Android 报错 Activity 状态

浏览数：19 / 时间：2015年06月11日

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：

package 
com.android.hello;
import 
android.app.Activity;
import 
android.os.Bundle;
import 
android.widget.TextView;
public 
class HelloAndroid extends
Activity {
/** Called when the activity is first created. */
@Override
public
void 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);
}
private
TextView 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

@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

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