Mobile Programming Lecture 3 - ww2.cs.fsu.eduww2.cs.fsu.edu/~yannes/lectures/lect03.Resources.Selection.Activiti… · Lecture 3 Resources, Selection, Activities, Intents . ... Referencing

Mobile ProgrammingLecture 3

Resources, Selection, Activities, Intents

Lecture 2 Review

● What widget would you use to allow the user to enter○ a yes/no value○ a range of values from 1 to 100

● What's the benefit of a TableLayout over LinearLayout?

● How many ways can you set an event listener?

Lecture 2 Review

● How do you make the android:inputType attribute of an EditText both textCapWords and textMultiLine?

● Why should you use a @string resource for TextViews instead of hardcoding the string?

● If you use the same android:onClick value for multiple views, how do you determine which one was clicked?

AgendaReferencing @string resources● Setters and Getters● Selection Views● Android Components - Activity● Intents● More on the Android Manifest File

String Resources

● Three types of string resources○ String○ String Array○ Quantity Strings

String Resources


String Resources - String

Used to store a single string resource

<string name=”sample_string”>Sample String</string>

Referenced using ● @string/<string> - in XML● Resources res = getResources();

res.getString() / getText()//getText() retains any text styling

String Resources


String Resources - String Array

Used to provide an array of strings

<string-array name=”array_name”>

<item>Item 1</item>

<item>Item 2</item>

<item>Item 3</item>

</string-array>

Referenced using:● @array/array_name in XML● Resources res = getResources();

res.getStringArray();

String Resources


String Resources - Quantity Strings

Used to provide different string outputs for plurals

<plurals name=”plural_name”>

<item quantity=”one”>%d student has an A</item>

<item quantity=”other”>%d students have an A</item>

</plurals>

Referenced using:● Resource res = getResources();

res.getQuantityString(R.plurals.plural_name,

count, count);

Referencing @string Resources

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

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

Referencing @string Resources

You can also reference them in Java

String buttonText = "";

Resources res = getResources();

buttonText = res.getString(R.string.string_name);

Referencing Resources

You 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 and create the new

entry● You can also get some assistance by

○ Right-click the body of the strings.xml file○ Select Generate… > XML Tag…○ Select the appropriate resource type (string-array)

● Provide your resource with a name, e.g. "countries"● Add an <item> entry for each item in the array

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:onClicksetOnClickListener(OnClickListener)

-

CheckBox android:checked setChecked(Boolean) isChecked()

SeekBar android:progress setProgress(int) getProgress()

SeekBar android:max setMax(int) getMax()

Selection Widgets - Spinner

Similar to a drop-down list● android:spinnerMode

○ "dialog" or "dropdown"● android:prompt

○ e.g. "Select an option"○ message to display when the spinner dialog is shown

■ only when android:spinnerMode="dialog"● android:entries

○ e.g. "@array/countries"○ populate the spinner using this array


Similar to a drop-down list● android:prompt


● android:spinnerMode○ "dialog" or "dropdown"

● android:entries○ e.g. "@array/countries"○ populate the spinner using this array

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


Similar to a drop-down list● android:prompt


● android:spinnerMode○ "dialog" or "dropdown"

● android:entries○ e.g. "@array/countries"○ populate the spinner using 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 mySpinner = (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.




Spinner spinner = (Spinner)





}

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 pass 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!




Spinner mySpinner = (Spinner) findViewById(R.id.my_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.


● Both ways give you a Spinner which uses predetermined entries

● How do you populate the Spinner at runtime, 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);


}




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

String[] countries = new String[] { "Brazil", "China",

"Denmark" };




}

Create and initialize a String array






"Denmark"};




}

Create an ArrayAdapter to populate the Spinner with






"Denmark" };




}

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


A 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"


A 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"

This was added in hindsight. On non-touch-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() {

@Override

public void onItemSelected(AdapterView<?> parent, View view,

int position, long id) {

Toast.makeText(getApplicationContext(),

((TextView) view).getText() ,

Toast.LENGTH_SHORT).show();

}

@Override

public void onNothingSelected(AdapterView<?> parent) {


"You didn't select anything",


}

});


