This is a real noob question I'm sure, but I am finding it quite perplexing.
Why an earth would you want to ever use intent.putExtra method to share information between classes in Android?
Let me explain. I am making my first Android app following the instructions from the developers guide (I am already at a moderate level with Java) and I am using some code that looks like this:
//Class field
//key holds string????? not fully understanding this...
public static final String EXTRA_MESSAGE = "self.anon.myfirstapp.MESSAGE";
//this method is activated by a button being pressed
public void sendMessage(View view) {
Intent intent = new Intent(this,DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.edit_message);
String message = editText.getText().toString();
//puts string message inside the string EXTRA_MESSAGE - why????
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);
}
OK firstly I want to point out I see what is happening and for the most part how it works (am just confused by the field declaration = "myClassPath" why?)...
BUT....
Surely it would be easier just to have a static field called:
public static String message;
then my method would look like this:
public void sendMessage(View view) {
Intent intent = new Intent(this,DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.edit_message);
message = editText.getText().toString();
startActivity(intent);
}
Then when my class DisplayMessageActivity needs the string message he just calls for:
String message = myClass.message;
That seems so much more straight forward. What is with the creation of the new string EXTRA_MESSAGE which just seems to hold the string message and why send it with the intent when my other class can access this info directly anyway -- and what does the field declaration with the "self.anon.myfirstapp.MESSAGE" mean? I can find no such folder or path leading to anything.
As someone else stated there are often situations (such as a screen rotate) in which the android system destroys and restarts the app - so all variable data is lost. It would only work consistently the way you suggest if your data is hard coded as a final variable. That is not the only reason for using intents though.
The great thing with using an intent to pass information is that you can use the intent not just to communicate with sub-activities within your own application but to any activity installed on that android system. For example you may want to launch an intent which starts the phone application and include as an extra the number that you want to call.
Perhaps a better question than yours though is "why would you not use intents to pass information?" The intent.putExtra() method allows you a convenient flexible and straight forward method to pass as much information as you like in a safe and secure way to any other activity.
intent.putExtra(EXTRA_MESSAGE, message);
works like a key value pair, when you want to retrieve the information from the intent you can simply do intent.get<type>Extra and get said information, in this case, intent.getStringExtra("self.redway.myfirstapp.MESSAGE'). its simply the key to retrieve the information, it does not have to be your entire classpath.
it could just as easily be intent.putExtra("message",message).
They are helpful when passing information that you don't necessarily want to reveal to another class but you do want it to be able to get that information in another manner from what i have found.
message = myClass.message It is not always certain that this will retain its value especially when it extends Android framework classes like Activity. When your activity is recreated(change of screen orientation) then message can lose its current value and be assigned a default value. myClass.message would work if message was a static field or else you would need to provide getter and setter methods for object of the Activity Class. Well creating objects of activity class is unheard of in my experience.
Related
I am on page 301 of this book and it is an example of an Activity getting "extras" from the intent that started it. I am fairly new to Java so maybe am missing something pretty obvious but...
I thought that when you declare a variable as "final" it meant that it doesn't change.
There is a line of code initialising a final variable:
public static final String EXTRA_MESSAGE="msg";
and then later in onCreate method:
tv.setText(getIntent().getStringExtra(EXTRA_MESSAGE));
The text displayed in the activity is not "msg" but is the string passed from the intent "I am the other activity". Why do you have to have the variable declaration above for the code to work? I don't understand what its doing.
Thanks
You are getting the extra received from another Activity indexed by the key 'msg'.
Like when you do this with the Intent used to start your Activity:
intent.putExtra("msg", "text going in the TextView");
The key is 'msg', but the value you get for the TextView is 'text going in the TextView'
Yes, final means EXTRA_MESSAGE value won't change, but you're not displaying EXTRA_MESSAGE value, but
getIntent().getStringExtra(EXTRA_MESSAGE)
which actually contains the value put in the previous activity. Regarding your question
Why do you have to have the variable declaration above for the code to work?
You don't actually need that variable for the code to work, but it's a good practice to use constant values instead of just hardcoding string values such in.-
getIntent().getStringExtra("msg")
The parameter you pass to getStringExtra is the key to which the String is mapped. All the extras you put in an Intent are mapped as key-value, so if you want to get a value you have to know the key, which must be the same key you used in the previous activity to save the value (with putStringExtra).
http://developer.android.com/reference/android/content/Intent.html#getStringExtra(java.lang.String)
I have question for receive value in smartwatch. Currently I follow this steps from this question
Actually,the person who ask it has the answer how to do that, but since my reputation for comment is not enough, so I can't ask question by comment in his/her question.
Right now, based on Mr. Eir,the person who answered the question. I have problem in what he answered:
You also want to pass some arguments to your Extension, i.e. the
String you mention. This can be a bit tricky; normally, you would pass
that String in the Intent itself, as an extra, but here, that is not
available. You need to save that information (the String) on a
location that your Extension can access as well. So, if your Activity
and your Extension are part of the same app, that location can be the
app preferences: the Activity saves the value in the preferences, and
the Extension reads it from the same preference and displays it on the
SmartWatch or whatever.
