop the code from executing in ChildActivity#onCreate().
You can try making your onCreate() code more modular by dividing it into functions so that it's not called.
Let me know what works for you.
Best option is to Use finish() in your splash screen just before you create your second activity,
First off, I did post this to the android google group first but its moderated and I'm not sure how long itll take to show up there so hoping someone here can help.
I created a simple app with a ListView following the ListActivity
examples I found on the net.
The app has 2 activities with the first having a button to create the
second. When i hit the close button on the second activity I would
like it to release its memory (or at least allow it to be garbage
collected). Currently it will never release.
I must be doing something wrong here because the MyListActivity never
gets released. Can anyone tell me if I am doing something wrong with
the way my activities are created/destroyed? or if my usage of the
ListView is wrong?
Thanks.
My App as a zip - http://www.mediafire.com/?l26o5hz2bmbwk6j
Screen Shot of Eclipse MAT showing the list activity never releasing
memory - www.mediafire.com/?qr6ga0k
public class MyListActivity extends ListActivity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.listlayout);
ListAdapter ada = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, GENRES);
setListAdapter(ada);
}
#Override
public void onDestroy()
{
super.onDestroy();
System.gc();
}
public void ClickHandler(View target)
{
switch (target.getId())
{
case R.id.LL_Btn1:
finish();
break;
}
}
private static final String[] GENRES = new String[] {
"Action", "Adventure", "Animation", "Children", "Comedy", "Documentary", "Drama",
"Foreign", "History", "Independent", "Romance", "Sci-Fi", "Television", "Thriller"
};}
public class MainActivity extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
public void ClickHandler(View target)
{
switch (target.getId())
{
case R.id.M_Button01:
Intent intent = new Intent();
intent.setClassName(MyListActivity.class.getPackage().getName(), MyListActivity.class.getName());
startActivity(intent);
break;
}
}}
Have you tried getting rid of System.gc() and see what happens? Calling System.gc() is merely telling the VM to initiate garbage collection - there is no guarantee when it will be done.
Not sure if this will help, and its not generally recommended to do this, but the following will kill your process in onDestroy():
System.runFinalizersOnExit(true);
android.os.Process.killProcess(android.os.Process.myPid());
Put that in the onDestroy method. Now this may actually kill your main process if called from a child activity (havn't tested it).
WARNING: I generally don't recommend doing this as its a "hackly" way of doing it, but if you just need your app (or activity) to close upon exit then this will work. You still need to debug to find out why your app is staying open and eating memory.
Eclipse MAT was the cause. New Android Studio doesn't cause these problems.