Activity 之 值保存、状态恢复

1.当activity不小心被销毁时保存相关值，重新创建时拿到值：

1. activty销毁时，调用activity的onSaveInstanceState方法保存值
2. 在activity重新创建时调用onRestoreInstanceState或者onCreate方法拿到值

 代码：  
    @Override  
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);   
        //拿值，方式1   
        if(savedInstanceState!=null){  
               String test = savedInstanceState.getString("test");  
        }

    }   
    @Override  
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);  
        //存值   
       outState.putString("test","test");   
    }

    @Override   
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);   
        //拿值，方式2  
        String test = savedInstanceState.getString("test");  
    }

1.1 onRestoreInstanceState方法拿值好处

1. 不需判断onRestoreInstanceState方法中的savedInstanceState是否为空，再拿值，相比onCreate方法中的savedInstanceState则要先判断是否为空，因为第一次启动activity，savedInstanceState为null
2. 官网推荐

2.防止系统配置改变，重新创建Activity

常见场合：弹出软键盘、屏幕旋转

在androidMenifest.xml中对应activity标签配置android:configChanges属性，指定多个值，用”|“分隔