How can I manipulate another Activity's XML file components (like EditText) from main Activity, in terms of setEnabled() etc. Do I need to instantiate a field MySecondActivity inside MainActivity class and manipulate it via methods i create in that second Activity?
I tried without doing that. I instantiated EditText editText = findViewById(R.id.edit_text) in onCreate() method at Main Activity which is contained in the second Activity's xml, but that gives me null pointer exception.
By android design, each Activity like different application, have to work independed as it can. You should send parameters as extras in intent and do your work it that activity.
But you can do it, for example linking activities by static field:
ActivityA {
public static ActivityB instance = null;
onClick() {
startActivity(new Intent(this, ActivityB.class));
}
}
ActivityB {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ActivityA.instance = this;
}
}
After that you can access AcitivityB from ActivityA by "instalce", but again, this is not the right way!
Related
I have two activities (A and B). Activity A calls activity B. Activity B has Back (Up) button like this:
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
Now when this UP button is pressed, onCreate of activity A is again called. In the activity A, there is a classId variable (which I got from an Intent) which I want to retain. For this I have following code in my onCreate of activity A:
if (savedInstanceState == null)
{
Intent intent = getIntent();
classId = intent.getIntExtra("CLASS_ID", 0);
}
else
{
classId = savedInstanceState.getInt("CLASS_ID");
}
I have also overriden the onSavedInstanceState method:
#Override
protected void onSaveInstanceState(Bundle savedInstanceState)
{
savedInstanceState.putInt("CLASS_ID", classId);
super.onSaveInstanceState(savedInstanceState);
}
I am following this SO answer:
onCreate being called on Activity A in up navigation
The problem I am facing is that when I come again to activity A by passing back button in activity B, onCreate gets called and I found savedInstanceState to be NULL.
Edit:
Is there any other way to save my classId variable so that when I return again to activity A, I can use that?
Edit 2
If I set launch mode of my activity A to SingleTop in the manifest file, my issue gets resolved. Is it the right approach?
You should not suppose that onSaveInstanceState called each time you go to next activity.See the docs
This method is called before an activity may be killed so that when it comes back some time in the future it can restore its state. For example, if activity B is launched in front of activity A, and at some point activity A is killed to reclaim resources, activity A will have a chance to save the current state of its user interface via this method so that when the user returns to activity A, the state of the user interface can be restored via onCreate(Bundle) or onRestoreInstanceState(Bundle).
You may further consult with official docs here
Try this
public class SingletonHolder {
//your id here as what data type you want
private static SingletonHolder instance;
public static SingletonHolder getInstance() {
if (instance == null) {
instance = new SingletonHolder();
}
return instance;
}
//set getter setter here
}
If not successfull feel free to comment
I changed the launchMode of the activity A to singleTop in the mainfest file like this:
android:launchMode="singleTop"
I followed this question on SO: Setting launchMode="singleTask" vs setting activity launchMode="singleTop"
By using this approach, activity A is not destroyed and when I just finish the activity B or click UP navigation in activity B, the existing instance of activity A is launched again.
I have somthing like that:
public class A()
{
private Button myButton;
public void setMyButton(Button myButton)
{
this.myButton = myButton;
}
public Button getMyButton()
{
return myButton;
}
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button = (Button) findViewById(R.id.button);
setMyButton(button);
}
public class B()
{
public void exampleMethod()
{
A aObject = new A();
Button button = aObject.getMyButton();
}
}
Button in class B is always null. I tryied that:
In class A
public Button myButton;
In class B
A aObject = new A();
Button button = aObject.myButton;
but it is not working too.
I am sure that first is button initiate, then geting button reference. I checked that using logs.
I don't know what is going on, becasue "getMyButton" in class A work fine. How can I get reference of button from class A in class B?
What is the best way to do that?
Looks like you are creating new java object of your activity on your own. Please try to get existing object of an created activity; so that you will get activity context and activity properties as well.
The button is always null because its set in onCreate, which is not automatically called. Let me guess, A is supposed to be an Activity subclass, based on the signature, right? In that case you're doing things really wrong.
*You cannot create an Activity via new, it won't be properly initialized.
*Accessing views of an Activity like that is really weird. It makes more sense to pass the view into B, as B is likely owned by A. If the Activity A doesn't own B, you're probably doing something really wrong. Pretty much if you need to do this you've probably misarchitected something.
The way that you are doing will only works in JAVA and not in ANDROID.
Its because of ACTIVITY class. Activity class reference will be created only when its life cycle is created and you cannot pass the UI elements of one activity to Another.
As the button is associated with the 'A' Class in your case and if you want this in Class 'B' you have to start Activity and its life cycle and also setContentView(R.layout.activity_main);
Other way is get the data that you want from any class and publish the value in 'A' class itself. this can be done by startActivityForResult();
I want to check some condtiton before the main activity starts and based on test result i have to either start a new activity or continue the same activity. How to do this?
you can check it in your OnCreate() method. It is called when your activity start.
onCreate(...){
....
if(want this){
//continue;
}else{
// start new activity
}
}
The default Activity to start is set in the manifest, so a better approach to your problem would be to use fragments. Keep in mind that fragments are faster/lighter, so instead of using Application as a "decision" class to start activities (bad practice), use your main activity. In your onCreate() method, check for your condition and attach the needed fragment.
