mobile programming lecture 4

Mobile ProgrammingLecture 4

Resources, Selection, Activities, Intents

Announcement

• Reminder: o Homework 2 is due this Friday 11:59pm. You need to

demo to me in class.o The second deadline is Sunday 11:59pm. You need to

demo to me in Monday’s class.o Please export your project (.zip) and email me.

• Midterm exam is on June 21st. It is a Friday.

Lecture 3 Review

• Why shouldn't you use Toast to debug?

• How should you debug?

Agenda

Referencing @string resources

• Setters and Getters

• Selection Views

• Android Components - Activity

• Intents

• More on the Android Manifest File

Referencing @string Resources

All @string Resources are stored in res/values/strings.xml

You reference them in XML as "@string/string_name"

Referencing @string ResourcesYou can also reference them in Java

String buttonText = "";Resources res = getResources();buttonText = res.getString(R.string.string_name);

Referencing ResourcesYou can store an array of strings if you need a collection

instead of just a single string. This makes it an @array resource instead of @string resource!

• Open res/values/strings.xml in Resources view

• Add ... > String Arrayo enter the name of the string_array, e.g. "countries"

• Repeat until you've added all values for the collection ...o Add ... > Itemo Enter the name of the item

Setters and Getters for Views

Most of a View's attributes can be set and get programmatically

Example widget XML attribute set method get method

EditText android:text setText(String) getText()

Button android:onClick setOnClickListener(OnClickListener) -

CheckBox android:checked setChecked(Boolean) isChecked()

SeekBar android:progress setProgress(int) getProgress()

SeekBar android:max setMax(int) getMax()

Selection Widgets - SpinnerSimilar to a drop-down list

• android:spinnerModeo "dialog" or "dropdown"

• android:prompto e.g. "Select an option"o message to display when the spinner dialog is shown

only when android:spinnerMode="dialog"

• android:entrieso e.g. "@array/countries"o populate the spinner using

this array





this array

If the list is static, you can again avoid Java by specifying the entries in XML!





this array

If you don't like XML, you can set the entries in Java also.

Selection Widgets - Spinnerpublic void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);setContentView(R.layout.main);

Spinner spinner = (Spinner) findViewById(R.id.my_spinner);

ArrayAdapter<CharSequence> adapter =ArrayAdapter.createFromResource(this, R.array.countries, android.R.layout.simple_spinner_item);

mySpinner.setAdapter(adapter); }






This is the Java code. If you choose to do this, then you don't need to set the android:entries attribute






You should already know what this does.






Since you don't like XML, to do it programmatically, you need to use an Adapter.






This is Java stuff. If you don't know what it is, try removing it to see what happens.






If you have an @array resource already, then create an ArrayAdapter from that resource.






First argument is of type Context, you can just past the "this" keyword here (because of the state of app)






This is the resource that you're creating the ArrayAdapter from.






3rd argument expects the @id of a TextView.






android.R gives you resources that exist for use even before you create your app






So instead of creating and using your own TextView for this purpose, use this one






Attach the Adapter to the Spinner in order to populate the Spinner!





adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);


Finally, this line of code is not required, but it makes your drop down look pretty.

Selection Widgets - Spinner

Both ways give you a Spinner which uses predetermined entries

How do you populate the Spinner at runtime, with when the entries are also determined at runtime?




String[] countries = new String[]{"Brazil","China","Denmark"};

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, countries);








Create and initialize a String array







Create an ArrayAdapter to populate the Spinner with







3rd argument accepts a List of Strings

Selection Widgets - ListView

A ListView is similar to a Spinner

• they both show the user a list of items

• they both have the android:entries attribute, so they can both be set using the same @array resource or the same ArrayAdapter

Selection Widgets - ListView Adapters are used to provide the data to the ListView

object.

The adapter also defines how each row is the ListView is displayed.

You can use pre-existing layout for each row.

You can also define customized layout for each row. Extends BaseAdapter class.

Selection Widgets - ListViewA ListView is similar to a Spinner with some exceptions, to name a few:

• A Spinner is normally used for forms, a ListView not so much

• A Spinner only shows one item at a time

• A Spinner item can be "selected", a ListView item can be "clicked" or "selected"

Selection Widgets - ListViewA ListView is similar to a Spinner with some exceptions,

to name a few:

• A Spinner is normally used for forms, a ListView not so much

• A Spinner only shows one item at a time

• A Spinner item can be "selected", a ListView item can be "clicked" or "selected"

I added this in hindsight. On non-trouch-screen devices it can be selected

Events - Spinner OnItemSelected

You can set an EventListener for when the user selects an item from the Spinner

Events - Spinner OnItemSelectedmySpinner.setOnItemSelectedListener(new OnItemSelectedListener() {

@Overridepublic void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

Toast.makeText(getApplicationContext(), ((TextView) view).getText() , Toast.LENGTH_SHORT).show();

}

@Overridepublic void onNothingSelected(AdapterView<?> parent) {

Toast.makeText(getApplicationContext(), "You didn't select anything" , Toast.LENGTH_SHORT).show();

