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Added in API level 9

StrictMode

public final class StrictMode
extends Object

java.lang.Object
   ↳ android.os.StrictMode


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 onCreate() method:

 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();
 }
 

You can decide what should happen when a violation is detected. For example, using 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. Future versions of Android may catch more (or fewer) operations, so you should never leave StrictMode enabled in applications distributed on Google Play.

Summary

Nested classes

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 StrictMode.ThreadPolicy from getThreadPolicy(), modifies it to permit disk reads, and sets the new policy with setThreadPolicy(StrictMode.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 StrictMode.ThreadPolicy from getThreadPolicy(), modifies it to permit both disk reads & writes, and sets the new policy with setThreadPolicy(StrictMode.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

Public methods

allowThreadDiskReads

Added in API level 9
StrictMode.ThreadPolicy allowThreadDiskReads ()

A convenience wrapper that takes the current StrictMode.ThreadPolicy from getThreadPolicy(), modifies it to permit disk reads, and sets the new policy with setThreadPolicy(StrictMode.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
StrictMode.ThreadPolicy allowThreadDiskWrites ()

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

enableDefaults

Added in API level 9
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(StrictMode.VmPolicy) and setThreadPolicy(StrictMode.ThreadPolicy).

getThreadPolicy

Added in API level 9
StrictMode.ThreadPolicy getThreadPolicy ()

Returns the current thread's policy.

Returns
StrictMode.ThreadPolicy

getVmPolicy

Added in API level 9
StrictMode.VmPolicy getVmPolicy ()

Gets the current VM policy.

Returns
StrictMode.VmPolicy

noteSlowCall

Added in API level 11
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 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
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
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
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