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随时随地学Java
问题背景：
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最近用到了主Activity里有一个Thread在处理数据，当跳转到第二个Activity时，希望Thread暂停。从第二个Activity回来时这个Thread再接着运行。今天得空顺着这个应用场景再过一下Activity的生命周期。
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下面是一个小demo，主Activity里有个按钮，跳转到第二个Activity。在主Activity里有个UpdateThread在一直运行。第二个Activity里有个按钮，点击显示一个Dialog。下面是源码：
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activity_main.xml
1 2 3 | <relativelayout android:layout_height="match_parent"android:layout_width="match_parent"android:paddingbottom="@dimen/activity_vertical_margin"android:paddingleft="@dimen/activity_horizontal_margin"android:paddingright="@dimen/activity_horizontal_margin"android:paddingtop="@dimen/activity_vertical_margin"tools:context=".MainActivity"xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools">? <textview android:id="@+id/textview_show"?android:layout_height="wrap_content"android:layout_width="wrap_content"?android:text="@string/hello_world"android:textsize="23dip"><button android:id="@+id/button_jump"android:layout_centerinparent="true"?android:layout_height="wrap_content"android:layout_width="wrap_content"?android:text="跳转"android:textsize="23dip"></button></textview></relativelayout> |
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activity_second.xml
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | ????<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"????xmlns:tools="http://schemas.android.com/tools"????android:layout_width="match_parent"????android:layout_height="match_parent"????android:paddingBottom="@dimen/activity_vertical_margin"????android:paddingLeft="@dimen/activity_horizontal_margin"????android:paddingRight="@dimen/activity_horizontal_margin"????android:paddingTop="@dimen/activity_vertical_margin"????tools:context=".SecondActivity"?>? ????<TextView????????android:layout_width="wrap_content"????????android:layout_height="wrap_content"????????android:text="@string/hello_world"?/>????<Button????????android:id="@+id/button_show_dialog"????????android:layout_width="wrap_content"????????android:layout_height="wrap_content"????????android:layout_centerInParent="true"????????android:text="显示Dialog"/>? </RelativeLayout> |
MainActivity.java
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 | ????package?com.example.activitylife;? import?android.app.Activity;import?android.content.Intent;import?android.os.Bundle;import?android.util.Log;import?android.view.Menu;import?android.view.View;import?android.widget.Button;import?android.widget.TextView;? public?class?MainActivity?extends?Activity {????TextView mTextView =?null;????Button mBtutton =?null;????boolean?allowRun =?true;????boolean?allowUpdate =?true;????private?static?final?String tag =?"yan";????@Override????protected?void?onCreate(Bundle savedInstanceState) {????????super.onCreate(savedInstanceState);????????setContentView(R.layout.activity_main);????????initUI();????????Log.i(tag,?"onCreate...");????????mTextView.setText("..................."?+ "");????????mTextView.append("onCreate..."?+ "");????????new?<a title="Thread"?href="http://www.android-study.com/pingtaikaifa/568.html">Thread</a>(new?Update<a title="Thread"href="http://www.android-study.com/pingtaikaifa/568.html">Thread</a>()).start();????}?????? ????@Override????protected?void?onStart() {????????// TODO Auto-generated method stub????????super.onStart();????????Log.i(tag,?"onStart...");????????mTextView.append("onStart..."?+ "");????}? ? ????@Override????protected?void?onRestart() {????????// TODO Auto-generated method stub????????super.onRestart();????????Log.i(tag,?"onRestart...");????????mTextView.append("onRestart..."?+ "");????