Develop Reference

Navigate Between Activities (Android Studio)

I got a problem when I navigate between two activities, it shows me error and I don't know what is the problem. I am very sure that my code is correct, because it just simple Intent navigate by on click Button.
When I Press the button to go to the next activity it returns me to the fist activity (not the desire one). Note that both activity has background image.
Fist Activity
public class firstActivity extends AppCompatActivity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.first_activity);//has a background img and one button
}
public void nextPage(View view){
Intent StartNewActivity = new Intent(firstActivity.this, secondActivity.class);
startActivity(StartNewActivity);
overridePendingTransition(R.layout.slide_in_up, R.layout.slide_out_up);
}
}
Second Activity
public class secondActivity extends AppCompatActivity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.second_activity);// has a background img and one button
}
public void nextPage(View view){
Intent StartNewActivity = new Intent(secondActivity.this, thirdActivity.class);
startActivity(StartNewActivity);
overridePendingTransition(R.layout.slide_in_up, R.layout.slide_out_up);
}
}
This is the error message
Could not find class 'android.graphics.drawable.RippleDrawable', referenced from method android.support.v7.widget.AppCompatImageHelper.hasOverlappingRendering
Also, I did not use any ripple drawable in my app.Even though I don't know what does it mean?
Thanks,

Something you have wants to to find a refwrence to that ripple component, you need to find out what.
Otherwise, you can try to make sure you have added a reference to the support.v7.widget in the second activity and see if the exception goes away.
Aside from that, we would need to see more code to help further.

When I Press the button to go to the next activity it returns me to the fist activity (not the desire one)
It means that your app crashes when loading your new activity, so it comes back the first one.
Check your activity layout, style configuration => clean your project => Run again.
Hope it can help.

I solved my problem by resizing the background images of the activities, and I added this extra attribute in the manifests file
<application
android:largeHeap="true" >
</application>

When good time to start another activity

I have an Android Best Practice question. I have to following code, which is working nicely, but I think it is not so elegant. So, my question is: at which point of activity life cycle is nice to start another activity ?
public class LoginActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ParentPreferences parentPreferences = new ParentPreferences(getApplicationContext());
if (parentPreferences.isPassExists()) {
Intent i = new Intent(this, MainActivity.class);
startActivity(i);
} else {
setContentView(R.layout.login);
}
}
}
The task is about: if the parent has already made a password to protect the app, than we don't need to show the LoginActivity. I don't know, is it "healthy" for an Activity to give an intent to launch, when nor the onCreate nor the other lifecycle methods completed.
What are you thoughts guys ?

I think the better way is to create LauncherActivity, and start activitys from them:
For example:
public class LauncherActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ParentPreferences parentPreferences = new ParentPreferences(getApplicationContext());
Intent intent;
if (parentPreferences.isPassExists()) {
intent = new Intent(this, MainActivity.class);
} else {
intent = new Intent(this, LoginActivity.class);
}
intent.addFlags(Intent.FLAG_ACTIVITY_NO_HISTORY)
startActivity(i);
}
}
Updated:
Refering to Activity | Android Developer
onCreate is a first lifecycle method, сonsequently better to start activity B when A activity just started and does not inflate any layout

I would have the manifest start your MainActivity or whatever you call it. The MainActivity starts by checking if the user has logged in. If not, it starts your LoginActivity, which comes back in onActivityResult() with the result of the login.
It does depend on the requirement for the user to log in every time they start the app, or just once, or once in a while. If the use has to log in every time, than it's ok to start with LoginActivity. Otherwise, starting LoginActivity every time and passing to MainActivity (or whatever) seems just a waste. "Waste" not in the sense of performance, but of clarity of your app.

I think the best solution for you is to add a SplashScreen or like a "fake" screen.
Here you check if he's logged in already and based on it you start the correct activity.
Maybe the absolutely best way would be to do it with fragments, but you have to change a lot of your app.
About when to call it, the onCreate is perfect :)

Pass reference of one Activity to another Activity

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.

How to go back from second screen to first screen

How to switch layouts? First, I have a class Main where is onCreate (setContentView(R.layout.main);) and then I call, another class with command:
setContentView(secondClass);
In this class, I draw with Canvas and this work just fine. I also create button to go back in first "class" (R.layout.main), but I don't know how to do it.
Now my program is basic a graph shower. In first class you type your function and them second class draw it. But how to go back in first class to type another function. This "back" button or arrow witch every Android phone have, send me out of program not back on insert part.
In secondClass I can't create onCreate method, but I also tried the following and they didn't work:
Intent abc = new Intent("bla.bla.bla.FIRSTCLASS");
startActivity(abc);
and
Intent abc = new Intent(SecondClass.this,FirstClass.class);
startActivity(greNaPrvoOkno);

If you want to use a custom view (as I understood, you are extending the View class), you can do it in the following way;
Consider you are showing the second class from your Main activity like this;
setContentView(new SecondClass(getApplicationContext(), MainActivity.this));
And you Second class is this (suppose);
// I am using onClickListener to go back to main view. You do whatever you like.
public class SecondClass extends View implements OnClickListener {
// This is needed to switch back to the parent activity
private Activity mParentActivity = null;
public SecondClass(Context context, Activity parentActivity) {
super(context);
mParentActivity = parentActivity;
setOnClickListener(this);
}
#Override
public void onClick(View v) {
// Set the Main view back here.
mParentActivity.setContentView(R.layout.main);
}
}
Disclaimer: This code will do what you have asked for, but may cause other problems.
As advised by #Mudassir, you should use two different activities for two screens. It will give you better control, and your code will be easy to understand and maintain.

