大家好,又见面了,我是你们的朋友全栈君。
StrictMode类是Android 2.3 (API 9)引入的一个工具类,可以用来帮助开发者发现代码中的一些不规范的问题。比如,如果你在UI线程中进行了网络或者磁盘操作,StrictMode就会通过Log(logcat )或者对话框的方式把信息提示给你,因为让你的UI线程处理这里操作会被认为是不规范的做法,可能会让你的应用变得比较卡顿。
官网文档:http://developer.android.com/reference/android/os/StrictMode.html
如何启用 StrictMode
我们通常在 Activity 或者自定义的Application类中启动 StrictMode,代码如下:
public void onCreate() {
if (DEVELOPER_MODE) {
StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
.detectDiskReads()
.detectDiskWrites()
.detectNetwork() // or .detectAll() for all detectable problems
.penaltyLog()
.build());
StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder()
.detectLeakedSqlLiteObjects()
.detectLeakedClosableObjects()
.penaltyLog()
.penaltyDeath()
.build());
}
super.onCreate();
}
注意:我们只需要在app的开发版本下使用 StrictMode,线上版本避免使用 StrictMode,随意需要通过 诸如 DEVELOPER_MODE 这样的配置变量来进行控制。
下面我们举几个例子来说明 StrictMode 是如何发挥作用的。
代码1:
public class ActivitySimple extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
StrictMode.setThreadPolicy(new ThreadPolicy.Builder()
.detectAll()
.penaltyDialog() //弹出违规提示对话框
.penaltyLog() //在Logcat 中打印违规异常信息
.build());
this.testNetwork();
}
private void testNetwork() {
try {
URL url = new URL("http://www.baidu.com");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.connect();
BufferedReader reader = new BufferedReader(new InputStreamReader(
conn.getInputStream()));
String lines = null;
StringBuffer sb = new StringBuffer();
while ((lines = reader.readLine()) != null) {
sb.append(lines);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
在这里例子中,我们在主线程(UI线程)中执行了网络请求,ThreadPolicy 策略中的 detectAll()
方法 包含而来对这类违规操作的检查,同时我们通过penaltyDialog()
和 penaltyLog()
两个方法将违规信息提示给开发者。
在运行这段代码是,我们会看到下图中的对话框提示:
在LogCat 中我们会看到这样的日志信息:
... D/StrictMode(26365): StrictMode policy violation; ~duration=58 ms: android.os.StrictMode$StrictModeNetworkViolation: policy=63 violation=4
... D/StrictMode(26365): at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1134)
... D/StrictMode(26365): at libcore.io.BlockGuardOs.recvfrom(BlockGuardOs.java:163)
... D/StrictMode(26365): at libcore.io.IoBridge.recvfrom(IoBridge.java:557)
... D/StrictMode(26365): at java.net.PlainSocketImpl.read(PlainSocketImpl.java:490)
... D/StrictMode(26365): at java.net.PlainSocketImpl.access$000(PlainSocketImpl.java:46)
...
