In OOP, I can use the object to call its methods. So I want to do that in android using the same concept. However, it doesn't work. I used context to call the function updateLvl(int), but it said the method cannot be resolved. I want to know how can I use the context to call the method updateLvl?
public class MainActivity extends Activity {
private WebView webview;
SharedPreferences sharedPref;
SharedPreferences.Editor editor;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
sharedPref = this.getPreferences(0);
editor = sharedPref.edit();
webview = new WebView(this);
webview.getSettings().setJavaScriptEnabled(true);
webview.addJavascriptInterface(new WebViewJavaScriptInterface2(this), "app");
public void updateLvl(int newLvl){
sharedPref = this.getPreferences(0);
editor = sharedPref.edit();
int be4Level = sharedPref.getInt("currLevel", 1);
if (newLvl >= be4Level){
editor.putInt("currLevel", newLvl);
editor.commit();
}
}
}
class WebViewJavaScriptInterface2{
private Context context;
/*
* Need a reference to the context in order to sent a post message
*/
public WebViewJavaScriptInterface2(Context context){
this.context = context;
}
#JavascriptInterface
public void openLvl(int lvl){
context.updateLvl(lvl);
}
}
you need to cast your context as MainActivity because your MainActivity class has updateLvl method not Context class hence compiler will show you error while applying static binding
#JavascriptInterface
public void openLvl(int lvl){
if(context instanceof MainActivity) // add safety check if required
((MainActivity)context).updateLvl(lvl);
}
The Context is not the instance of your WebViewJavaScriptInterface2 but a class of the android system (as well as Activity).
One way is to cast the context to the activity as Pavneet suggested. But this has the flaw that you can not be absolutely sure in your WebViewJavaScriptInterface2 that is is instanced from the right activity. Also you can use it just from one activity if you cast it to that one.
A cleaner way would be to define a callback interface, implement that interface in your activity (or multiple activity) and pass that callback interface into the WebViewJavaScriptInterface2.
This might help someone.
new Handler(Looper.getMainLooper())
.post(new Runnable(){
#override
public void run(){
updateLvl(lvl);
}
});
Related
I've read a few questions about this, but I wasn't happy with the answers, so I decided do ask about my particular example.
I'm developing and Android App that has a Settings screen with a few configurable integer parameters. All these parameters have a maximum and minimum value. Therefore, everytime the user sets a new value for those parameters, I want to validate them. If the new value is out of the defined bounds, I want to show a Toast informing the user of what went wrong.
On the other hand, because in some situations in my App the user can "spam" a button that may show a Toast, in order to avoid having Toast showing repetedly for a while, I created an Application class with a static Toast that is shown everytime I want to show a toast:
public class MyApplication extends Application {
private static Toast toast;
public static void showToast(Context context, String string){
//(...)
}
}
Back to the Settings page, here's how I implemented it:
public class SettingsActivity extends PreferenceActivity {
private Context context;
static SharedPreferences sharedPreferences;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
context = this;
sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
getFragmentManager().beginTransaction().replace(android.R.id.content, new SettingsFragment()).commit();
}
public static class SettingsFragment extends PreferenceFragment implements SharedPreferences.OnSharedPreferenceChangeListener {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
setListeners();
}
public void setListeners() {
setListenerA();
//(other listeners to other settings)
}
private void setListenerA() {
findPreference(KEY_PREF_A).setOnPreferenceChangeListener(
new Preference.OnPreferenceChangeListener() {
#Override
public boolean onPreferenceChange(Preference preference, Object newValue) {
boolean isEmpty = newValue.toString().isEmpty();
//(other validations)
boolean isValid = !isEmpty; //&& (other validations)
if(!isValid){
if(isEmpty){
MyApplication.showToast(context, MyApplication.getResources().getString(R.string.toastPreferenceNullValue));
} else if(isAnotherReasonToFail1){
// another Toast
} // else if(other reasons to fail)
}
return isValid;
}
}
);
}
}
}
And here are my problems: MyApplication.getResources() is a non-static method and cannot be called from the static context of class SettingsFragment. Also context is not static (as it should not be) and can't also be referenced there.
