69 lines
3.1 KiB
Plaintext
69 lines
3.1 KiB
Plaintext
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page.title=Can I Use this Intent?
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@jd:body
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<p>Android offers a very powerful and yet easy-to-use message type called
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an <a href="{@docRoot}guide/topics/intents/intents-filters.html">intents</a>.
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You can use intents to turn applications into high-level libraries and
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make code modular and reusable. The Android Home screen and AnyCut
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applications, for instance, use intents extensively to create shortcuts. </p>
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<p>While it is nice to be able to make use of a loosely coupled
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API, there is no guarantee that the intent you send will be received by
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another application. This happens in particular with third-party apps, like
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<a href="http://code.google.com/p/apps-for-android/source/browse/trunk/Panoramio">Panoramio</a>
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and its RADAR intent.</p>
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<p>This article describes a technique you can use to find out whether the system
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contains any application capable of responding to the intent you want to use.
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The example below shows a helper method that queries the system package manager
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to determine whether there's an app that can respond to a specified intent. Your
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application can pass an intent to the method and then, for example, show or hide
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user options that the user would normally use to trigger the intent. </p>
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<pre class="prettyprint">/**
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* Indicates whether the specified action can be used as an intent. This
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* method queries the package manager for installed packages that can
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* respond to an intent with the specified action. If no suitable package is
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* found, this method returns false.
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*
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* @param context The application's environment.
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* @param action The Intent action to check for availability.
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*
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* @return True if an Intent with the specified action can be sent and
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* responded to, false otherwise.
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*/
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public static boolean isIntentAvailable(Context context, String action) {
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final PackageManager packageManager = context.getPackageManager();
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final Intent intent = new Intent(action);
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List<ResolveInfo> list =
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packageManager.queryIntentActivities(intent,
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PackageManager.MATCH_DEFAULT_ONLY);
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return list.size() > 0;
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}
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</pre>
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<p>Here is how you could use the helper method:</p>
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<pre class="prettyprint">@Override
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public boolean onPrepareOptionsMenu(Menu menu) {
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final boolean scanAvailable = isIntentAvailable(this,
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"com.google.zxing.client.android.SCAN");
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MenuItem item;
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item = menu.findItem(R.id.menu_item_add);
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item.setEnabled(scanAvailable);
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return super.onPrepareOptionsMenu(menu);
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}
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</pre>
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<p>In this example, the menu is grayed out if the <em>Barcode Scanner</em>
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application is not installed. </p>
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<p>Another, simpler, way to do this is to catch the
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<code>ActivityNotFoundException</code> when calling <code>startActivity()</code>
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but it only lets you react to the problem, you cannot predict it and update the
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UI accordingly to prevent the user from doing something that won't work. The
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technique described here can also be used at startup time to ask the user
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whether he'd like to install the missing package, you can then simply redirect
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him to the Android Market by using the appropriate URI.</p>
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