(后面的部分省略)
StrictMode 详解
StrictMode 通过策略方式来让你自定义需要检查哪方面的问题。 主要有两中策略,一个时线程方策略(ThreadPolicy),一个是VM方面的策略(VmPolicy)。
-
ThreadPolicy 主要用于发现在UI线程中是否有读写磁盘的操作,是否有网络操作,以及检查UI线程中调用的自定义代码是否执行得比较慢。
-
VmPolicy,主要用于发现内存问题,比如 Activity内存泄露, SQL 对象内存泄露, 资源未释放,能够限定某个类的最大对象数。
ThreadPolicy 详解
StrictMode.ThreadPolicy.Builder 主要方法如下:
-
detectNetwork() 用于检查UI线程中是否有网络请求操作,上面的代码的就是网络请求违规的问题。
-
detectDiskReads() 和 detectDiskReads() 是磁盘读写检查,触发时会打印出如下日志(以 detectDiskReads() 为例):
... D/StrictMode(27429): StrictMode policy violation; ~duration=33 ms: android.os.StrictMode$StrictModeDiskReadViolation: policy=31 violation=2 ... D/StrictMode(27429): at android.os.StrictMode$AndroidBlockGuardPolicy.onReadFromDisk(StrictMode.java:1118) ... D/StrictMode(27429): at libcore.io.BlockGuardOs.open(BlockGuardOs.java:106) ... D/StrictMode(27429): at java.io.File.createNewFile(File.java:941) ... D/StrictMode(27429): at com.ap.teststrictmode.ActivityTestDisk.testWriteDisk(ActivityTestDisk.java:51) ... D/StrictMode(27429): at com.ap.teststrictmode.ActivityTestDisk.onCreate(ActivityTestDisk.java:40) ... D/StrictMode(27429): at android.app.Activity.performCreate(Activity.java:5122) ... D/StrictMode(27429): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1081) ... D/StrictMode(27429): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270) ... (后面的部分省略)
detectCustomSlowCalls() 主要用于帮助开发者发现UI线程调用的那些方法执行得比较慢,要和
StrictMode.noteSlowCall
配合使用,StrictMode.noteSlowCall
只有通过StrictMode.noteSlowCall
用来标记“可能会”执行比较慢的方法,只有标记过的方法才能被检测到,日志中会记录方法的执行时间(比如 ~duration=2019 ms)。看下面的例子:
代码2:public class ActivityTestDetectCustomSlowCalls extends Activity {
private TextView textView = null;
private static boolean isStrictMode = false;
@Overrideprotected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activitymain); this.textView = (TextView) findViewById(R.id.textview); this.textView.setText("In ActivityTestDetectCustomSlowCalls"); if(! isStrictMode){ StrictMode.setThreadPolicy(new ThreadPolicy.Builder() .detectCustomSlowCalls() .penaltyLog() .build()); isStrictMode = true; } this.slowCall1(); this.slowCall2();}
/* * 没有标记的方法 */ private void slowCall_1(){ //用来标记潜在执行比较慢的方法 SystemClock.sleep(1000 2);}
/ * 标记过的方法 / private void slowCall_2(){ //用来标记潜在执行比较慢的方法 StrictMode.noteSlowCall("slowCall 2"); SystemClock.sleep(1000 2); } }
在logcat 中我们只能看到和方法slowCall_2()
(因为通过StrictMode.noteSlowCall()
标记过)相关的日志:
...: D/StrictMode(1349): StrictMode policy violation; **~duration=2019 ms: android.os.StrictMode$StrictModeCustomViolation: policy=24 violation=8 msg=slowCall 2 ...: D/StrictMode(1349): at android.os.StrictMode$AndroidBlockGuardPolicy.onCustomSlowCall(StrictMode.java:1105) ...: D/StrictMode(1349): at android.os.StrictMode.noteSlowCall(StrictMode.java:1903) ...: D/StrictMode(1349): at com.ap.teststrictmode.ActivityTestDetectCustomSlowCalls.slowCall_2(ActivityTestDetectCustomSlowCalls.java:52) ...: D/StrictMode(1349): at com.ap.teststrictmode.ActivityTestDetectCustomSlowCalls.onCreate(ActivityTestDetectCustomSlowCalls.java:35) ...: D/StrictMode(1349): at android.app.Activity.performCreate(Activity.java:5122) ...: D/StrictMode(1349): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1081) ...: D/StrictMode(1349): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270) ...: D/StrictMode(1349): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2358) ...: D/StrictMode(1349): at android.app.ActivityThread.access$600(ActivityThread.java:156) ...: D/StrictMode(1349): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1340) ...: D/StrictMode(1349): at android.os.Handler.dispatchMessage(Handler.java:99) ...: D/StrictMode(1349): at android.os.Looper.loop(Looper.java:153) ... (后面的部分省略)
