Android 报错 Activity 状态

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我近期学习了一下android sdk,不太清楚里面的一些原理，如何保存应用程序的状态，看下面hello的小例子：

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package com.android.hello;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class HelloAndroid extendsActivity {
/** Called when the activity is first created. */
@Override
publicvoid onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mTextView =new TextView(this);
if(savedInstanceState == null) {
mTextView.setText("Welcome to HelloAndroid!");
}else {
mTextView.setText("Welcome back.");
}
setContentView(mTextView);
}
privateTextView mTextView = null;
}

这个android 小例子应该是每个人都开发过的，我每次关闭程序再打开是都是给我显示第一个Welcome to HelloAndroid ，我想在第二次访问的时候能够显示 Welcome back，我该如何处理？

处理方法

你需要重写 onSaveInstanceState(Bundle savedInstanceState)，把你想要保存的状态写入到 Bundle 中，如下

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@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
// Save UI state changes to the savedInstanceState.
// This bundle will be passed to onCreate if the process is
// killed and restarted.
savedInstanceState.putBoolean("MyBoolean",true);
savedInstanceState.putDouble("myDouble",1.9);
savedInstanceState.putInt("MyInt",1);
savedInstanceState.putString("MyString","Welcome back to Android");
// etc.
}

Bundle 的本质是键值对的方式存储，你可以通过 onCreate()和 onRestoreInstanceState() 或的对应的值

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@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
booleanmyBoolean = savedInstanceState.getBoolean("MyBoolean");
doublemyDouble = savedInstanceState.getDouble("myDouble");
intmyInt = savedInstanceState.getInt("MyInt");
String myString = savedInstanceState.getString("MyString");
}

您通常会使用这项技术来存储实例的值的应用程序（选择，未保存的文本等）。

原文地址：http://www.itmmd.com/201410/38.html
该文章由萌萌的IT人整理发布,转载须标明出处。

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