单击“后退"按钮后重新创建活动状态

当我成功地将数据保存到onSaveInstanceState方法中的Bundle时，我找不到为什么onCreate方法中的saveInstanceState总是为null的原因.当我在AVD上运行程序并单击后退"按钮(破坏活动)，然后通过单击其图标再次创建它时，保存状态始终为null.这是一个测试此问题的简单程序.

I can't find out why savedInstanceState is always null in the onCreate method when I'm successfully saving data to the Bundle in onSaveInstanceState method. When I'm running my program on AVD and clicking back button(destroying activity) and then creating it again by clicking its icon the saved state is always null. Here is a simple program which tests this problem.

package com.example.myTestApp;

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

public class MyActivity extends Activity {
    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Button button = (Button)findViewById(R.id.button);
        if(savedInstanceState == null){
            button.setText("No");
        }else{
            button.setText("Yes");
        }
    }

    static final String STATE_SCORE = "playerScore";
    static final String STATE_LEVEL = "playerLevel";
    private int mCurrentScore = 1;
    private int mCurrentLevel = 2;


    @Override
    public void onSaveInstanceState(Bundle savedInstanceState) {
        super.onSaveInstanceState(savedInstanceState);

        savedInstanceState.putInt(STATE_SCORE, mCurrentScore);
        savedInstanceState.putInt(STATE_LEVEL, mCurrentLevel);

    }
}

告诉我如何解决这个问题.

Tell me how to solve this problem if possible.