View visibility

How do I hide and show view controls in my app?
View controls (TextView, EditText, Button, Image, etc) all have a visibility property. This can be set to one of three values:

• Visible - Displayed
• Invisible - Hidden but space reserved
• Gone - Hidden completely

The visibility can be defined in the layout XML:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <Button
     android:id="@+id/button1"
     android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_weight="1"
    android:text="You can see me"
    android:visibility="visible" />
    <Button
     android:id="@+id/button2" android:dr
     android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_weight="1"
    android:text="You cannot see me, but you can see where I am"
    android:visibility="invisible" />
    <Button
     android:id="@+id/button3"
     android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_weight="1"
    android:text="You have no idea that I am here"
    android:visibility="gone" />
</LinearLayout>

For the LinearLayout above, the three buttons laid out horizontally with equal weights will be displayed as below. You can see the first, the space for the second, but not the third:

To set the visibility in code use the public constant available in the static View class:

Button button1 = (TextView)findViewById(R.id.button1);
button1.setVisibility(View.Visible);

You see?

Quick Tip: Copyright symbol in a string

Very quick tip; to display the copyright symbol in your app, you can use Unicode definition in a string, as shown below:

<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="\u00A9 Android Elements 2011" />

Displaying the copyright notice in an app

Opening call dialog

How do I make my app call a phone number?
The easiest method is to create an intent which opens the device caller dialog. Because this is not actually initiating the call, no additional permissions are required by your app.

final String phoneNumber = "01234 123456";
startActivity(new Intent(Intent.ACTION_DIAL, Uri.parse("tel:" + phoneNumber)));

Android dialler intent

How to close soft keyboard on button press

How can my app hide the soft keyboard when a button is pressed?
A simple example of this requirement would be a search box within your app. This would be defined in your layout markup as a EditText view and a Button view. Once the user has entered some text, they will typically click on the search button. Default behaviour is that the soft keyboard is still visible until the user dismisses it. You can hide the keyboard using the following code, probably on the button click handler:

InputMethodManager inputMgr = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
EditText editText = (EditText)findViewById(R.id.editText);
inputMgr.hideSoftInputFromWindow(editText.getWindowToken(), 0);

The method requires a reference to the EditText view that was the source of the soft keyboard launch.

First Steps: Returning values from an Activity

How do I return  a value from an Activity?

Below is some simple example code for creating a new Intent to launch an Activity named Activity1. Here we use the startActivityForResult method which takes the intent and an identifier (an arbitrary integer):

Activity1.java:

final static int REQUEST_CODE = 1234;

private void startActivity() {
  Intent myIntent = new Intent(getBaseContext(), Activity2.class);
  myIntent.setAction(Intent.ACTION_VIEW);
  startActivityForResult(myIntent, REQUEST_CODE);
}

In your second activity you should use the following code to return a result value and terminate the activity:

Activity2.java:

...
  setResult(1);
  finish();
...

Returning to your first activity and override the activity's onActivityResult method as below. Check the result code to determine the result is coming from the expected source then you can read resultCode and change logic depending upon its value:

Activity1.java:

...
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
  super.onActivityResult(requestCode, resultCode, data);
  if(requestCode == REQUEST_CODE) {
    // Do something with resultCode
  }
}
...

It is worth noting that you can not open activities (or dialogs for that matter) in a modal fashion, in fact nothing is modal in android as that would lock the UI which is not permitted. Listeners are always used to receive the results.

First Steps - Passing values to an Activity

How do I pass a value to an activity?

To start an Activity you use an Intent. In this intent you can pass data which is returned as a Bundle object.

Android Activities and Intents

Below is some simple example code for creating a new intent to launch an Activity named MyActivity. Note the call to the putExtra method which accepts a key name ("content") and a value:

Intent myIntent = new Intent();
String packageName = this.getPackageName();
myIntent.setClassName(packageName,
packageName + "." + MyActivity.class.getSimpleName());
myIntent.putExtra("content", "my content string");
startActivity(myIntent);

Here is the code for the called activity with the Bundle data extracted from the intent. You can then retrieve the passed extra content from the bundle object:

public class MyActivity extends Activity {

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.contentweb);

    Bundle bundle = getIntent().getExtras();
    String content = bundle.getString("content");
  }
}

All pretty simple when you know how.

Android Development Tools ADT and DDMS Version 11 Release

Last week Google released a new version of the Android Development Tools (ADT). If you've not updated to version 11 yet, then DO IT NOW! There are a number of big improvements that will enhance your app development process, particularly regarding layouts and XML editing. Take a look at the video below for details of the update made at Google I/O 2011, if you've been developing on Android for a while, this should really get your juices flowing!



If you're not already then you should be following the Android Developers Blog (or @AndroidDev on Twitter).

How do update my tools in Eclipse?
Make sure you are running Eclipse as Administrator, then go to Help > Check for Updates.
Now just step through the sequence, agree to license terms then restart Eclipse when prompted.