I need to show that Toast because otherwise the user wouldn't have a clue why his settings weren't being applied. On the other hand, I need the error message to be stored in the strings.xml file, not only because that's how you do it, but also for future multi-language purposes.
I am not familiar with how Fragments work, and I made the Settings screen like this after reading a few articles (like this one) and some questions here. There might be a different way to make a Settings screen that allows me to do what I want, I just don't know any.
Can someone suggest an approach that fits my problem?
Thanks
EDIT: emerssso solved the resources part. Now the problem is only how to call the Toast without having a context.
Fragment has a getResources() method that is equivalent to calling Application::getResources(). The only caveat is that you have to make sure that the fragment is attached to an activity (i.e. getActivity() != null) or you risk throwing an exception.
See: https://developer.android.com/reference/android/app/Fragment.html#getResources()
More generally, getActivity() can be used to get a valid context whenever the fragment is attached to the activity, as Activity is an implementation of Context.
If you want to have a context reference even after a fragment has detached, you can store a reference to getActivity().getApplicationContext() safely in the fragment for later use, but this is probably not ideal.
I have an Activity in whose onCreate() method i call a Utility function.
This utility functions requires a callback class instance as a parameter, in which it returns the info that i need. this is:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Utility.functionA(new functionACallBack() {
/**
*
*/
private static final long serialVersionUID = -7896922737679366614L;
#Override
public void onResponse(String error) {
((MyActivity) AppClass.getAppContext()).finish();
}
});
}
Once I have obtained that info, I want to close the activity. so i called finish() from inside the anonymous class that i created for the callback.
But the activity is not getting finished. I thought maybe i need to call finish() from UI thread so i did runOnUiThread(), in inside it also i tried calling finish(). But it just doesn't work.
Could someone please help me with this issue?
UPDATE:
I am storing APP context and then trying to use that but to no avail.
public class AppClass extends Application {
private static Context mContext;
#Override
public void onCreate() {
super.onCreate();
AppClass.mContext = getApplicationContext();
}
public static Context getAppContext(){
return AppClass.mContext;
}
}
Simply call something like this:
#Override
public void onResponse(String error) {
((Activity) context).finish();
}
As this is a static function, you'll have to be able to access your Context in a static way. You can save that as a Class variable, but you'll have to be aware about its handling as it might lead to memory leaks.
To avoid them, you can declare a class that extends Application and save here your context, so this way you won't ever have a memory leak.
Try using this code:
((Activity) ActivityClass.this).finish();
Remember, use the Activity class, not the Application one.
I have a non-activity class that needs to launch a new activity. Right now I just pass the current context as a parameter, but I would like to access the context statically if possible. I've already tried creating a new application (MyApplication extends Application), both as a new application and the main application, and neither worked. Any suggestions?
Current Code:
public class SharedFunctions {
public static void doSomething(Context context){
Intent i = new Intent(context, NextActivity.class);
context.startActivity(i);
}
}
The cleaner way to do it is to pass in a Context to each method. It's more typing, but it helps to make sure you're not leaking the reference.
Of course, if you really need static reference to it, you can just keep a static member in your SharedFunctions class and set it for each Activity.
onResume() and onPause() may be good places to set/clear it, but depending on your needs, you might want to change it. Just try not to keep references to old Activities.
public class SharedFunctions{
private static Context context;
public static void setContext(Context ctx){
context = ctx;
}
public static void doSomething(){
context.someContextFunction();
}
}
In each Activity:
protected void onResume(){
SharedFunctions.setContext(this);
}
protected void onPause(){
SharedFunctions.setContext(null);
}
create this class:
public class MyApplication
extends Application
{
private static Context context;
#Override
public void onCreate()
{
super.onCreate();
context = getApplicationContext();
}
public static Context getContext()
{
return context;
}
}
after that you must add this class to field name in application (Manifest)
<application
android:name="yourPackageName.MyApplication"
........
</application >
As a result you can call MyApplication.getContext() anywhere in your application and get the context.
hope, I help you.