当然你也可以在其他线程中使用 detectCustomSlowCalls(),但是没有什么实际意义,也看不到方法执行时间,比如:
public class ActivityTestDetectCustomSlowCalls extends Activity { private TextView textView = null; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); this.textView = (TextView) findViewById(R.id.text_view); this.textView.setText("In ActivityTestDetectCustomSlowCalls"); new Thread(){ public void run() { StrictMode.setThreadPolicy(new ThreadPolicy.Builder() .detectCustomSlowCalls() .penaltyLog() .build()); this.slowCallInCustomThread(); }; private void slowCallInCustomThread(){ //用来标记潜在执行比较慢的方法 StrictMode.noteSlowCall("slowCallInCustomThread"); SystemClock.sleep(1000 * 2); } }.start();; }}
日志输出如下:
...: D/StrictMode(2418): StrictMode policy violation: android.os.StrictMode$StrictModeCustomViolation: policy=24 violation=8 msg=slowCallInCustomThread ...: D/StrictMode(2418): at android.os.StrictMode$AndroidBlockGuardPolicy.onCustomSlowCall(StrictMode.java:1105) ...: D/StrictMode(2418): at android.os.StrictMode.noteSlowCall(StrictMode.java:1903) ...: D/StrictMode(2418): at com.ap.teststrictmode.ActivityTestDetectCustomSlowCalls$1.slowCallInCustomThread(ActivityTestDetectCustomSlowCalls.java:35) ...: D/StrictMode(2418): at com.ap.teststrictmode.ActivityTestDetectCustomSlowCalls$1.run(ActivityTestDetectCustomSlowCalls.java:30) ... (后面的部分省略)
-
penaltyDeath(),当触发违规条件时,直接Crash掉当前应用程序。
-
penaltyDeathOnNetwork(),当触发网络违规时,Crash掉当前应用程序。
-
penaltyDialog(),触发违规时,显示对违规信息对话框。
-
penaltyFlashScreen(),会造成屏幕闪烁,不过一般的设备可能没有这个功能。
-
penaltyDropBox(),将违规信息记录到 dropbox 系统日志目录中(/data/system/dropbox),你可以通过如下命令进行插件:
adb shell dumpsys dropbox dataappstrictmode --print
会得到如下的信息:
2014-05-04 14:56:32 dataappstrictmode (text, 2627 bytes) Process: com.ap.teststrictmode Flags: 0x40a8be46 Package: com.ap.teststrictmode v1 (1.0) Build: Xiaomi/pisces/pisces:4.2.1/JOP40D/JXCCNBA13.0:user/release-keys System-App: false Uptime-Millis: 66679049 Loop-Violation-Number: 10 Duration-Millis: 24 android.os.StrictMode$StrictModeNetworkViolation: policy=191 violation=4 at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1136) at libcore.io.BlockGuardOs.recvfrom(BlockGuardOs.java:163) at libcore.io.IoBridge.recvfrom(IoBridge.java:513) at java.net.PlainSocketImpl.read(PlainSocketImpl.java:488) at java.net.PlainSocketImpl.access$000(PlainSocketImpl.java:46) at java.net.PlainSocketImpl$PlainSocketInputStream.read(PlainSocketImpl.java:240) at java.io.InputStream.read(InputStream.java:163) at java.io.BufferedInputStream.fillbuf(BufferedInputStream.java:142) at java.io.BufferedInputStream.read(BufferedInputStream.java:227) at libcore.io.Streams.readAsciiLine(Streams.java:201) at libcore.net.http.ChunkedInputStream.readChunkSize(ChunkedInputStream.java:77) at libcore.net.http.ChunkedInputStream.read(ChunkedInputStream.java:68) at java.io.InputStream.read(InputStream.java:163) at java.util.zip.InflaterInputStream.fill(InflaterInputStream.java:200) at java.util.zip.InflaterInputStream.read(InflaterInputStream.java:154) at java.util.zip.GZIPInputStream.read(GZIPInputStream.java:167) ...
