4.5.7. Anonymous Inner Class That Implements the ListView’s OnItemClickListener to Display Search Results
Figure 4.24 declares and initializes instance variable itemClickListener, which refers to an anonymous inner-class object that implements interface OnItemClickListener. Line 67 (Fig. 4.20) registered itemClickListener as the ListView’s event handler that responds when the user touches an item in the ListView. Lines 131–145 override interface OnItemClickListener’s onItemClick method. The method’s arguments are:
• The AdapterView where the user touched an item. The ? in AdapterView<?> is a wildcard in Java generics indicating method onItemClick can receive an AdapterView that displays any type of data—in this case, a ListView<String>.
• The View that the user touched in the AdapterView—in this case, the TextView that displays a search tag.
• The zero-based index number of the item the user touched.
• The row ID of the item that was touched—this is used primarily for data obtained from a database (as you’ll do in Chapter 8).
128 // itemClickListener launches web browser to display search results
129 OnItemClickListener itemClickListener = new OnItemClickListener()
130 {
131 @Override
132 public void onItemClick(AdapterView<?> parent, View view,
133 int position, long id)
134 {
135 // get query string and create a URL representing the search
136 String tag = ((TextView) view).getText().toString();
137 String urlString = getString(R.string.searchURL) +
138 Uri.encode(savedSearches.getString(tag, ""), "UTF-8");
139
140 // create an Intent to launch a web browser
141 Intent webIntent = new Intent(Intent.ACTION_VIEW,
142 Uri.parse(urlString));
143
144 startActivity(webIntent); // launches web browser to view results
145 }
146 }; // end itemClickListener declaration
147
Fig. 4.24 | Anonymous inner class that implements the ListView’s OnItemClickListener to display search results.
Getting String Resources
Line 136 gets the text of the View that the user touched in the ListView. Lines 137–138 create a String containing the Twitter search URL and the query to perform. First, line 137 calls Activity’s inherited method getString with one argument to get the String resource named searchURL, which contains the Twitter search page’s URL:
As with all the String resources in this app, you should add this resource to strings.xml.
Getting Strings from a SharedPreferences Object
We append the result of line 138 to the search URL to complete the urlString. SharedPreferences method getString returns the query associated with the tag. If the tag does not already exist, the second argument ("" in this case) is returned. Line 138 passes the query to Uri method encode, which escapes any special URL characters (such as ?, /, :, etc.) and returns a so-called URL-encoded String. This is important to ensure that the Twitter web server that receives the request can parse the URL properly to obtain the search query.
Creating an Intent to Launch the Device’s Web Browser
Lines 141–142 create a new Intent, which we’ll use to launch the device’s web browser and display the search results. Intents can be used to launch other activities in the same app or in other apps. The first argument of Intent’s constructor is a constant describing the action to perform. Intent.ACTION_VIEW indicates that we’d like to display a representation of the data. Many constants are defined in the Intent class describing actions such as searching, choosing, sending and playing. The second argument (line 142) is a Uri (uniform resource identifier) representing the data on which we want to perform the action. Class Uri’s parse method converts a String representing a URL (uniform resource locator) to a Uri.
Starting an Activity for an Intent
Line 144 passes the Intent to the inherited Activity method startActivity, which starts an Activity that can perform the specified action on the given data. In this case, because we’ve specified to view a URI, the Intent launches the device’s web browser to display the corresponding web page. This page shows the results of the supplied Twitter search.