Android基础之Activity生命周期

package com.scott.lifecycle;
 
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
 
public class LifeCycleActivity extends Activity {
     
    private static final String TAG = "LifeCycleActivity";
    private Context context = this;
    private int param = 1;
     
    //Activity创建时被调用
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Log.i(TAG, "onCreate called.");
     
    setContentView(R.layout.lifecycle);
     
    Button btn = (Button) findViewById(R.id.btn);
    btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(context, TargetActivity.class);
                startActivity(intent);
            }
        });
  }
   
  //Activity创建或者从后台重新回到前台时被调用
  @Override
  protected void onStart() {
    super.onStart();
    Log.i(TAG, "onStart called.");
  }
   
  //Activity从后台重新回到前台时被调用
  @Override
  protected void onRestart() {
    super.onRestart();
    Log.i(TAG, "onRestart called.");
  }
   
  //Activity创建或者从被覆盖、后台重新回到前台时被调用
  @Override
  protected void onResume() {
    super.onResume();
    Log.i(TAG, "onResume called.");
  }
   
  //Activity窗口获得或失去焦点时被调用,在onResume之后或onPause之后
  /*@Override
  public void onWindowFocusChanged(boolean hasFocus) {
    super.onWindowFocusChanged(hasFocus);
    Log.i(TAG, "onWindowFocusChanged called.");
  }*/
   
  //Activity被覆盖到下面或者锁屏时被调用
  @Override
  protected void onPause() {
    super.onPause();
    Log.i(TAG, "onPause called.");
    //有可能在执行完onPause或onStop后,系统资源紧张将Activity杀死,所以有必要在此保存持久数据
  }
   
  //退出当前Activity或者跳转到新Activity时被调用
  @Override
  protected void onStop() {
    super.onStop();
    Log.i(TAG, "onStop called.");   
  }
   
  //退出当前Activity时被调用,调用之后Activity就结束了
  @Override
  protected void onDestroy() {
    super.onDestroy();
    Log.i(TAG, "onDestory called.");
  }
   
  /**
   * Activity被系统杀死时被调用.
   * 例如:屏幕方向改变时,Activity被销毁再重建;当前Activity处于后台,系统资源紧张将其杀死.
   * 另外,当跳转到其他Activity或者按Home键回到主屏时该方法也会被调用,系统是为了保存当前View组件的状态.
   * 在onPause之前被调用.
   */
    @Override
    protected void onSaveInstanceState(Bundle outState) {
        outState.putInt("param", param);
        Log.i(TAG, "onSaveInstanceState called. put param: " + param);
        super.onSaveInstanceState(outState);
    }
     
    /**
     * Activity被系统杀死后再重建时被调用.
     * 例如:屏幕方向改变时,Activity被销毁再重建;当前Activity处于后台,系统资源紧张将其杀死,用户又启动该Activity.
     * 这两种情况下onRestoreInstanceState都会被调用,在onStart之后.
     */
    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        param = savedInstanceState.getInt("param");
        Log.i(TAG, "onRestoreInstanceState called. get param: " + param);
        super.onRestoreInstanceState(savedInstanceState);
    }
}

package com.scott.lifecycle;
 
import android.app.Activity;
import android.content.res.Configuration;
import android.os.Bundle;
import android.util.Log;
 
public class OrientationActivity extends Activity {
     
    private static final String TAG = "OrientationActivity";
    private int param = 1;
     
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.orientation_portrait);
        Log.i(TAG, "onCreate called.");
    }
     
    @Override
    protected void onStart() {
        super.onStart();
        Log.i(TAG, "onStart called.");
    }
     
    @Override
    protected void onRestart() {
        super.onRestart();
        Log.i(TAG, "onRestart called.");
    }
     
    @Override
    protected void onResume() {
        super.onResume();
        Log.i(TAG, "onResume called.");
    }
     
    @Override
    protected void onPause() {
        super.onPause();
        Log.i(TAG, "onPause called.");
    }
     
    @Override
    protected void onStop() {
        super.onStop();
        Log.i(TAG, "onStop called.");
    }
     
    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i(TAG, "onDestory called.");
    }
 
    @Override
    protected void onSaveInstanceState(Bundle outState) {
        outState.putInt("param", param);
        Log.i(TAG, "onSaveInstanceState called. put param: " + param);
        super.onSaveInstanceState(outState);
    }
     
    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        param = savedInstanceState.getInt("param");
        Log.i(TAG, "onRestoreInstanceState called. get param: " + param);
        super.onRestoreInstanceState(savedInstanceState);
    }
     
    //当指定了android:configChanges="orientation"后,方向改变时onConfigurationChanged被调用
    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        Log.i(TAG, "onConfigurationChanged called.");
        switch (newConfig.orientation) {
        case Configuration.ORIENTATION_PORTRAIT:
            setContentView(R.layout.orientation_portrait);
            break;
        case Configuration.ORIENTATION_LANDSCAPE:
            setContentView(R.layout.orientation_landscape);
            break;
        }
    }
}