Moving the Earthquake Service to a Background Thread

The following example shows how to move the network lookup and XML processing done in the

EarthquakeService onto a background thread:

Rename the refreshEarthquakes method to doRefreshEarthquakes.

private void doRefreshEarthquakes() {

[ ... previous refreshEarthquakes method ... ]

}

Create a new refreshEarthquakes method. It should start a background thread that executes the newly named doRefreshEarthquakes method.

private void refreshEarthquakes() {

Thread updateThread = new Thread(null, backgroundRefresh, “refresh_earthquake”);

updateThread.start();

}

private Runnable backgroundRefresh = new Runnable() { public void run() {

doRefreshEarthquakes();

}

};

Let’s Make a Toast

Toasts are transient Dialog boxes that remain visible for only a few seconds before fading out. Toasts don’t steal focus and are non-modal, so they don’t interrupt the active application.

Toasts are perfect for informing your users of events without forcing them to open an Activity or read a Notification. They provide an ideal mechanism for alerting users to events occurring in background Services without interrupting foreground applications.

The Toast class includes a static makeText method that creates a standard Toast display window. Pass the application Context, the text message to display, and the length of time to display it (LENGTH_SHORT or LENGTH_LONG) in to the makeText method to construct a new Toast. Once a Toast has been created, display it by calling show, as shown in the following snippet:

Context context = getApplicationContext();

String msg = “To health and happiness!”;

int duration = Toast.LENGTH_SHORT;

Toast toast = Toast.makeText(context, msg, duration); toast.show();

Figure 8-1 shows a Toast. It will remain on screen for around 2 seconds before fading out. The applica-tion behind it remains fully responsive and interactive while the Toast is visible.

Customizing Toasts

The standard Toast text message window is often sufficient, but in many situations you’ll want to cus-tomize its appearance and screen position. You can modify a Toast by setting its display position and assigning it alternative Views or layouts.

The following snippet shows how to align a Toast to the bottom of the screen using the setGravity method:

Context context = getApplicationContext();

String msg = “To the bride an groom!”;

int duration = Toast.LENGTH_SHORT;

Toast toast = Toast.makeText(context, msg, duration);

int offsetX = 0;

int offsetY = 0;

toast.setGravity(Gravity.BOTTOM, offsetX, offsetY); toast.show();

When a text message just isn’t going to get the job done, you can specify a custom View or layout to use a more complex, or more visual, display. Using setView on a Toast object, you can specify any View (including layouts) to display using the transient message window mechanism.

For example, the following snippet assigns a layout, containing the CompassView widget from Chapter 4 along with a TextView, to be displayed as a Toast.

Context context = getApplicationContext();

String msg = “Cheers!”;

int duration = Toast.LENGTH_LONG;

Toast toast = Toast.makeText(context, msg, duration); toast.setGravity(Gravity.TOP, 0, 0);

LinearLayout ll = new LinearLayout(context);

ll.setOrientation(LinearLayout.VERTICAL);

TextView myTextView = new TextView(context);

CompassView cv = new CompassView(context);

myTextView.setText(msg);

int lHeight = LinearLayout.LayoutParams.FILL_PARENT; int lWidth = LinearLayout.LayoutParams.WRAP_CONTENT;

ll.addView(cv, new LinearLayout.LayoutParams(lHeight, lWidth)); ll.addView(myTextView, new LinearLayout.LayoutParams(lHeight, lWidth));

ll.setPadding(40, 50, 0, 50);

toast.setView(ll);

toast.show();

Using Toasts in Worker Threads

As GUI components, Toasts must be opened on the GUI thread or risk throwing a cross thread excep-tion. In the following example, a Handler is used to ensure that the Toast is opened on the GUI thread:

private void mainProcessing() {

Thread thread = new Thread(null, doBackgroundThreadProcessing, “Background”); thread.start();

}

private Runnable doBackgroundThreadProcessing = new Runnable() { public void run() {

backgroundThreadProcessing();

}

};

private void backgroundThreadProcessing() {

handler.post(doUpdateGUI);

}

Runnable that executes the update GUI method.

 private Runnable doUpdateGUI = new Runnable() {

public void run() {

Context context = getApplicationContext(); String msg = “To open mobile development!”; int duration = Toast.LENGTH_SHORT; Toast.makeText(context, msg, duration).show();

}

};