permitCustomSlowCalls()、permitDiskReads ()、permitDiskWrites()、permitNetwork: 如果你想关闭某一项检测,可以使用对应的permit*方法。
VMPolicy 详解
- detectActivityLeaks() 用户检查 Activity 的内存泄露情况,比如下面的代码:
public class ActivityTestActivityLeaks extends Activity {
private static boolean isStrictMode = false;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(! isStrictMode){
StrictMode.setVmPolicy(new VmPolicy.Builder()
.detectActivityLeaks()
.penaltyLog()
.build());
isStrictMode = true;
}
new Thread() {
@Override
public void run() {
while (true) {
SystemClock.sleep(1000);
}
}
}.start();
}
}
我们反复旋转屏幕就会输出如下信息(重点在 instances=4; limit=1 这一行):
...: E/StrictMode(4784): class com.ap.teststrictmode.ActivityTestActivityLeaks; instances=4; limit=1 ...: E/StrictMode(4784): android.os.StrictMode$InstanceCountViolation: class com.ap.teststrictmode.ActivityTestActivityLeaks; instances=4; limit=1 ...: E/StrictMode(4784): at android.os.StrictMode.setClassInstanceLimit(StrictMode.java:1)
这时因为,我们在Activity中创建了一个Thread匿名内部类,而匿名内部类隐式持有外部类的引用。而每次旋转屏幕是,Android会新创建一个Activity,而原来的Activity实例又被我们启动的匿名内部类线程持有,所以不会释放,从日志上看,当先系统中该Activty有4个实例,而限制是只能创建1各实例。我们不断翻转屏幕,instances 的个数还会持续增加。
- detectLeakedClosableObjects() 和 detectLeakedSqlLiteObjects(),资源没有正确关闭时回触发,比如下面的代码:
public class MainActivityTestDetectLeakedClosableObjects extends Activity {
private static boolean isStrictMode = false;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(! isStrictMode){
StrictMode.setVmPolicy(new VmPolicy.Builder()
.detectLeakedClosableObjects()
.penaltyLog()
.build());
isStrictMode = true;
}
File newxmlfile = new File(Environment.getExternalStorageDirectory(), "aaa.txt");
try {
newxmlfile.createNewFile();
FileWriter fw = new FileWriter(newxmlfile);
fw.write("aaaaaaaaaaa");
//fw.close(); 我们在这里故意没有关闭 fw
} catch (IOException e) {
e.printStackTrace();
}
}
}
会产生如下异常信息:
... E/StrictMode(22056): A resource was acquired at attached stack trace but never released. See java.io.Closeable for information on avoiding resource leaks. ... E/StrictMode(22056): java.lang.Throwable: Explicit termination method 'close' not called ... E/StrictMode(22056): at dalvik.system.CloseGuard.open(CloseGuard.java:184) ... E/StrictMode(22056): at java.io.FileOutputStream.(FileOutputStream.java:90) ... E/StrictMode(22056): at java.io.FileOutputStream.(FileOutputStream.java:73) ... E/StrictMode(22056): at java.io.FileWriter.(FileWriter.java:42) ... E/StrictMode(22056): at com.ap.teststrictmode.MainActivityTestDetectLeakedClosableObjects.onCreate(MainActivityTestDetectLeakedClosableObjects.java:44) ... E/StrictMode(22056): at android.app.Activity.performCreate(Activity.java:5122) ... E/StrictMode(22056): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1081) ... E/StrictMode(22056): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270) ... E/StrictMode(22056): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2358) ... E/StrictMode(22056): at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3865) (后面的省略)
detectLeakedSqlLiteObjects() 和 detectLeakedClosableObjects()的用法类似,只不过是用来检查 SQLiteCursor 或者 其他 SQLite 对象是否被正确关闭。
- detectLeakedRegistrationObjects() 用来检查 BroadcastReceiver 或者 ServiceConnection 注册类对象是否被正确释放,看下面的代码
