StrictMode 详解

发表于 2014-04-24 23:44:45

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()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;

    @Override protected 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。