}});




}



}});

Setter method for setting the EventListener




}



}});

Anonymous class




}



}});

When an item is selected ...,




}



}});

You can now reference the actual View (i.e., each entry in Spinner is a TextView)




}



}});

The position of the view in the Adapter




}



}});

The android:id attribute of the view




}



}});

Cast the generic View to a TextView




}



}});

Get the android:text value

Events - Spinner OnItemSelected• Note that this we're using the OnItemSelectedListener

instead of the OnItemClickListener for Spinner!• If you try to use OnItemClickListener you may get errors

• Also, note the difference between these two listeners and OnClickListenero OnItemClickListener

an entry in the Spinner has been clicked, don't use thiso OnClickListener

the Spinner has been clickedo OnItemSelectedListener

an entry in the Spinner has been selected

Events - ListView OnItemClick

As mentioned before, a ListView item can be clicked, or selected

In that case, you use OnItemClickListener for ListView or OnItemSelected Listener

Events - ListView OnItemClick

myListView.setOnItemClickListener(new OnItemClickListener() {@Overridepublic void onItemClick(AdapterView<?> parent, View view, int position, long id) {

Toast.makeText(getApplicationContext(), ((TextView) view).getText(), Toast.LENGTH_SHORT).show();

}});

Android Application Components

So far we've only been working with 1 of the 4 Android components, namely Activity

Android Application Components

The 4 Android application components are

1. Activity

2. Broadcast Receiver

3. Content Provider

4. Service

Activity

So far we've only been working with a single Activity

Remember, an Activity is a single screen with a user interface

Each Activity in an application is independent

Activity

An Activity is the only Android application component with a UI!

Activity

In Homework 2, you're creating a form that doesn't do anything after the form is submitted

If you want to take the user to a different screen after the form is submitted, you should add a new Activity to your app.

Activity

To add a new Activity• open the AndroidManifest.xml file

• click on the Application tab at the bottom of the window

• under the Application Nodes section, click Add ...

• select Activity

• in the Attributes for Activity section, click on the Name* link

• Enter the name of your second Activity

• Finish

http://www.google.com/

You can design the UI for your second Activity e.g. add another res/layout/xml_file.xml

Now we need to figure out how to launch the second Activity B from the first Activity A

Activity

Intent

An Intent is an abstract description of an operation to be performed

You can use it to launch another Activity B from within Activity A using an Intent

Activity A Activity BIntent

Activity and Intent

...

public void onClick(View view){

Intent myIntent = new Intent(A.this, B.class);startActivity(intent);

}

...

Activity and Intent

...



}

...

The name of the Activity the app is currently running

Activity and Intent

...



}

...

The name of the Activity that should be launched

Activity and Intent

...



}

...

Launch Activity B now

Activity - Android Manifest File

• If you added the second Activity B this way, then B will be automatically added to the Android Manifest file

• If you added it some other way, then Activity B may not be in the Manifest File. This is an easy to get a Force Close when you try to launch Activity B!

• Android needs to know what Activities your app may launch

Activity - ListActivity

Sometimes the entire UI for your Activity may be a ListView

In this case, you can extend ListActivity instead of extending Activity

You don't need a layout.xml file for a ListActivity!

Activity - ListActivitypublic class MyListActivity extends ListActivity {

@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);

setContentView(R.layout.main);String[] list = new String[]{"one","two","three"};

ArrayAdapter<CharSequence> adapter = new ArrayAdapter<CharSequence>(this,

android.R.layout.simple_list_item_1, list);

setListAdapter(adapter); }}



setContentView(R.layout.main);String[] list = new String[]{"one","two","three"};ArrayAdapter<CharSequence> adapter = new ArrayAdapter<CharSequence>(this,



extend ListActivity instead of Activity



setContentView(R.layout.main);String[] list = new String[]{"one","two","three"};ArrayAdapter<CharSequence> adapter = new ArrayAdapter<CharSequence>(this,



We don't need to setContentView because we're extending ListActivity



String[] list = new String[]{"one","two","three"};ArrayAdapter<CharSequence> adapter = new ArrayAdapter<CharSequence>(this,



We don't need to setContentView because we're extending ListActivity



String[] list = new String[]{"Brazil","China","Denmark"};ArrayAdapter<CharSequence> adapter = new ArrayAdapter<CharSequence>(this,



We've seen this before in this lecture






We've also seen this before in this lecture






We call setListAdapter on this ListActivity instead of calling it on a ListView (we don't have a ListView specified in an XML file this time!)






This is equivalent to calling this.setListAdapter(adapter);i.e., using the this keyword to refer to this instance of MyListActivity

References

• The Busy Coder's Guide to Android Development - Mark Murphy

• Android Developers

• The Mobile Lab at Florida State University

http://commonsware.com/

http://commonsware.com/

http://developer.android.com/

http://en.wikipedia.org/wiki/Event-driven_programming

mobile programming lecture 4

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