Android笔记之Activity的生命周期

1.   onCreate, onStart, onResume, onPause, onStop, onRestart, onDestroy

如果连这7个方法都不清楚的话，那么就该从头开始看Android了。下图是Activity的生命周期，加深记忆用：

2、 onSaveInstanceState与onRestoreInstanceState

当设备的配置（横竖屏、语言等）发生变化而使Activity自动重启，或者Activity从前台转到后台（如，按下Home键）的时 候，Activity会调用onSaveInstanceState(Bundle)方法将当前Activity的状态保存到一个Bundle变量中。这 个Bundle变量与onCreate(Bundle)方法和onRestoreInstanceState(Bundle)中的Bundle参数是同一 个，也就是说，后两个方法通过传入的Bundle参数还原Activity的状态。

不过，虽然Activity的状态保存到了Bundle中，但是这些状态数据却无法从Bundle中取出。要想手动地设置一些重启后需要的状态数据，可以直接调用该Bundle实例的putXXX方法存入额外的数据信息。

如下列所示：

public class SaveNRestoreInstanceStateActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.save_restore_state);
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        EditText et1 = (EditText) findViewById(R.id.et1);
        EditText et2 = (EditText) findViewById(R.id.et2);
        
        et1.setText("This is et1");
        et2.setText("This is et2");
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        outState.putString("et1", "This is from outState and this is et1");
        outState.putString("et2", "This is from outState and this is et2");
        
        super.onSaveInstanceState(outState);
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        
        EditText et1 = (EditText) findViewById(R.id.et1);
        EditText et2 = (EditText) findViewById(R.id.et2);
        
        et1.setText(savedInstanceState.getString("et1"));
        et2.setText(savedInstanceState.getString("et2"));
    }

}

3.   onBackPressed

回退键的处理方法，一般用来屏蔽回退键或者在添加后退时的额外功能（弹出确认退出的对话框等）。

原文：http://blog.csdn.net/sadfishsc/article/details/7345738