I stuck at this issue many times and I passed the problem in different ways and I'm not sure that I made it in the right way.
I simplified the problem in a the following example. I know that I can pass only the data to the class but I do want to pass the editText cause I have this problem with more difficult UI controls.
mainactivity.java
public class mainactivity extends Activity {
public EditText clickEditText;
int count =0;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
newTxt();
}
public void newTxt() {
txt = new MyText(context);
txt.updateTextEdit("Main Activity");
}
}
myText.java
public class MyText
{
private Context _context;
// constructor
public MyText(Context context)
{
_context = context;
}
public void updateTextEdit(String str)
{
private EditText strEditText;
strEditText= (EditText)findViewById(_context.R.id.editTextClick); // ????
strEditText.setText(str + " and myTxt");
}
}
if you could explain me how to fix the updateTextEdit function. i passed the context of the main activity. How can I change the editText? Thank you very much!!!
If you really want to do this this way, you need to save a reference to Activity, not Context. Like this:
public class MyText
{
private Activity _activity;
// constructor
public MyText(Activity activity)
{
_activity= activity;
}
public void updateTextEdit(String str)
{
private EditText strEditText;
strEditText= (EditText)activity.findViewById(R.id.editTextClick);
strEditText.setText(str + " and myTxt");
}
}
and in newTxt() you will need to change:
txt = new MyText(context);
to:
txt = new MyText(this);
But wouldn't it be easier to just put this method inside your activity? Why do you want it in another class? If it really needs to be in another class, you could make that class an inner class of your activity and you would still have access to the activity's methods and member variables.
There's a similar question here
How to access Activity UI from my class?
You didn't say how you obtained the context, you should use this and get the mainactivity in the other class. not context.
then you can call runOnUIThread to perform UI updates.
I am currently working on an android project and I have an activity, lets call it MyActivity and this activity calls a standard Java class called MyClass.
I need MyClass to finish the MyActivity activity but I can't find out how to do this. I thought I might be able to pass the context to the standard java class and call context.finish() but this doesn't appear to be available.
How can I do this, thanks for any help you can offer.
You can pass the Context, but you will need to cast it to an Activity (or simply pass the Activity itself), although this in general seems like a bad practice.
The most secure solution uses listener and a Handler. It is complex, but ensures a non direct call to finish activity.
Your listener:
interface OnWantToCloseListener{
public void onWantToClose();
}
Class that should close activity.
class MyClass {
private OnWantToCloseListener listener;
public void setWantToCloseListener(OnWantToCloseListener listener){
this.listener = listener;
}
private void fireOnWantToClose(){
if(this.listener != null)
listener.onWantToClose();
}
}
When you want to close your activity you must call fireOnWantToClose() method.
public MyActivity extends Activity{
public void onCreate(){
final int CLOSE = 1; //number to identify what happens
MyClass my_class = new MyClass();
final Handler handler = new Handler(){
public void handleMessage(Message msg){
if(msg.what == CLOSE)
MyActivity.this.finish();
}
});
my_class.setOnWantToCloseListener(new OnWantToCloseListener(){
public void onWantToClose(){
handler.sendEmptyMessage(CLOSE);
}
});
}
}
This is secure because Activity is not finished directly by MyClass object, it is finished through a listener that orders a handler to finish activity. Even if you run MyClass object on a second thread this code will works nice.
EDIT: CLOSE var added I forget to declare and initialize this.
Pass the MyActivity to MyClass as an Activity. From there you can call myActivity.finish();
For example:
private Activity myActivity;
public MyClass(Activity myActivity){
this.myActivity = myActivity;
}
public void stopMyActivity(){
myActivity.finish();
}
And in MyActivity:
MyClass myClass = new MyClass(this);
This is risky, because you're holding a reference to an Activity, which can cause memory leaks.
If your java class is a nested inner class, you can use:
public class MyActivity extends Activity {
public static class JavaClass {
public void finishActivity() {
MyActivity.finish();
}
}
}
Otherwise you'll have to pass the java class a Context (i.e. pass it a reference to this, since Activity extends Context) and store it as a private instance variable.