}? ? ????@Override????protected?void?onResume() {????????// TODO Auto-generated method stub????????super.onResume();????????Log.i(tag,?"onResume...");????????mTextView.append("onResume..."?+ "");????}? ? ????@Override????protected?void?onPause() {????????// TODO Auto-generated method stub????????super.onPause();????????Log.i(tag,?"onPause...");????????mTextView.append("onPause..."?+ "");????}? ? ????@Override????protected?void?onStop() {????????// TODO Auto-generated method stub????????super.onStop();????????Log.i(tag,?"onStop...");????}? ? ????@Override????protected?void?onDestroy() {????????// TODO Auto-generated method stub????????Log.i(tag,?"onDestroy...");????????super.onDestroy();????}? ? ????@Override????public?boolean?onCreateOptionsMenu(Menu menu) {????????// Inflate the menu; this adds items to the action bar if it is present.????????getMenuInflater().inflate(R.menu.main, menu);????????return?true;????}????public?void?initUI(){????????mTextView = (TextView)findViewById(R.id.textview_show);????????mBtutton = (Button)findViewById(R.id.button_jump);????????mBtutton.setOnClickListener(new?View.OnClickListener() {?????????????????????????@Override????????????public?void?onClick(View v) {????????????????// TODO Auto-generated method stub????????????????Intent intent =?new?Intent(MainActivity.this, SecondActivity.class);//????????????? allowRun = false;//????????????? allowUpdate = false;????????????????startActivity(intent);????????????}????????});????}????class?Update<a title="Thread"?href="http://www.android-study.com/pingtaikaifa/568.html">Thread</a>?implements?Runnable{? ????????@Override????????public?void?run() {????????????// TODO Auto-generated method stub????????????while(allowRun){????????????????if(allowUpdate){????????????????????try?{????????????????????????<a title="Thread"?href="http://www.android-study.com/pingtaikaifa/568.html">Thread</a>.sleep(1000);????????????????????????Log.i(tag,?"Update<a title="Thread" href="http://www.android-study.com/pingtaikaifa/568.html">Thread</a>....");????????????????????}?catch?(InterruptedException e) {????????????????????????// TODO Auto-generated catch block????????????????????????e.printStackTrace();????????????????????}?????????????????????????????????????}????????????}????????}?????????????}} |
SecondActivity.java
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 | ????package?com.example.activitylife;? import?android.app.Activity;import?android.app.AlertDialog;import?android.app.Dialog;import?android.content.Context;import?android.content.DialogInterface;import?android.content.DialogInterface.OnClickListener;import?android.os.Bundle;import?android.util.Log;import?android.view.Menu;import?android.view.View;import?android.widget.Button;? public?class?SecondActivity?extends?Activity {????private?final?static?String tag =?"yan";????Button mShowDialogBtn =?null;????@Override????protected?void?onCreate(Bundle savedInstanceState) {????????super.onCreate(savedInstanceState);????????setContentView(R.layout.activity_second);????Log.i(tag,?"SecondActivity:OnCreate...");????mShowDialogBtn = (Button)findViewById(R.id.button_show_dialog);????mShowDialogBtn.setOnClickListener(new?View.OnClickListener() {?????????????????@Override????????public?void?onClick(View v) {????????????// TODO Auto-generated method stub????????????showAlertDialog(SecondActivity.this);????????}????});????}? ????@Override????protected?void?onStart() {????????// TODO Auto-generated method stub????????super.onStart();????????Log.i(tag,?"SecondActivity:onStart...");????}? ????@Override????protected?void?onRestart() {????????// TODO Auto-generated method stub????????super.onRestart();????????Log.i(tag,?"SecondActivity:onRestart...");????