横竖屏切换时,有时候布局文件layout需要重新加载,因此先要销毁Activity对象,再新建;导致状态无法被保存
解决办法

1. 不让旋转屏幕

 <activity android:name=".OtherActivity" 
           android:screenOrientation="portrait">
 </activity>

2. 实现自己处理横竖屏变化，无需系统重启Activity

<activity android:name=".OtherActivity"
          android:configChanges="orientation|keyboardHidden|screenSize">
</activity>

3. 系统处理配置变更

• onSaveInstanceState
• onCreate
• onRestoreInstanceState

什么时候需要保存onSaveInstanceState

• 当点击HOME键(Activity变为后台,系统有可能回收activity,因此需要保存状态)
• 旋转屏幕
• 用户拨打电话
• 按返回键不需要保存状态

视图状态保存

• 控件id要一致,横屏layout与竖屏layout中
• 实现代码如下

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        //!!!!!!!调用父类
        super.onRestoreInstanceState(savedInstanceState);
    }

    @Override
    public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {
         //!!!!!!!调用父类
        super.onSaveInstanceState(outState, outPersistentState);
    }

• TextView源码分析,实现了onRestoreInstance方法

    @Override
    public void onRestoreInstanceState(Parcelable state) {
        if (!(state instanceof SavedState)) {
            super.onRestoreInstanceState(state);
            return;
    ....
   }

    @Override
    public Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();
    .....
   }

因此当我们自定义控件的时候,也需要重写,需要调用父类的
onSaveInstance方法
onRestoreInstance方法

• 实例:onCreate中判断Bundle是否为空,初次创建Activity时,bundle为空

public class OtherActivity extends AppCompatActivity {

    public String name="";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_other);

        //也可以选择放在onRestoreInstanceState  start
        if (savedInstanceState!=null) {
            name=savedInstanceState.getString("name");
        }else{
            name="请输入名字";
        }
        //end
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        //保存状态
        savedInstanceState.putString("name","Zhang");
    }

    @Override
    public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {
        super.onSaveInstanceState(outState, outPersistentState);
    }
}