學習筆記之ViewPager

轉載請註明出處 
[我的博客]http://www.lostbug.com

今天看ViewPager的官方文檔，官方做了一個ActionBar tabs和Fragment組合的例子 
在 class TabsAdapter extends FragmentPagerAdapter中 
有一句代碼，沒怎麼見過

  @Override
        public Fragment getItem(int position) {
            TabInfo info = mTabs.get(position);
            return Fragment.instantiate(mContext, info.clss.getName(), info.args);
        }

就是這個通過ClassName獲取Fragment的方法，這是源代碼：

/**
     * Create a new instance of a Fragment with the given class name.  This is
     * the same as calling its empty constructor.
     *
     * @param context The calling context being used to instantiate the fragment.
     * This is currently just used to get its ClassLoader.
     * @param fname The class name of the fragment to instantiate.
     * @param args Bundle of arguments to supply to the fragment, which it
     * can retrieve with {@link #getArguments()}.  May be null.
     * @return Returns a new fragment instance.
     * @throws InstantiationException If there is a failure in instantiating
     * the given fragment class.  This is a runtime exception; it is not
     * normally expected to happen.
     */
    public static Fragment instantiate(Context context, String fname, @Nullable Bundle args) {
        try {
            Class<?> clazz = sClassMap.get(fname);
            if (clazz == null) {
                // Class not found in the cache, see if it's real, and try to add it
                clazz = context.getClassLoader().loadClass(fname);
                if (!Fragment.class.isAssignableFrom(clazz)) {
                    throw new InstantiationException("Trying to instantiate a class " + fname
                            + " that is not a Fragment", new ClassCastException());
                }
                sClassMap.put(fname, clazz);
            }
            Fragment f = (Fragment)clazz.newInstance();
            if (args != null) {
                args.setClassLoader(f.getClass().getClassLoader());
                f.mArguments = args;
            }
            return f;
        } catch (ClassNotFoundException e) {
            throw new InstantiationException("Unable to instantiate fragment " + fname
                    + ": make sure class name exists, is public, and has an"
                    + " empty constructor that is public", e);
        } catch (java.lang.InstantiationException e) {
            throw new InstantiationException("Unable to instantiate fragment " + fname
                    + ": make sure class name exists, is public, and has an"
                    + " empty constructor that is public", e);
        } catch (IllegalAccessException e) {
            throw new InstantiationException("Unable to instantiate fragment " + fname
                    + ": make sure class name exists, is public, and has an"
                    + " empty constructor that is public", e);
        }
    }

不多說啦，我只是菜