学步园

SharedPreferences是Android平台上一个轻量级的存储类，主要是保存一些常用的配置比如窗口状态，比如我们可以通过SharedPreferences来判断程序是不是第一次运行。

下面的实例将用于介绍怎样通过SharedPreferences来判断程序是否是第一次运行，其实现思路很简单，通过在SharedPreferences中存储键值表示程序是否第一次运行。代码如下：

public class PreferenceTestMain extends Activity {
        public static final String PREFS_NAME = "MyPrefsFile";
        public static final String FIRST_RUN = "first";
        private boolean first;

        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.main);
                // Restore preferences
                SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
                first = settings.getBoolean(FIRST_RUN, true);
                if (first) {
                        Toast.makeText(this, "The Application is first run",
                                        Toast.LENGTH_LONG).show();
                } else {
                        Toast.makeText(this, "The Application is not first run",
                                        Toast.LENGTH_LONG).show();
                }

        }

        @Override
        protected void onStop() {
                super.onStop();

                // We need an Editor object to make preference changes.
                // All objects are from android.context.Context
                SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
                SharedPreferences.Editor editor = settings.edit();
                if (first) {
                        editor.putBoolean(FIRST_RUN, false);
                }
                // Commit the edits!
                editor.commit();
        }

}

其中在 onCreate
方法中读取，SharedPreferences 信息，在 onStop
中保存 SharedPreferences信息。注意程序的状态信息一般都在 onStop
保存。