public class ActivityTestLeakedRegistrationObjects extends Activity {
private TextView textView = null;
private static boolean isStrictMode = false;
private MyReceiver receiver = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
this.textView = (TextView) findViewById(R.id.text_view);
this.textView.setText("In ActivityTestLeakedRegistrationObjects");
if(! isStrictMode){
StrictMode.setVmPolicy(new VmPolicy.Builder()
.detectLeakedRegistrationObjects()
.penaltyLog()
.build());
isStrictMode = true;
}
this.receiver = new MyReceiver();
IntentFilter filter = new IntentFilter();
filter.addAction("android.intent.action.MY_BROADCAST");
registerReceiver(this.receiver, filter);
}
@Override
protected void onDestroy() {
super.onDestroy();
}
}
输入信息如下:
...: E/ActivityThread(24442): Activity com.ap.teststrictmode.ActivityTestLeakedRegistrationObjects has leaked IntentReceiver com.ap.teststrictmode.MyReceiver@41f1f128 that was originally registered here. Are you missing a call to unregisterReceiver()? ...: E/ActivityThread(24442): android.app.IntentReceiverLeaked: Activity com.ap.teststrictmode.ActivityTestLeakedRegistrationObjects has leaked IntentReceiver com.ap.teststrictmode.MyReceiver@41f1f128 that was originally registered here. Are you missing a call to unregisterReceiver()? ...: E/ActivityThread(24442): at android.app.LoadedApk$ReceiverDispatcher.(LoadedApk.java:825) ...: E/ActivityThread(24442): at android.app.LoadedApk.getReceiverDispatcher(LoadedApk.java:596) ...: E/ActivityThread(24442): at android.app.ContextImpl.registerReceiverInternal(ContextImpl.java:1388) ...: E/ActivityThread(24442): at android.app.ContextImpl.registerReceiver(ContextImpl.java:1368) ...
正确做法应该是在 onDestroy() 方法中将 receiver 释放掉:
@Override
protected void onDestroy() {
unregisterReceiver(this.receiver);
super.onDestroy();
}
- setClassInstanceLimit(),设置某个类的同时处于内存中的实例上限,可以协助检查内存泄露。比如下面的代码:
public class ActivityTestObjectLimit extends Activity {
private static class MyClass{}
private static boolean isStrictMode = false;
private static List<MyClass> classList = new ArrayList<ActivityTestObjectLimit.MyClass>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(! isStrictMode){
StrictMode.setVmPolicy(new VmPolicy.Builder()
.setClassInstanceLimit(MyClass.class, 2)
.penaltyLog()
.build());
isStrictMode = true;
}
classList.add(new MyClass());
classList.add(new MyClass());
classList.add(new MyClass());
classList.add(new MyClass());
classList.add(new MyClass());
classList.add(new MyClass());
classList.add(new MyClass());
classList.add(new MyClass());
}
}
日志信息如下:
...: E/StrictMode(27681): class com.ap.teststrictmode.ActivityTestObjectLimit$MyClass; instances=72; limit=2 ...: E/StrictMode(27681): android.os.StrictMode$InstanceCountViolation: class com.ap.teststrictmode.ActivityTestObjectLimit$MyClass; instances=8; limit=2 ...: E/StrictMode(27681): at android.os.StrictMode.setClassInstanceLimit(StrictMode.java:1)
注意:上面的异常一般都在GC之后抛出,如果测试的时候没有现象,可以多翻转几次屏幕,或者通过DDMS工具手动触发一下。
发布者:全栈程序员-用户IM,转载请注明出处:https://javaforall.cn/132729.html原文链接:https://javaforall.cn
【正版授权,激活自己账号】: Jetbrains全家桶Ide使用,1年售后保障,每天仅需1毛
【官方授权 正版激活】: 官方授权 正版激活 支持Jetbrains家族下所有IDE 使用个人JB账号...