He said that I can save the value in preference and the Extension reads it from the same preference and displays it on the SmartWatch. Unfortunately, I don't know how the extension reads it. I have try to put the value in samplepreferenceactivity:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
SharedPreferences settings = getSharedPreferences("SHARED_PREFS_FILE",0);
String message = settings.getString("send", "message");
}
I don't know how to put the value in controlextension class, If it possible to put, I want to you use for changing "Hello watch". Below you can find controlextension class:
public class HelloWatchExtension extends ControlExtension{
...
public HelloWatchExtension(Context context, String hostAppPackageName) {
super(context, hostAppPackageName);
width = getSupportedControlWidth(context);
height = getSupportedControlHeight(context);
layout = new RelativeLayout(context);
textView = new TextView(context);
textView.setText("Hello watch!");
textView.setTextSize(9);
textView.setGravity(Gravity.CENTER);
textView.setTextColor(Color.WHITE);
textView.layout(0, 0, width, height);
layout.addView(textView);
}
Since it is not activity, so it is n't possible to take by using getpreference. Anybody knows how?
"Since it is not activity, so it is n't possible to take by using getpreference. Anybody knows how?"
You can access the preferences through context:
context.getApplicationContext().getSharedPreferences(...);
A few pointers about using shared preferences:
SharedPreferences preferences = _context. getApplicationContext().getSharedPreferences("com.example.AppName", Context. MODE_MULTI_PROCESS);
Putting string in shared preferences:
_preferences.edit().putString(“OBJECT”, “object_name”).commit();
Retreaving string from shared preferences:
_preferences.getString(“OBJECT”, "default_name");
If you are just trying to pass a string between an Activity in your project and your ControlExtension you don't need to use SharedPreferences. The easiest way is to just register a dynamic BroadcastReceiver in your extension and broadcast an Intent from the Activity passing your string inside the Intent.
I have an activity that has an EditText. After a user enters their text, the app may use that text later to make a notification. I can set the notification text just fine, but when the user clicks on the notification, it launches a dialog box that should have the same text. I have tried putExtra with the PendingIntent but that only displays the latest text in the dialog no matter which notification was selected. Is there a way to assign each string from the EditText a number and have the dialog load the text from what number it is?
try following logic,
make one static string variable,
private static strEditText = null;
at the time of EditText input, just store its value ion to strEditText variable like below,
strEditText = EditText.getText().toString().trim();
Now make one public static method, like below,
public static String EditTextValue()
{
return strEditText;
}
Now you can have this variable's value throughout whole project.
You can also try another method in android,
pass your arguments in Bundle
The PendingIntents are pooled/cached and the extra's don't make them different entries, so if you have a bunch of notifications with pendingIntents and the only difference between the intents are extras, then you'll end up with the notifications all using the one of the pendingIntents. [This sounds like what you're seeing, I remember this driving me nuts for a while]. You need to make your pending intents differ in something that the pool/cache cares about, like the data URI or action.
Im going a little crazy with this. In my app, i take a string which represents a bus stop, and then have an algorithm that matches it and displays its schedule. I needed to make that window an activity instead of a dialog and am using intents. Heres my code to send the intent:
Intent intent = new Intent(context, StopDialogActivity.class);
intent.putExtra("stop name", stopName);
context.startActivity(intent);
and heres my code to retrieve the string (in my onCreate):
Bundle extras = getIntent().getExtras();
departureStopName=extras.getString("stop name");
The string displays properly, but it isnt equal to a test string i have which is the same stop. The intent sends an integer over correct, what am i doing wrong with processing strings?
Make sure when comparing strings to use testName.equals(stopName) and not testName == stopName.
Using .equals() uses the equals method in the String class which compares the content. Using == compares the String Objects themselves, which need to be the same object in memory to evaluate to true.
Ah, my problem was while I use .equals() as a test to see if it was coming through okay, i was using == in the part of my code that broke.
In my app I have 5 String arrays that represent different fields of objects.
i.e.
String_A[1],
String_B[1],
String_C[1],
String_D[1],
String_E[1],
All are attributes of the same object (which is not really an object).
Now I want to store those in order to be able to use them in a new activity that I am creating. Since you are not able to pass objects around I thought that i should save them in Shared preferences.
My question is: Should I save them as separate strings or create a new class with all those fields and then serialize the objects?
Which is the best way in terms of memory usage? In fact is there any other way that you might achieve similar functionality?
Thanks in advance
Mike
If each of those String Arrays are big "enough" and it appears you do want to store them - have you considered Sqlite? SharedPreferences is most effective to store primitive data in key-value pairs. Check this link - it has neat comparison about the options you have - http://developer.android.com/guide/topics/data/data-storage.html
You can pass around objects via an intent. The extras function of an intent can store a bundle and send it to specified activities, however they cannot be called at any time (like from a later activity without being explicitly sent). If this is a one time pass to a different activity, the you'd probably want to use that.
http://developer.android.com/reference/android/content/Intent.html#putExtras%28android.content.Intent%29
Here is an example from a test app I made a while back:
public void onClick(View v) {
switch(v.getId()) { //this references the unique ID of the view that was clicked
case R.id.Button01: //this is what happens when the Button in the XML with android:id="#+id/Button01" is clicked
Intent nameGreet = new Intent(this, MainMenu.class);//creates Intent which will send the EditText input
String theName = firstName.getText().toString();// creates a new string named "theName" which is the text from an EditText called "firstName"
nameGreet.putExtra("helloName", theName);//puts the input from EditText into the Intent, this is a key/value pair
this.startActivity(nameGreet);//setting off the Intent
break;
Then you catch it like so:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setContentView(R.layout.main_menu);
String personsname = this.getIntent().getStringExtra("helloName");
welcome = (TextView)this.findViewById(R.id.TextView01);
welcome.setText(personsname);
Hope this helps.
You can pass a Serializable using an Intent.
Intent.putExtra(String name, Serializable value).