On the Onclick event of the button you have to write finish(); that's it..

Both of your classes are Activities yes? IF so then in your second activity you will simply call finish() and your activity will close revealing your first activity again.

When I have used multiple intents in my android application, I have created a new activity through:
Intent abc = new Intent(this, SecondClass.class);
startActivity(abc);
When the button is pressed in your second class, I would then either call finish(); on the class, or create a new intent like so:
Intent abc = new Intent(this, FirstClass.class);
startActivity(abc);
However, this method has the disadvantage that if a user wanted to use the back button, they may have to scroll through many layers of activities.

You should create another activity for your second class but not just set the main activity to a new view setContentView(secondClass).
For an easier modification, You could try to set the view back to setContentView(R.layout.main) first.
You still need to configure the widgets(e.g. TextView) on it when you set it back.
You don't have to startActivity again to go back.
Just call finish() in your second activity when you want to finish the current activity and go back:
e.g. When user press the back button in your second activity
mButtonBack.setOnClickListener(new Button.OnClickListener()
{
public void onClick(View v)
{
finish();
}
}

Android (student cw) in need of direction

public class Menu extends Activity {
/** Called when the activity is first created. */
public void onCreate(Bundle icicle) {
//myIntent.setClassName("hello.World", "hello.World.mybuttonclick");
// myIntent.putExtra("com.android.samples.SpecialValue", "Hello, Joe!"); // key/value pair, where key needs current package prefix.
//startActivity(myIntent);
//Button myButton = (Button) findViewById(R.id.my_button);
super.onCreate(icicle);
setContentView(R.layout.main);
}
public void updateLayout(){
Intent myIntent = new Intent(Menu.this, mybuttonclick.class);
startActivity(myIntent);
// TextView sayHello = (TextView) findViewById(R.id.Hello);
}
}
Hey guys, I am a new android java student and we have to develop a simple hello world app.. I am finding some difficulty getting my onClick() activity to work, using android:Onclick in xml.. what i am trying to do is change the content view do display a simply a different layout and saying hello.. i am using setContentLayout to do this, every time i click said button tho the android app crashes out.. am i doing something wrong?
regards,
Stefan

When you set a click listener in xml you must have the method defined inside the activity you are clicking in. Lets say you set the onClick in xml to be "buttonClicked", you must create a method looking exactly like the one below.
public void buttonClicked(View view)
{
//Your code here
}
The thing to notice is that the method is a public void with only a single parameter of type View. XML defined click listeners must be like this to work. The view object in the example above is the view that was clicked.

You update layout function needs to read
public void updateLayout(View view)

In response to your question, there are a number of things that are issues causing the complication that you described. Let it first be said, that you don't have to do anything any particular way, provided that you make concessions for certain things. Android is a very flexible platform and Java, as an OOP language allows you to do things that many non OOP languages do not.
Whenever you create a "clickable" item, like a Button, if you want to have your program respond, you must have something "listen" to it. This is known as a Listener. In your case, you are looking for an OnClickListener. The OnClickListener does not have to be a part of the Activity necessarily. It just has to be a class that implements View.OnClickListener. Then, you have tell the setOnClickListener() method of the Button who its listener is. The following example shows what is necessary without your declaration in XML (but it is important).
class Menu extends Activity implements View.OnClickListener
{
public void onCreate(Bundle icicle)
{ setContentView(R.layout.main);
Button btn = (Button)findViewById(R.id.BUTTON_ID_AS_DEFINED_BY_YOUR_XML);
btn.setOnClickListener(this);
}
public void onClick(View view)
{ int id = view.getId();
if (id == R.id.BUTTON_ID_AS_DEFINED_BY_YOUR_XML)
updateLayout()//Do your Click event here
}
public void updateLayout()
{ //updateLayout code...
}
}
Something that needs to be noted is the OnClick() above. Every OnClickListener must use the same signature as theOnClick() That means itmust have the same return and same arguments even if it has a different name. For what you are trying to do (in XML), you have set your android:OnClick to updateLayout. This means that `updateLayout() must be declared as follows:
public void updateLayout(View view)
Now, getting the update method to actually work: While you provide your code, we don't actually know what errors you are getting. It is always much easier to solve a problem if we have a copy of the Logcat output that includes the error you are receiving. Once, we have that we can target your error specifically and I can edit my answer to include what you may additionally need.
FuzzicalLogic