Android--->activity高级运用，保存前一个界面为完成的数据savedInstanceState。

main.xml布局代码分析

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <TextView  
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        android:text="@string/hello"
        />
    <EditText
        android:id="@+id/txt"
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:text=""
        />
    <Button
        android:id="@+id/secondBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Second"
        />
</LinearLayout>

second.xml布局文件代码分析

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="SecondActivity"
    />
</LinearLayout>

main.xml所对应的操作代码MainActivity.java

package com.szy.activity;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends Activity
{
    private final static String TAG="MainActivity";
    private static final String CONTENT = "content";
    private Button secondBtn=null;
    private EditText txt = null;
    
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        txt=(EditText)findViewById(R.id.txt);
        //还原保存的数据
        if (null!=savedInstanceState&&savedInstanceState.containsKey(CONTENT))
        {
            txt.setText(savedInstanceState.getString(CONTENT));
        }
        secondBtn=(Button)findViewById(R.id.secondBtn);
        secondBtn.setOnClickListener(listener);
        Log.i(TAG, "MainActivity-->onCreate");
    }

    @Override
    protected void onDestroy()
    {
        super.onDestroy();
        Log.i(TAG, "MainActivity-->onDestroy");
    }

    @Override
    protected void onPause()
    {
        super.onPause();
        Log.i(TAG, "MainActivity-->onPause");
    }

    @Override
    protected void onRestart()
    {
        super.onRestart();
        Log.i(TAG, "MainActivity-->onRestart");
    }

    @Override
    protected void onResume()
    {
        super.onResume();
        Log.i(TAG, "MainActivity-->onResume");
    }

    @Override
    protected void onStart()
    {
        super.onStart();
        Log.i(TAG, "MainActivity-->onStart");
    }

    @Override
    protected void onStop()
    {
        super.onStop();
        Log.i(TAG, "MainActivity-->onStop");
    }
    
    //保存状态及数据到content
    protected void onSaveInstanceState(Bundle outState)
    {
        super.onSaveInstanceState(outState);
        Log.i(TAG, "MainActivity-->onSaveInstanceState");
        String content=txt.getText().toString();
        outState.putString(CONTENT, content);
    }

    private OnClickListener listener=new OnClickListener()
    {
        
        public void onClick(View v)
        {
            Button btn=(Button)v;
            Intent intent=new Intent();
            switch (btn.getId())
            {
            case R.id.secondBtn:
                intent.setClass(MainActivity.this, SecondActivity.class);
                break;
            }
            startActivity(intent);
        }
        
    };
    
}

second.xml布局文件所对应的操作SecondActivity.java

package com.szy.activity;

import android.app.Activity;
import android.os.Bundle;

public class SecondActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.second);
    }

    @Override
    protected void onDestroy()
    {
        super.onDestroy();
    }

    @Override
    protected void onPause()
    {
        super.onPause();
    }

    @Override
    protected void onRestart()
    {
        super.onRestart();
    }

    @Override
    protected void onResume()
    {
        super.onResume();
    }

    @Override
    protected void onStart()
    {
        super.onStart();
    }

    @Override
    protected void onStop()
    {
        super.onStop();
    }
}

activity布局界面需要在AndroidManifest.xml注册一下

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.szy.activity"
      android:versionCode="1"
      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="8" />

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".MainActivity"
                  android:label="@string/app_name"
                  android:theme="@android:style/Theme.Wallpaper"
                  >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".SecondActivity"
                  android:label="@string/app_name">
        </activity>
        <activity android:name=".ThirdActivity"
                  android:label="@string/app_name"
                  android:theme="@android:style/Theme.Dialog">
        </activity>
    </application>
</manifest>