Added in API level 9

Summary: Nested Classes | Methods | Inherited Methods

StrictMode

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Kotlin |Java

public final class StrictMode
extends Object

java.lang.Object
↳	android.os.StrictMode

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StrictMode is a developer tool which detects things you might be doing by accident and brings them to your attention so you can fix them.

StrictMode is most commonly used to catch accidental disk or network access on the application's main thread, where UI operations are received and animations take place. Keeping disk and network operations off the main thread makes for much smoother, more responsive applications. By keeping your application's main thread responsive, you also prevent ANR dialogs from being shown to users.

Note that even though an Android device's disk is often on flash memory, many devices run a filesystem on top of that memory with very limited concurrency. It's often the case that almost all disk accesses are fast, but may in individual cases be dramatically slower when certain I/O is happening in the background from other processes. If possible, it's best to assume that such things are not fast.

Example code to enable from early in your Application, Activity, or other application component's Application.onCreate() method:

 public void onCreate() {
     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();
 }
 

You can decide what should happen when a violation is detected. For example, using StrictMode.ThreadPolicy.Builder.penaltyLog() you can watch the output of adb logcat while you use your application to see the violations as they happen.

If you find violations that you feel are problematic, there are a variety of tools to help solve them: threads, Handler, AsyncTask, IntentService, etc. But don't feel compelled to fix everything that StrictMode finds. In particular, many cases of disk access are often necessary during the normal activity lifecycle. Use StrictMode to find things you did by accident. Network requests on the UI thread are almost always a problem, though.

StrictMode is not a security mechanism and is not guaranteed to find all disk or network accesses. While it does propagate its state across process boundaries when doing Binder calls, it's still ultimately a best effort mechanism. Notably, disk or network access from JNI calls won't necessarily trigger it.

Summary

Nested classes
interface	StrictMode.OnThreadViolationListener When #StrictMode.ThreadPolicy.Builder.penaltyListener(Executor, OnThreadViolationListener) is enabled, the listener is called on the provided executor when a Thread violation occurs.
interface	StrictMode.OnVmViolationListener When #StrictMode.VmPolicy.Builder.penaltyListener(Executor, OnVmViolationListener) is enabled, the listener is called on the provided executor when a VM violation occurs.
class	StrictMode.ThreadPolicy StrictMode policy applied to a certain thread.
class	StrictMode.VmPolicy StrictMode policy applied to all threads in the virtual machine's process.

Public methods
static StrictMode.ThreadPolicy	allowThreadDiskReads() A convenience wrapper that takes the current ThreadPolicy from getThreadPolicy(), modifies it to permit disk reads, and sets the new policy with setThreadPolicy(ThreadPolicy), returning the old policy so you can restore it at the end of a block.
static StrictMode.ThreadPolicy	allowThreadDiskWrites() A convenience wrapper that takes the current ThreadPolicy from getThreadPolicy(), modifies it to permit both disk reads & writes, and sets the new policy with setThreadPolicy(ThreadPolicy), returning the old policy so you can restore it at the end of a block.
static void	enableDefaults() Enable the recommended StrictMode defaults, with violations just being logged.
static StrictMode.ThreadPolicy	getThreadPolicy() Returns the current thread's policy.
static StrictMode.VmPolicy	getVmPolicy() Gets the current VM policy.
static void	noteSlowCall(String name) For code to note that it's slow.
static void	setThreadPolicy(StrictMode.ThreadPolicy policy) Sets the policy for what actions on the current thread should be detected, as well as the penalty if such actions occur.
static void	setVmPolicy(StrictMode.VmPolicy policy) Sets the policy for what actions in the VM process (on any thread) should be detected, as well as the penalty if such actions occur.

Inherited methods

From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long timeoutMillis, int nanos) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait(long timeoutMillis) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait() Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Public methods

allowThreadDiskReads

Added in API level 9

public static StrictMode.ThreadPolicy allowThreadDiskReads ()

A convenience wrapper that takes the current ThreadPolicy from getThreadPolicy(), modifies it to permit disk reads, and sets the new policy with setThreadPolicy(ThreadPolicy), returning the old policy so you can restore it at the end of a block.

Returns
StrictMode.ThreadPolicy	the old policy, to be passed to setThreadPolicy to restore the policy.

allowThreadDiskWrites

Added in API level 9

public static StrictMode.ThreadPolicy allowThreadDiskWrites ()

A convenience wrapper that takes the current ThreadPolicy from getThreadPolicy(), modifies it to permit both disk reads & writes, and sets the new policy with setThreadPolicy(ThreadPolicy), returning the old policy so you can restore it at the end of a block.

Returns
StrictMode.ThreadPolicy	the old policy, to be passed to setThreadPolicy(ThreadPolicy) to restore the policy at the end of a block

enableDefaults

Added in API level 9

public static void enableDefaults ()

Enable the recommended StrictMode defaults, with violations just being logged.

This catches disk and network access on the main thread, as well as leaked SQLite cursors and unclosed resources. This is simply a wrapper around setVmPolicy(VmPolicy) and setThreadPolicy(ThreadPolicy).

getThreadPolicy

Added in API level 9

public static StrictMode.ThreadPolicy getThreadPolicy ()

Returns the current thread's policy.

Returns
StrictMode.ThreadPolicy

getVmPolicy

Added in API level 9

public static StrictMode.VmPolicy getVmPolicy ()

Gets the current VM policy.

Returns
StrictMode.VmPolicy

noteSlowCall

Added in API level 11

public static void noteSlowCall (String name)

For code to note that it's slow. This is a no-op unless the current thread's StrictMode.ThreadPolicy has StrictMode.ThreadPolicy.Builder.detectCustomSlowCalls() enabled.

Parameters
name	String: a short string for the exception stack trace that's built if when this fires.

setThreadPolicy

Added in API level 9

public static void setThreadPolicy (StrictMode.ThreadPolicy policy)

Sets the policy for what actions on the current thread should be detected, as well as the penalty if such actions occur.

Internally this sets a thread-local variable which is propagated across cross-process IPC calls, meaning you can catch violations when a system service or another process accesses the disk or network on your behalf.

Parameters
policy	StrictMode.ThreadPolicy: the policy to put into place

setVmPolicy

Added in API level 9

public static void setVmPolicy (StrictMode.VmPolicy policy)

Sets the policy for what actions in the VM process (on any thread) should be detected, as well as the penalty if such actions occur.

Parameters
policy	StrictMode.VmPolicy: the policy to put into place