@Override






}

@Override



"You didn't select anything" ,


}

});

Setter method for setting the EventListener


@Override






}

@Override





}

});

Anonymous class


@Override






}

@Override





}

});

When an item is selected ...,


@Override






}

@Override





}

});

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


@Override






}

@Override





}

});

The position of the view in the Adapter


@Override






}

@Override





}

});

The android:id attribute of the view


@Override






}

@Override





}

});

Cast the generic View to a TextView


@Override






}

@Override





}

});

Get the android:text value

Events - Spinner OnItemSelected

● Note that we're using OnItemSelectedListener instead of OnItemClickListener for Spinner!

● If you try to use OnItemClickListener you may get errors

● Also, note the difference between these two listeners and OnClickListener

○ OnItemClickListener■ an entry in the Spinner has been clicked, don't use this

○ OnClickListener■ the Spinner has been clicked

○ 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 or OnItemSelectedListener

Events - ListView OnItemClickmyListView.setOnItemClickListener(new OnItemClickListener() {

@Override

public void onItemClick(AdapterView<?> parent, View view,



((TextView) view).getText(),


}

});

Android Application Components

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


The 4 Android application components are 1. Activity

2. Broadcast Receiver

3. Content Provider

4. Service


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 simply displays the data after the form is submitted

● In order 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● Right-click your project and choose New > Activity● Select an Activity template, provide a name for the Layout

Resource file and provide any other necessary information● Click FinishOr … ● Create a new Java class that extends the Activity base

class● Open the AndroidManifest.xml file● Add a new <activity> tag and configure the appropriate

attributes● Save the AndroidManifest.xml file

● You can design the UI for your second Activity as well○ 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 an Intent to launch another Activity B from within Activity A

Activity and Intent

...

public void onClick(View view)

{

Intent myIntent = new Intent(A.this,

B.class);

startActivity(intent);

}

...

Activity and Intent

...


{

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

startActivity(myIntent);

}

...

The name of the Activity the app is currently running

Activity and Intent

...


{


B.class);startActivity(myIntent);

}

...

The name of the Activity that should be launched

Activity and Intent

...


{


B.class);

startActivity(myIntent);}

...

Launch Activity B now

Activity - Android Manifest File

● If you added the second Activity B using the wizard/template, then B will be automatically added to the Android Manifest file

● If you added it manually, 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

Passing Data between Activities

When you start Activity B from Activity A, you may want to send data to Activity B

Activity A Activity B

startActivity B

send some data to B also

Passing Data between Activities

Activity A - onCreate()

Intent intent = new Intent(this,

SecondActivity.class);

Bundle bundle = new Bundle();

bundle.putString( "fname", "John");

bundle.putString( "lname", "Doe");

bundle.putInt("age", 18);

intent.putExtras(bundle);

startActivity(intent);

Activity B - onCreate()

Intent intent = getIntent();

Bundle bundle = intent.getExtras();

if (bundle != null) {

edit1.setText(bundle.getString(

"fname"));

edit2.setText(bundle.getString(

"lname"));

int age= bundle.getInt( "age");

}

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 {

@Override

public void onCreate(Bundle savedInstanceState) {



String[] list = new String[] { "one", "two",

"three" };


new ArrayAdapter<CharSequence>(this,

android.R.layout.simple_list_item_1, list);

setListAdapter(adapter);

}

}


@Override




String[] list = new String[]{"one","two","three"};





}

}

extend ListActivity instead of Activity


@Override




String[] list = new String[]{"one","two","three"};





}

}

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


@Override



String[] list = new String[] { "Brazil", "China",

"Denmark"};





}

}

We've seen this before in this lecture


@Override



String[] list = new String[]{ "Brazil", "China",

"Denmark"};





}

}

We've also seen this before in this lecture


@Override




"Denmark"};





}

}

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!)


@Override




"Denmark"};





}

}

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://developer.android.com

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

Documents

Mobile Programming Lecture 3 - ww2.cs.fsu.eduww2.cs.fsu.edu/~yannes/lectures/lect03.Resources.Selection.Activiti… · Lecture 3 Resources, Selection, Activities, Intents . ... Referencing