Android rxjava - 技术栈

一.简介

RxJava是ReactiveX在JVM上的一个实现，ReactiveX使用Observable序列组合异步和基于事件的程序的库；是一个基于事件流、实现异步操作的库。RxJava在Java环境下使用，它通过Observable（可观测对象）和Subscriber（订阅者）来实现异步编程模型。Observable可以发射出一系列的数据流，而Subscriber则负责处理这些数据流。利用各种操作符，我们可以对数据流进行变换、过滤、合并等操作，从而完成复杂的异步任务。

rx == 反应式 reactivex == 响应式编程：根据上一层的响应影响下一层的变化

Observable被观察者理解为起点，Observer观察者理解为终点，通过Subscribe连接两者

二、简单使用

1.bulid.gradle

java 复制代码

implementation 'io.reactivex.rxjava3:rxandroid:3.0.2'
// Because RxAndroid releases are few and far between, it is recommended you also
// explicitly depend on RxJava's latest version for bug fixes and new features.
// (see https://github.com/ReactiveX/RxJava/releases for latest 3.x.x version)
implementation 'io.reactivex.rxjava3:rxjava:3.1.5'

2.使用rxjava下载网络图片

java 复制代码

// 网络图片的链接地址
    private final static String PATH = "https://pixiv.re/103070121.jpg";

public void showImage() {
        //第二步
        //起点
        Observable.just(PATH)
                //第三步
                //图片下载需求
                .map(new Function<String, Bitmap>() {
                    @Override
                    public Bitmap apply(String path) throws Throwable {
                        try {

                            Thread.sleep(2000);
                            URL url = new URL(path);
                            //建立网络连接对象
                            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
                            httpURLConnection.setConnectTimeout(5000);
                            int response = httpURLConnection.getResponseCode();
                            if (response == HttpURLConnection.HTTP_OK) {
                                InputStream inputStream = httpURLConnection.getInputStream();
                                Bitmap bitmap = BitmapFactory.decodeStream(inputStream);

                                return bitmap;
                            }
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                        return null;
                    }
                })
                // 加水印
                .map(new Function<Bitmap, Bitmap>() {
                    @Override
                    public Bitmap apply(Bitmap bitmap) throws Throwable {
                        Paint paint = new Paint();
                        paint.setColor(Color.RED);
                        paint.setTextSize(10);
                        Bitmap syBitmap = drawTextToBitmap(bitmap,"pixiv",paint,50,10);
                        return syBitmap;
                    }
                })

                // 日志记录需求
                .map(new Function<Bitmap, Bitmap>() {
                    @NonNull
                    @Override
                    public Bitmap apply(@NonNull Bitmap bitmap) throws Exception {
                        Log.e("TAG", "什么时候下载了图片 apply: " + System.currentTimeMillis());
                        return bitmap;
                    }
                })

                //图片下载操作分配异步线程
                .subscribeOn(Schedulers.io())
                //终点分配Android主线程
                .observeOn(AndroidSchedulers.mainThread())
                
                .subscribe(
                    //终点
                    new Observer<Bitmap>() {
                    //第一步
                    //订阅成功
                    @Override
                    public void onSubscribe(@NonNull Disposable d) {
                        layout.setVisibility(View.VISIBLE);
                    }
                    
                    //第四步 显示图片
                    @Override
                    public void onNext(@NonNull Bitmap bitmap) {
                        image.setImageBitmap(bitmap);
                    }

                    //异常
                    @Override
                    public void onError(@NonNull Throwable e) {

                    }
                    
                    //第五步 结束
                    @Override
                    public void onComplete() {
                        if (progressDialog != null) {
                            layout.setVisibility(View.GONE);
                        }
                    }
                });
    }

个人理解太浅，详细使用请参考：

Rxjava3文档级教程一：介绍和基本使用-CSDN博客

How To Use RxJava · ReactiveX/RxJava Wiki (github.com)

ReactiveX/RxJava: RxJava -- Reactive Extensions for the JVM -- a library for composing asynchronous and event-based programs using observable sequences for the Java VM. (github.com)

Observer (RxJava Javadoc 3.1.8) (reactivex.io)