在Android开发中，第一步学习的应该是最基础的东西，即Activity的声明周期，相信Activity对于从事Android开发的朋友都很熟悉，这里作者不多做解释。Android的生命周期可以用如下所示的图来说明（此图来自A）：由图示可以看出，Android应用程序从运行到结束要先后经历六个过程，第一个：onCreate（）就是对应用程序进行初次创建所回调的函数，一般在这个函数中初始化应用程序的界面，第二个和第三个分别是启动应用时所回调的函数，之后应用程序进入Activity running状态。接着如果有其他的Activity挡住前一个Activity，但是并没有完全挡住的时候，即前一个Activity失去了焦点，此时onPause（）回调，当另一个Activity完全挡住前一个Activity的时候，此时回调函数onStop（），如果此时退出程序或者是调用函数finish（），那么Activity进入onDestory（）阶段，图中的反向箭头指的是在某一种情况下的Activity的反应，在这里不多做解释。为了更清楚的说明这个问题，一下是测试代码，以供参考：
public class Life_Test extends Activity {private Button button;private Button button2;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_life__test);Log.d("Debug", "onCreate");button=(Button)findViewById(R.id.button1);button2=(Button)findViewById(R.id.button2);button.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubAlertDialog.Builder builder=new Builder(Life_Test.this);builder.setTitle("Test...");builder.setMessage("This is Test_Dialg..");builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {// TODO Auto-generated method stubdialog.dismiss();}});builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {// TODO Auto-generated method stubdialog.dismiss();}});builder.show();}});button2.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View arg0) {// TODO Auto-generated method stubfinal Intent intent=new Intent(Life_Test.this,Activity02.class);startActivity(intent);}});}@Overrideprotected void onStart() {// TODO Auto-generated method stubsuper.onStart();Log.d("Debug", "onStart");}@Overrideprotected void onDestroy() {// TODO Auto-generated method stubsuper.onDestroy();Log.d("Debug", "onDestroy");}@Overrideprotected void onPause() {// TODO Auto-generated method stubsuper.onPause();Log.d("Debug", "onPause");}@Overrideprotected void onRestart() {// TODO Auto-generated method stubsuper.onRestart();Log.d("Debug", "onRestart");}@Overrideprotected void onResume() {// TODO Auto-generated method stubsuper.onResume();Log.d("Debug", "onResume");}@Overrideprotected void onStop() {// TODO Auto-generated method stubsuper.onStop();Log.d("Debug", "onStop");}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.activity_life__test, menu);return true;}}
public class Activity02 extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);setContentView(R.layout.activity02);Log.d("Debug2", "------>oncreate");}@Overrideprotected void onStart() {// TODO Auto-generated method stubsuper.onStart();Log.d("Debug2", "------>onstart");}@Overrideprotected void onDestroy() {// TODO Auto-generated method stubsuper.onDestroy();Log.d("Debug2", "------>ondestory");}@Overrideprotected void onPause() {// TODO Auto-generated method stubsuper.onPause();Log.d("Debug2", "------>onpause");}@Overrideprotected void onRestart() {// TODO Auto-generated method stubsuper.onRestart();Log.d("Debug2", "------>onrestart");}@Overrideprotected void onResume() {// TODO Auto-generated method stubsuper.onResume();Log.d("Debug2", "------>onresume");}@Overrideprotected void onStop() {// TODO Auto-generated method stubsuper.onStop();Log.d("Debug2", "------>onstop");}}
到此Activity的生命周期就介绍完毕了。
