Lập trình Androi part 53 ppsx

CHAPTER 36: Handling Multiple Screen Sizes 346 Figure 36–44. EU4You, original version, QVGA Fixing the Fonts The first problem that should be fixed is the font size. As you can see, with a fixed 20- pixel size, the font ranges from big to tiny, depending on screen size and density. For a WVGA screen, the font may be rather difficult to read. We could put the dimension as a resource (res/values/dimens.xml) and have different versions of that resource based on screen size or density. However, it is simpler to just specify a density-independent size, such as 5mm, as seen in the ScreenSizes/EU4You_2 project: <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="wrap_content" android:padding="2dip" android:minHeight="?android:attr/listPreferredItemHeight" > <ImageView android:id="@+id/flag" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center_vertical|left" android:paddingRight="4px" /> <TextView android:id="@+id/name" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center_vertical|right" android:textSize="5mm" /> </LinearLayout> CHAPTER 36: Handling Multiple Screen Sizes 347 Figures 36–5, 36–6, and 36–7 shows the results on HVGA, WVGA, and QVGA screens. Figure 36–5. EU4You, 5mm font version, HVGA Figure 36–6. EU4You, 5mm font version, WVGA (800x480 pixels) CHAPTER 36: Handling Multiple Screen Sizes 348 Figure 36–7. EU4You, 5mm font version, QVGA Now our font is a consistent size and large enough to match the flags. Fixing the Icons So, what about those icons? They should be varying in size as well, since they are the same for all three emulators. However, Android automatically scales bitmap resources, even with <supports-screens> and its attributes set to true. On the plus side, this means you may not need to do anything with these bitmaps. However, you are relying on a device to do the scaling, which definitely costs CPU time (and, hence, battery life). Also, the scaling algorithms that the device uses may not be optimal, compared to what you can do with graphics tools on your development machine. The ScreenSizes/EU4You_3 project creates res/drawable-ldpi and res/drawable-hdpi, putting in smaller and larger renditions of the flags, respectively. This project also renames res/drawable to res/drawable-mdpi. Android will use the flags for the appropriate screen density, depending on what the device or emulator needs. Using the Space While the activity looks fine on WVGA in portrait mode, it really wastes a lot of space in landscape mode, as shown in Figure 36–8. CHAPTER 36: Handling Multiple Screen Sizes 349 Figure 36–8. EU4You, landscape WVGA (800x480 pixels) We can put that to better use by having the Wikipedia content appear directly on the main activity when in large-screen landscape mode, instead of needing to spawn a separate browser activity. To do this, we first must clone the main.xml layout into a res/layout-large-land rendition that incorporates a WebView widget, as seen in ScreenSizes/EU4You_4: <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" > <ListView android:id="@android:id/list" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1" /> <WebView android:id="@+id/browser" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1" /> </LinearLayout> Then we need to adjust our activity to look for that WebView and use it when found; otherwise, it will default to launching a browser activity: @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); browser=(WebView)findViewById(R.id.browser); setListAdapter(new CountryAdapter()); } @Override CHAPTER 36: Handling Multiple Screen Sizes 350 protected void onListItemClick(ListView l, View v, int position, long id) { String url=getString(EU.get(position).url); if (browser==null) { startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse(url))); } else { browser.loadUrl(url); } } This gives us a more space-efficient edition of the activity, as shown in Figure 36–9. Figure 36–9. EU4You, landscape WVGA (800x480 pixels), set for normal density, and showing the embedded WebView When the user clicks a link in the Wikipedia page, a full browser opens, for easier surfing. Note that to test this version of the activity, and see this behavior, requires a bit of extra emulator work. By default, Android sets up WVGA devices as being high-density, meaning WVGA is not large in terms of resource sets, but rather normal. You will need to create a different emulator AVD that is set for normal (medium) density, which will result in a large screen size. What If It’s Not a Browser? Of course, EU4You does cheat a bit. The second activity is a browser (or WebView in the embedded form), not some activity of your own creation. Things get slightly more complicated if the second activity is some activity of yours, with many widgets in a CHAPTER 36: Handling Multiple Screen Sizes 351 layout, and you want to use it both as an activity (for smaller screens) and have it embedded in your main activity UI (for larger screens). Here is one pattern to deal with this scenario: 1. Initially develop and test the second activity as an activity. 2. Have all of the second activity’s life-cycle methods delegate their logic to an inner class. Move all data members of the activity that are needed by only the inner class to that inner class, and ensure that still works. 3. Pull the inner class out into a separate public class, and ensure that still works. 4. For your first (or main) activity, create a separate layout for large screens and use the <include> directive to blend in the contents of your second activity’s layout into the proper spot in the large-screen first activity’s layout. 5. In the first activity, if it finds the second activity’s layout has been inflated as part of its own (e.g., by checking for the existence of some widget via findViewById()), create an instance of the public class you created in step 3 and have it deal with all of those widgets. Adjust your code to reference that class directly, rather than start the second activity as shown in the previous section. In short, use a public class and reusable layout to keep your code and resources in one place, yet use them from both a stand-alone activity and as part of a large-screen version of the main activity. What Are a Few Bugs Among Friends? The Motorola DROID, which shipped with Android 2.0, had two bugs of relevance for screen sizes:  It had incorrect values for the screen density, both horizontal and vertical. This means it incorrectly scaled dimensions based on physical sizes: pt, mm, and in.  It had Android 2.0 as API level 6 instead of level 5, so version-specific resource directories need to use the -v6 suffix instead of -v5 Both of these bugs are fixed in Android 2.0.1 and later, and no other devices should ship with Android 2.0 or be affected by these bugs. CHAPTER 36: Handling Multiple Screen Sizes 352 . <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="wrap_content" android:padding="2dip". xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" > <ListView android:id="@android:id/list". android:padding="2dip" android:minHeight="?android:attr/listPreferredItemHeight" > <ImageView android:id="@+id/flag" android:layout_width="wrap_content" android:layout_height="wrap_content"