I am using java annotation to handle this case:
Create the Annoation class
Create CustomContext.java with a startActivity method in it
Create the Interceptor.java
Create a class which implement Interceptor like this (named DemoInterceptor.java here)
Declare a static variable of DemoInterceptor in your activity. and the demo Activity should like this then, start the activity via the custom startActivity in step #2
enjoy and let me know if you have any further question.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(startNewActivity) {
// TODO Fire off intent to start new activity
finish(); // Closes the current activity
return;
}
// TODO Code for current activity.
}
startNewActivity is a boolean indicating whether to launch a new activity or not. It should be assigned a value depending on your condition.
This is unlikely but it would potentially save me a lot of time to re-write the same code.
I want to implement a UI using alert-type service (like Chathead) yet I'd still like to use my fragments. Is it possible? I know I can add views to the window but fragments?
Fragments are part of the activity, so they cannot replace activity. Though they behave like activity, they cannot stand themselves. Its like view cannot itself act like activity.
From Android Developers:
A Fragment represents a behavior or a portion of user interface in an
Activity. You can combine multiple fragments in a single activity to
build a multi-pane UI and reuse a fragment in multiple activities. You
can think of a fragment as a modular section of an activity, which has
its own lifecycle, receives its own input events, and which you can
add or remove while the activity is running (sort of like a "sub
activity" that you can reuse in different activities).
I hope it is helpful to you.
Well as people have pointed out you can't, but, you can always create
some sort of fragment wrapper.
For example purposes:
public class ActivityFragmentWrapper extends FragmentActivity {
public static final String KEY_FRAGMENT_CLASS = "keyFragmentClass";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getIntent().getExtras() != null) {
String fragmentClass = (String) getIntent().getExtras().get(KEY_FRAGMENT_CLASS);
try {
Class<?> cls = Class.forName(fragmentClass);
Constructor<?> constructor = cls.getConstructor();
Fragment fragment = (Fragment) constructor.newInstance();
// do some managing or add fragment to activity
getFragmentManager().beginTransaction().add(fragment, "bla").commit();
} catch (Exception LetsHopeWeCanIgnoreThis) {
}
}
}
public static void startActivityWithFragment(Context context, String classPathName) {
Intent intent = new Intent(context, ActivityFragmentWrapper.class);
intent.putExtra(KEY_FRAGMENT_CLASS, classPathName);
context.startActivity(intent);
}
}
You can start it like:
ActivityFragmentWrapper.startActivityWithFragment(context, SomeSpecificFragment.class.getCanonicalName().toString());
Of course if your fragment has another constructor you have to retrieve different
one, but that part gets easier.
No, Fragments can't exist without an Activity. They need an activity for their entry point otherwise they can't initiate their UI components and their lifecycle can't go beyond onAttach and onCreateView
I know that I can pass some values between Activities using intent.
However, if I want to pass whole Activity to another Activity I think it is not good approach.
Is there another way to do that?
I have Settings Activity in which I am changing some Colors. So after I come back to my Main Activity I would like to apply those colors. To do this, I need access to MainActivity fields after I change Color value, so inside PreferenceActivity. In other words, I want to have access to Main activity fields from PreferenceActivity class. Any ideas?
You should be using a SharedPreference and then accessing that in your main activity. I recommend you reading up at http://developer.android.com/guide/topics/ui/settings.html because it seems like you are implementing your settings activity incorrectly. The part you might be specifically interested in is the "Read Preferences" section. However, I strongly suggest you read through the whole thing and then implement your settings the proper way.
Updated answer with the 3 different ways (that I can think of):
1) Start your preference activity using startActivityForResult(), then in your onActivityResult() access the SharedPreference and make your necessary changes. See here
2) Register a SharedPreferenceChangeListener with your MainActivity, which will be called when any changes happen to your SharedPreference. See here for a detailed discussion. Also see my initial response.
3) In your MainActivity's onResume(), access the SharedPreference and then make your changes there. I do not like this method because you will be cluttering onResume() with more logic and you will also probably have to have a variable that keeps track of the state of the variable you are interested in.
I would personally go with option 2 because the callback was created for this exact purpose.
I think you could pass the value by using method putExtra(name, value).
And after you start new activity you can get the value you pass before by using method getStringExtra(name).
Shared preferences can be used. If you want your changes to be reflected right away add listener. Refer to SharedPreferences.onSharedPreferenceChangeListener. Its an easy way to do.
If you want to lots of changes required in many activity from you change in any one.
And access last modify data from all Activity and modify also.
for example.
Constants.java
public class Constants
{
public static String name;
}
In your MainActivity you have an editText.
MainActivity.java
public class MainActivity extends Activity {
private EditText yourName;
private Button btn;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
yourName = (EditText) findViewById(R.id.yourName);
btn = (Button) findViewById(R.id.btn);
btn.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
Constants.name = yourname.getText().toString();
Intent intent = new Intent(getApplicationContext(),Activity2.class);
startActivity(intent);
}
});
}
In your Activity2 you have an TextView and that getting value which you enter in MainActivity.java without pass in Intent.
Activity2.java
public class Activity2 extends Activity {
private TextView yourName;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
yourName = (TextView) findViewById(R.id.tv_yourName);
// directly use ferom serializable class
yourname.setText(Constants.name);
}
like that you use many values from all activity and modify from all activity.