Created
July 10, 2012 15:52
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Properly test async Android code
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/* | |
I've been writing tests for Android code that uses Handlers to communicate with background threads. | |
I couldn't get my callbacks to be called back to. | |
I got angry. | |
I finally found the solution...after way too much looking. | |
Here it is. | |
*/ | |
package com.caseycrites.android.testexample | |
import java.util.concurrent.CountDownLatch; | |
import junit.framework.Assert; | |
import android.os.Handler; | |
import android.os.Looper; | |
import android.os.Message; | |
import android.test.InstrumentationTestCase; | |
import com.caseycrites.android.SomeClass; | |
/* | |
Make sure you extend InstrumentationTestCase. | |
Maybe that's not true, you can mess around with it, let me know if others work. | |
*/ | |
public class AsyncTest extends InstrumentationTestCase { | |
int what = -1; | |
Object obj; | |
CountDownLatch latch; | |
SomeClass someClass; | |
@Override | |
public void setUp() throws Exception { | |
super.setUp(); | |
this.someClass = new SomeClass(); | |
} | |
@Override | |
public void tearDown() throws Exception { | |
super.tearDown(); | |
this.what = -1; | |
this.obj = null; | |
} | |
public void testHandlerCode() { | |
this.latch = new CountDownLatch(1); | |
new LooperThread() { | |
@Override | |
public void run() { | |
AsyncTest.this.someClass.someMethod(new Handler() { | |
@Override | |
public void handleMessage(Message message) { | |
AsyncTest.this.what = message.what; | |
AsyncTest.this.obj = message.obj; | |
AsyncTest.this.latch.countDown(); | |
} | |
}); | |
} | |
}.start(); | |
this.latch.await(); | |
Assert.assertNotEquals(-1, this.what); | |
Assert.assertNotNull(this.obj); | |
} | |
static class LooperThread extends Thread { | |
@Override | |
public void start() { | |
new Thread() { | |
@Override | |
public void run() { | |
Looper.prepare(); | |
LooperThread.this.run(); | |
Looper.run(); | |
} | |
}.start(); | |
} | |
} | |
} | |
/* | |
Note: This should also work fine for testing AsyncTasks. | |
What I don't get and maybe someone can explain it to me, is why can't I send messages to my handler without creating a new Thread with a Looper? | |
InstrumentationTestCase (and most other Android supplied TestCases...I think?) have their own Looper? So why can't I send it messages? | |
Perhaps the Looper's message queue is reserved for the Android TestRunner's use only? | |
*/ |
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