Android中用onSaveInstanceState保存Fragment状态的方法
在Fragment里面,利用onSaveInstanceState保存数据,并可在onActivityCreated里面恢复数据。
publicvoidonActivityCreated(BundlesavedInstanceState){ super.onActivityCreated(savedInstanceState); ... if(savedInstanceState!=null){ //Restorethefragment'sstatehere } } publicvoidonSaveInstanceState(BundleoutState){ super.onSaveInstanceState(outState); //Savethefragment'sstatehere }
在Activity里面,利用onSaveInstanceState保存Fragment实例的数据,并可在onCreate里面恢复数据:
privateFragmentmyFragment; publicvoidonCreate(BundlesavedInstanceState){ ... if(savedInstanceState==null){ //Instantiatefragment }else{ //Restorethefragment'sinstance myFragment=getSupportFragmentManager().getFragment( savedInstanceState,"fragment"); } ... } @Override protectedvoidonSaveInstanceState(BundleoutState){ super.onSaveInstanceState(outState); //Savethefragment'sinstance //fragmentinstancemaybenull if(myFragment!=null){ getSupportFragmentManager().putFragment(outState,"fragment",myFragment); } }
实例
首先看一个步骤,如果是人为关闭Activity或者Fragment,比如点击了后退键,主动关闭当前页面,就会走onPause()-->onStop() -->onDestroy() 而onSaveInstanceState()并不会被调用.onSaveInstanceState()只有在系统即将要自动清理销毁Activity或Fragment前才会调用,比如
1,由于重力感应手机从竖屏变为横屏,
2,手机点击Home键和长按Home键
3,点击电源键锁屏时
4,从当前Activity跳到另一个Activity
5,应用内存不足即将自动销毁时等情况
综合上面的情况,可以看出,onSaveInstanceState() 这个方法适合临时保存一些非永久性的数据.如果要持久化保存数据,就要将操作放在onStop(),onDestroy()这些方法中去.onSaveInstanceState() 适合的是当前Activity或者Fragment一旦被系统自己销毁,应用还能在这之前保存一些必要的数据,并且用户的操作很快又回到当前这个页面,这个时候数据并没有丢失,还能最大程度的恢复之前状态.这就是这个方法最大的意义.下面上例子做个简单示例:
在Fragment中:
//系统自动销毁Fragment前保存必要的数据 @Override publicvoidonSaveInstanceState(BundleoutState){ <spanstyle="white-space:pre"></span>super.onSaveInstanceState(outState); <spanstyle="white-space:pre"></span>Stringcontent=etCon.getText().toString(); <spanstyle="white-space:pre"></span>outState.putString("inputCon",content); } //恢复数据 @Override publicvoidonViewStateRestored(BundlesavedInstanceState){ <spanstyle="white-space:pre"></span>super.onViewStateRestored(savedInstanceState); <spanstyle="white-space:pre"></span>//恢复之前输入框的内容 <spanstyle="white-space:pre"></span>if(savedInstanceState!=null){ <spanstyle="white-space:pre"></span>etCon.setText(savedInstanceState.getString("inputCon","")); } }
在Activity中
//系统自动销毁Activity前保存必要的数据 @Override publicvoidonSaveInstanceState(BundleoutState){ <spanstyle="white-space:pre"></span>super.onSaveInstanceState(outState); Stringcontent=etCon.getText().toString(); outState.putString("inputCon",content); } //Activity中可在onRestoreInstanceState()方法恢复数据,也可以在onCreate()中恢复,因为Activity一旦被销毁就会重走一次onCreate()开始的正常生命周期 @Override publicvoidonRestoreInstanceState(BundlesavedInstanceState){ super.onRestoreInstanceState(savedInstanceState); //恢复之前输入框的内容 if(savedInstanceState!=null){ etCon.setText(savedInstanceState.getString("inputCon","")); } } @Override publicvoidonDestroy(){ super.onDestroy(); //Activity被销毁前可进行最后一次数据的保存,过了这村就没这店了. }
这里有个重要的点,上面的上面所提及的onSaveInstanceState()方法只有在Activity或Fragment确定要被系统自动清除时,才会被调用,如果不是长期后台应用,页面没有被系统kill掉,对应的Activity或Fragment也就不会调用onSaveInstanceState()这些方法.