在flatMap中出现NetworkOnMainThreadException异常

Question

在flatMap中出现NetworkOnMainThreadException异常

5

我刚开始接触rxjava或者rxandroid，并且想要用observable和subscriber来改善我的AsyncTask和回调地狱。但是我遇到了一个问题：我需要向我的数据库发起两个请求。

第一个请求的响应将会成为第二个请求的结果。我尝试使用flatMap来解决这个问题。第一个请求的返回值没问题，但是第二个请求却报错：NetworkOnMainThreadException。

我知道请求是在主线程上执行的，但是为什么呢？我尝试在flatMap之前添加subscribeOn(Schedulers.io())，但结果还是一样。您能帮助我解决这个问题并解释我做错了什么吗？非常感谢。下面是我的代码......

private void getFavouriteList(){
    Observable.create((Observable.OnSubscribe<PaginatedScanList<UserDO>>) subscriber -> {
        final Map<String, AttributeValue> filterExpressionAttributeValues = new HashMap<>();
        filterExpressionAttributeValues
                .put(":val1", new AttributeValue().withS(sharedPreferences.getString("socialId", "")));
        final DynamoDBScanExpression scanExpression = new DynamoDBScanExpression()
                .withFilterExpression("socialId = :val1")
                .withExpressionAttributeValues(filterExpressionAttributeValues);
        PaginatedScanList<UserDO> result = dynamoDBMapper.scan(UserDO.class, scanExpression);
        Log.d(TAG, "first result size " + result.size());
        subscriber.onNext(result);
        subscriber.onCompleted();
    })
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .filter(result -> {
                if(result.isEmpty()) {
                    Toast.makeText(context, "Can not find user", Toast.LENGTH_SHORT).show();
                    return false;
                }
                return true;
            })
            .flatMap(user -> Observable.from(user.get(0).getFavourites()))
            .subscribeOn(Schedulers.io())
            .flatMap(result -> {
                final Map<String, AttributeValue> filterExpressionAttributeValues = new HashMap<>();
                filterExpressionAttributeValues
                        .put(":val1", new AttributeValue().withS(result));
                filterExpressionAttributeValues
                        .put(":val2", new AttributeValue().withN("1"));
                final DynamoDBScanExpression scanExpression = new DynamoDBScanExpression()
                        .withFilterExpression("productId = :val1 and selling = :val2")
                        .withExpressionAttributeValues(filterExpressionAttributeValues);
                PaginatedScanList<ProductDO> res = dynamoDBMapper.scan(ProductDO.class, scanExpression);
                Log.d(TAG, "second result size " + res.size());
                return Observable.from(res);
            })
            .subscribe(new Subscriber<ProductDO>() {
                @Override
                public void onCompleted() {
                    favouriteProgressBar.setVisibility(View.INVISIBLE);
                }

                @Override
                public void onError(Throwable e) {
                    e.printStackTrace();
                    favouriteProgressBar.setVisibility(View.INVISIBLE);
                }

                @Override
                public void onNext(ProductDO productDO) {
                    Log.d(TAG, "productId " + productDO.getProductId());
                    product.add(productDO);
                    adapter.notifyDataSetChanged();
                }
            });
}

- Alex Khotiun

https://dev59.com/-mw15IYBdhLWcg3w3vpe - Konstantin Pribluda

1个回答

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- JohnWowUs · Accepted Answer

将.observeOn（AndroidSchedulers.mainThread()）移动到您的subscribe之前。

附：除非没有其他选择，否则不应使用Observable.create()。

编辑以修复过滤器中的Toast问题。

private void getFavouriteList(){
    Observable.create((Observable.OnSubscribe<PaginatedScanList<UserDO>>) subscriber -> {
        final Map<String, AttributeValue> filterExpressionAttributeValues = new HashMap<>();
        filterExpressionAttributeValues
                .put(":val1", new AttributeValue().withS(sharedPreferences.getString("socialId", "")));
        final DynamoDBScanExpression scanExpression = new DynamoDBScanExpression()
                .withFilterExpression("socialId = :val1")
                .withExpressionAttributeValues(filterExpressionAttributeValues);
        PaginatedScanList<UserDO> result = dynamoDBMapper.scan(UserDO.class, scanExpression);
        Log.d(TAG, "first result size " + result.size());
        subscriber.onNext(result);
        subscriber.onCompleted();
    })
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .filter(result -> {
                if(result.isEmpty()) {
                    Toast.makeText(context, "Can not find user", Toast.LENGTH_SHORT).show();
                    return false;
                }
                return true;
            })
            .observeOn(Schedulers.io())
            .flatMap(user -> Observable.from(user.get(0).getFavourites()))
            .flatMap(result -> {
                final Map<String, AttributeValue> filterExpressionAttributeValues = new HashMap<>();
                filterExpressionAttributeValues
                        .put(":val1", new AttributeValue().withS(result));
                filterExpressionAttributeValues
                        .put(":val2", new AttributeValue().withN("1"));
                final DynamoDBScanExpression scanExpression = new DynamoDBScanExpression()
                        .withFilterExpression("productId = :val1 and selling = :val2")
                        .withExpressionAttributeValues(filterExpressionAttributeValues);
                PaginatedScanList<ProductDO> res = dynamoDBMapper.scan(ProductDO.class, scanExpression);
                Log.d(TAG, "second result size " + res.size());
                return Observable.from(res);
            })
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(new Subscriber<ProductDO>() {
                @Override
                public void onCompleted() {
                    favouriteProgressBar.setVisibility(View.INVISIBLE);
                }

                @Override
                public void onError(Throwable e) {
                    e.printStackTrace();
                    favouriteProgressBar.setVisibility(View.INVISIBLE);
                }

                @Override
                public void onNext(ProductDO productDO) {
                    Log.d(TAG, "productId " + productDO.getProductId());
                    product.add(productDO);
                    adapter.notifyDataSetChanged();
                }
            });
}