}? ????@Override????protected?void?onResume() {????????// TODO Auto-generated method stub????????super.onResume();????????Log.i(tag,?"SecondActivity:onResume...");????}? ????@Override????protected?void?onPause() {????????// TODO Auto-generated method stub????????super.onPause();????????Log.i(tag,?"SecondActivity:onPause...");????}? ????@Override????protected?void?onStop() {????????// TODO Auto-generated method stub????????super.onStop();????????Log.i(tag,?"SecondActivity:onStop...");????}? ????@Override????protected?void?onDestroy() {????????// TODO Auto-generated method stub????????super.onDestroy();????????Log.i(tag,?"SecondActivity onDestroy...");????}? ????@Override????public?boolean?onCreateOptionsMenu(Menu menu) {????????// Inflate the menu; this adds items to the action bar if it is present.????????getMenuInflater().inflate(R.menu.second, menu);????????return?true;????}?????????public?void?showAlertDialog(Context c){????????Dialog dialog =?new?AlertDialog.Builder(c)????????.setTitle("通知")????????.setMessage("专注才能深入 ")????????.setIcon(android.R.drawable.ic_dialog_email)????????.setPositiveButton("确定",?new?OnClickListener() {?????????????????????????@Override????????????public?void?onClick(DialogInterface dialog,?int?which) {????????????????// TODO Auto-generated method stub????????????????dialog.dismiss();????????????}????????})????????.create();????????dialog.show();????}? } |
运行界面:
下面是得到的结论:
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1、一个正常的Activity的流程:onCreate------onStart-----------onResume, onResume的时候就可以看到这个Activity，并跟这个Activity进行交互。之后如果正常退出的话，流程是:onPause--------onStop---------onDestroy.什么时候进行onPause的状态呢？在Activity不在是最前端，但依然可见时这个状态是onPause。所以切换到SecondActivity时，主Activity先进行onPause，当SecondActivity onResume可见时，主Activity进行onStop，表示彻底不可见。 (正常的流程可简化记忆为:CS R, PS D. 有CS和PS打头 ?不会记混淆吧。)
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2、如果不做特别处理，主Activity切换到SecondActivity后，只进行到onStop，如果自己写了finish()，那么从SecondActivity按返回键时就直接退出了，否则的话主Activity进行onRestart--------onStart-----onResume.恢复正常。
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3、当主Activity里有个UpdateThread一直在运行时，即使切换到SecondActivity，它依旧没有被释放，并正常运行。
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如果需要切换到第二个Activity时，UpdateThread停止运行，让allowUpdate = false。当切换回来时，让allowUpdate = true就ok了。
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4、从SecondActivity按返回键时，SecondActivity自动进行了onDestroy.
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5、如果不对主Activity做额外操作，当按返回键后，虽然他执行了onDestroy，但是UpdateThread一直在运行。这点比较奇葩，呵呵。所以要退出主程序时，一定让allowRun = false，确保Thread停止.
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6、当在主Activity复写了OnBackPressed()时：
1 2 3 4 5 6 7 | ????@Overridepublic?void?onBackPressed() {????// TODO Auto-generated method stub????super.onBackPressed();????MainActivity.this.finish();} |
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虽然finish()了，但是UpdateThread依旧在运行。
7、如果对主Activity进行锁屏，它从onResume-----切换到onPause---onStop的状态，不用说，UpdateThread依旧在运行。
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8、当在SecondActivity按显示Dialog时，如上面第三幅图时，对SecondActivity的状态没有任何影响。这一点跟咱家之前的观念还不大一样，往后要更正了。其实可以这样理解，因为Dialog显示的时候，SecondActivity首先是可见的所以肯定不是onStop状态。再者，虽然SecondActivity貌似不在最前端了，但事实上他依旧可以合用户进行交互，在屏幕周围可以响应点击等事件。在本例中，如果不按Dialog的确定按键，而是点击屏幕其他区域一样可以让Dialog消失，所以SecondActivity没有进入onPause状态，而依旧是OnResume.
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链接http://blog.csdn.net/lamp_zy/article/details/7703893说当按锁屏键时，原Activity只执行onPause而不执行onStop这是胡扯。此链接中还说，当有Dialog显示时，当前Activity会进入onPause状态而不进入OnStop状态，这亦是胡扯，真实情况是当有Dialog显示时，原Activity依旧是onResume状态。
这下Activity的生命周期终于真相大白了！！！
关注微信号：javalearns?? 随时随地学Java
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随时随地学Java