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Before the addOverlay() method is called

Add this at the top of the HelloItemizedOverlay class

When the class is nested in the NoteEditor class, this technique will not work.

MergeAdapter accepts a mix of Adapters and Views and presents them as one contiguous whole to whatever ListView it is poured into. This is good for cases where you have multiple data sources, or if you have a handful of ordinary Views to mix in with lists of data, or the like.

Android 的某些功能着实让人喜爱，而另一些尚需改进。我们觉得 Google 应该改进的一个地方就是 Android 的待机锁定屏幕的可用性。Android 的优秀的小工具框架能让它在一瞥之间提供不少信息。现在的这个空旷的锁定屏幕一定可以得到增强（这对于平板电脑来说非常合适），而多亏了一些应用程序，Android 可以做到这一点

按我理解，layout_gravity 属性是用于设置View 与其容器的对齐关系的，但实际使用中 却发现 似乎不是这样，请看如下代码： <?xml version="1.0" encoding="utf-8"?> <LinearLayout     xmlns:android="http://schemas.android.com/apk/res/android"     android:orientation="vertical"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     android:background="#AA009988">     <TextView         android:id="@+id/my_view"         android:layout_width="220dip"         android:layout_height="100dip"         android:text="sdfasdfsdfsdf\nsdfjlwjesd"         android:background="#889900AA"         *android:layout_gravity="center"* /> </LinearLayout> 我为 TextView 设置了 *layout_gravity="center"*- ，本来它应该在父容器中 垂直和水平 居中的，但事实上只是水平居中了，垂直方向并未居中。 我再进一步通过 *layout_gravity="**center_vertical**"* ，但仍然无法垂直居中，请问这是为什么呢？

你可以在最外面的 LinearLayout 加上android:gravity="center". Vertical LinearLayout中， layout_gravity 设置成center无法垂直剧中，是因 为container的排版被限制为从上到下, 试想一下，如果按照你的逻辑，假设第一个child layout_gravity设置成bottom,   第二个childlayout_gravity设置成top,  那么第一个就会跑到第二个下面了。 所以， 当你设置整个linearlayout为垂直， layout_gravity中， 只有 left, right, center_ horizontal 管用的。 tj

Adds multi-touch zoom to; ImageViews, WebViews, and MapViews. Simply use the corresponding object in place of the default, and the "pinch" functionality will be usable. Also includes misc. Views which can be useful for development.

// go full screen WindowManager.LayoutParams attrs = mActivity.getWindow().getAttributes (); attrs.flags |= WindowManager.LayoutParams.FLAG_FULLSCREEN; mActivity.getWindow().setAttributes(attrs); // go non-full screen WindowManager.LayoutParams attrs = mActivity.getWindow().getAttributes (); attrs.flags &= (~WindowManager.LayoutParams.FLAG_FULLSCREEN); mActivity.getWindow().setAttributes(attrs);

1. you can look at the video from Google IO conference 2009, called Turbo charging your UI's by Romain Guy; he discussed some of the optimizations you can do when working with ListViews. 2. You can read Mark Murphy's series of ListView tutorials at android guys titled Fancy ListViews: http://www.google.co.in/url?sa=t&source=web&ct=res&cd=4&ved=0CBYQFjAD...

spnCountries.setAdapter(aspnCountries); spnCountries.setOnItemSelectedListener(spnCountriesListener); private Spinner.OnItemSelectedListener spnCountriesListener =   new Spinner.OnItemSelectedListener() {     public void onItemSelected(AdapterView parent, View v, int position, long id) {       Log.i("print", parent.getSelectedItem().toString());     }     public void onNothingSelected(AdapterView parent) { }              };

But in practice, you will notice that the AsyncTask is limited to 10 threads. This number is hardcoded somewhere in the Android SDK so we cannot change this. In this case it’s a limitation we cannot live with, because often more than 10 images are loaded at the same time.

I’ve shown you how to improve performance of a ListView in three different ways: By loading images in a seperate thread By reusing rows in the list By caching views within a row

As part of my job, I ran into memory leaks issues in Android applications and they are most of the time due to the same mistake: keeping a long-lived reference to a Context.

There are two easy ways to avoid context-related memory leaks. The most obvious one is to avoid escaping the context outside of its own scope. The example above showed the case of a static reference but inner classes and their implicit reference to the outer class can be equally dangerous. The second solution is to use the Application context. This context will live as long as your application is alive and does not depend on the activities life cycle. If you plan on keeping long-lived objects that need a context, remember the application object. You can obtain it easily by calling Context.getApplicationContext() or Activity.getApplication().

In summary, to avoid context-related memory leaks, remember the following: Do not keep long-lived references to a context-activity (a reference to an activity should have the same life cycle as the activity itself) Try using the context-application instead of a context-activity Avoid non-static inner classes in an activity if you don't control their life cycle, use a static inner class and make a weak reference to the activity inside. The solution to this issue is to use a static inner class with a WeakReference to the outer class, as done in ViewRoot and its W inner class for instance A garbage collector is not an insurance against memory leaks

Removing the window's background can be achieved very easily by using a custom theme. To do so, first create a file called res/values/theme.xml containing the following:

<resources>    <style name="Theme.NoBackground" parent="android:Theme">        <item name="android:windowBackground">@null</item>    </style></resources>

You then need to apply the theme to your activity by adding the attribute android:theme="@style/Theme.NoBackground" to your <activity /> or <application /> tag. This trick comes in very handy for any app that uses a MapView, a WebView or any other full screen opaque view.

// Get display for detecting the phone orientation display = ((WindowManager) getSystemService(WINDOW_SERVICE)).getDefaultDisplay(); // Get the orientation int orientation = display.getOrientation();

android.view.Display class provide a simple way to determine the phone orientation.