Activity的onSaveInstanceState()和 onRestoreInstanceState()方法
2014-07-26 11:17
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Activity的onSaveInstanceState()和 onRestoreInstanceState()方法
Activity的 onSaveInstanceState() 和 onRestoreInstanceState()并不是生命周期方法,它们不同于 onCreate()、onPause()等生命周期方法,它们并不一定会被触发。当应用遇到意外情况(如:内存不足)由系统销毁一个Activity时,onSaveInstanceState() 会被调用。但是当用户主动去销毁一个Activity时,例如在应用中按返回键,onSaveInstanceState()就不会被调用。因为在这种情况下,用户的行为决定了不需要保存Activity的状态。通常onSaveInstanceState()只适合用于保存一些临时性的状态,而onPause()适合用于数据的持久化保存。
另外,当屏幕的方向发生了改变, Activity会被摧毁并且被重新创建,如果你想在Activity被摧毁前缓存一些数据,并且在Activity被重新创建后恢复缓存的数据。可以重写Activity的 onSaveInstanceState() 和 onRestoreInstanceState()方法.
注意:在Activity的onCreate(Bundle savedInstanceState)方法里面,该方法的参数与onRestoreInstanceState()方法中的参数一致,因此在onCreate()方法中也能恢复缓存的数据。
如下:
public class PreferencesActivity extends Activity { private String name; protected void onRestoreInstanceState(Bundle savedInstanceState) { name = savedInstanceState.getString("name"); //被重新创建后恢复缓存的数据 super.onRestoreInstanceState(savedInstanceState); } protected void onSaveInstanceState(Bundle outState) { outState.putString("name", "liming");//被摧毁前缓存一些数据 super.onSaveInstanceState(outState); } }
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