Day: November 21, 2017

There is a crash that is showing up repeatedly in Firebase crash reporting for my React Native Android app. However, I am at a loss as to what would be causing it, as the stack trace doesn’t cite any of my code. Does anyone know what might be the cause? I am on React Native 0.47.1

The stack trace is as follows:

Exception java.lang.RuntimeException: java.lang.InterruptedException
com.facebook.react.common.futures.SimpleSettableFuture.getOrThrow (SimpleSettableFuture.java:102)
com.facebook.react.bridge.queue.MessageQueueThreadImpl.startNewBackgroundThread (MessageQueueThreadImpl.java:199)
com.facebook.react.bridge.queue.MessageQueueThreadImpl.create (MessageQueueThreadImpl.java:146)
com.facebook.react.bridge.queue.ReactQueueConfigurationImpl.create (ReactQueueConfigurationImpl.java:87)
com.facebook.react.bridge.CatalystInstanceImpl.<init> (CatalystInstanceImpl.java:101)
com.facebook.react.bridge.CatalystInstanceImpl.<init> (CatalystInstanceImpl.java:42)
com.facebook.react.bridge.CatalystInstanceImpl$Builder.build (CatalystInstanceImpl.java:574)
com.facebook.react.ReactInstanceManager.createReactContext (ReactInstanceManager.java:999)
com.facebook.react.ReactInstanceManager.access$600 (ReactInstanceManager.java:109)
com.facebook.react.ReactInstanceManager$4.run (ReactInstanceManager.java:802)
java.lang.Thread.run (Thread.java:761)

Caused by java.lang.InterruptedException:
java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly (AbstractQueuedSynchronizer.java:1301)
java.util.concurrent.CountDownLatch.await (CountDownLatch.java:203)
com.facebook.react.common.futures.SimpleSettableFuture.get (SimpleSettableFuture.java:66)
com.facebook.react.common.futures.SimpleSettableFuture.getOrThrow (SimpleSettableFuture.java:100)
com.facebook.react.bridge.queue.MessageQueueThreadImpl.startNewBackgroundThread (MessageQueueThreadImpl.java:199)
com.facebook.react.bridge.queue.MessageQueueThreadImpl.create (MessageQueueThreadImpl.java:146)
com.facebook.react.bridge.queue.ReactQueueConfigurationImpl.create (ReactQueueConfigurationImpl.java:87)
com.facebook.react.bridge.CatalystInstanceImpl.<init> (CatalystInstanceImpl.java:101)
com.facebook.react.bridge.CatalystInstanceImpl.<init> (CatalystInstanceImpl.java:42)
com.facebook.react.bridge.CatalystInstanceImpl$Builder.build (CatalystInstanceImpl.java:574)
com.facebook.react.ReactInstanceManager.createReactContext (ReactInstanceManager.java:999)
com.facebook.react.ReactInstanceManager.access$600 (ReactInstanceManager.java:109)
com.facebook.react.ReactInstanceManager$4.run (ReactInstanceManager.java:802)
java.lang.Thread.run (Thread.java:761)

Answer

This problem also occur for many others as well and the cause is various. You can find the discussion about it here. Since I really don’t know what your app does so here is some possible reasons:

1. You’re using react-native-navigation (you can try change it back to react-navigation)
2. You’re using react-native-image-crop-picker or react-native-image-picker (Which produce the same error that make your app crash on some device and it throw InterruptedException

If the problem is number 2 you can try to fix it by alter MainApplication.java:

@Override
public boolean clearHostOnActivityDestroy() {
    return false;
}

The fix in number 2 was also reference from here under acintyo answer.

As for changing the react-native version you can try it but I do not recommend it since after reading through the issues mentioned above, I saw that many version also experienced this issues (most of them are 0.49.+ or 0.45.x)

I have a LiveData object that depends on another LiveData. As I understand, Transformations.switchMap should allow to chain them. But switchMap handler is triggered only once and it doesn’t react on further updates. If instead I use observe on the first object and, when it’s ready, retrieve the second, it works fine but in this case I have to do it in Activity rather than ViewModel. Is it possible to chain LiveData objects, like Transformations.switchMap, but receive all updates, not only the first one?

Here is an attempt to use switchMap:

LiveData<Resource<User>> userLiveData = usersRepository.get();
return Transformations.switchMap(userLiveData, resource -> {
    if (resource.status == Status.SUCCESS && resource.data != null) {
        return apiService.cartItems("Bearer " + resource.data.token);
    } else {
        return AbsentLiveData.create();
    }
});

Here is an approach with observe in activity (works but requires to keep logic in activity):

viewModel.user().observe(this, x -> {
    if (x != null && x.data != null) {
        viewModel.items(x.data.token).observe(this, result -> {
            // use result
        });
    }
});

Answer

As a workaround, I used MediatorLiveData. I add the result of the first call as a source and, when it’s ready, replace it with a final call:

MediatorLiveData<MyResponse> result = new MediatorLiveData<>();
LiveData<Resource<User>> source = this.get();
result.addSource(source, resource -> {
    if (resource.status == Status.SUCCESS && resource.data != null) {
        result.removeSource(source);
        result.addSource(apiService.cartItems("Bearer " + resource.data.token), result::postValue);
    }
});
return result;

I disabled the intellij dialog asking for converting Java code to Kotlin code on copy paste code from Java to Kotlin thinking that it would always convert without asking, but now it never converts. How can I enable this dialog again? I couldn’t find any way to do it and now the IDE is not converting Java to Kotlin on copy + paste anymore.

Answer

Open preferences (Windows = Ctrl-Alt-S, Mac = Cmd-,).

Go to Editor -> General -> Smart Keys and scroll to the bottom.

The Convert pasted Java code to Kotlin and Don't show Java to Kotlin conversion dialog during paste options should be in the Kotlin section

Why does Kotlin not have a LinkedList implementation in the Kotlin Standard Library (stdlib)?

If I’m working with Kotlin in the JVM I’m using the Java LinkedList source.

Is there an equivalent in the stdlib (in particular regarding Kotlin Native Development)?

Answer

Kotlin does not have its own collections because it would be too difficult to maintain Java interoperability. Instead, the Kotlin Standard Library just adds some extension functions to the Java collections to make them easier to work with.

To quote Kotlin in Action:

Why are there no Kotlin collections? Because using the standard Java collections makes it much easier to interact with Java code. You don’t need to convert collections one way or the other when you call Java functions from Kotlin or vice versa.

I am trying to declare a variable in a react-js class. The variable should be accessible in different functions. This is my code

class MyContainer extends Component {
    constructor(props) {
        super(props);
        this.testVariable= "this is a test";  // I declare the variable here
    }
    onMove() {
        console.log(this.testVariable); //I try to access it here
    }
}

On onMove, the value of this.testVariable is undefined. I Know that I could put the value on the state but I don’t want to do it because each time the value changes, render() will be called which is not necessary. I am new to react, did I make something wrong?

Answer

Using ES6 syntax in React does not bind this to user-defined functions however it will bind this to the component lifecycle methods.

So the function that you declared will not have the same context as the class and trying to access this will not give you what you are expecting.

For getting the context of class you have to bind the context of class to the function or use arrow functions.

Method 1 to bind the context:

class MyContainer extends Component {

    constructor(props) {
        super(props);
        this.onMove = this.onMove.bind(this);
        this.testVarible= "this is a test";
    }

    onMove() {
        console.log(this.testVarible);
    }
}

Method 2 to bind the context:

class MyContainer extends Component {

    constructor(props) {
        super(props);
        this.testVarible= "this is a test";
    }

    onMove = () => {
        console.log(this.testVarible);
    }
}

Method 2 is my preferred way but you are free to choose your own.

Update: You can also create the properties on class without constructor:

class MyContainer extends Component {

    testVarible= "this is a test";

    onMove = () => {
        console.log(this.testVarible);
    }
}

Note If you want to update the view as well, you should use state and setState method when you set or change the value.

Example:

class MyContainer extends Component {

    state = { testVarible: "this is a test" };

    onMove = () => {
        console.log(this.state.testVarible);
        this.setState({ testVarible: "new value" });
    }
}