RxJava创建倒计时器

客官°小女子只卖身不卖艺 2022-12-23 06:14 225阅读 0赞

用RxJava创建一个倒计时计时器，感觉是一个很简单的事情，用intervalRange操作符就可以搞定了。但是我的场景是，需要点击Button（重新获取数据）去进行网络请求，将请求的结果进行UI显示，并进行倒计时计算。网络请求的返回体如下所示：

public class Response {
        private String data;	// 网络请求的数据
        private long countDownSeconds;		// 剩余的时间数，单位 s
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1plbmdUdWRvdQ_size_16_color_FFFFFF_t_70_pic_center]  
我的初步实现如下（MainActivity.java）：

public class MainActivity extends AppCompatActivity {
        private static final String TAG = "MainActivity";
        private Disposable disposable;
        private TextView countDownMsgTv, dataTv;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            Button button = findViewById(R.id.bt_click);
            countDownMsgTv = findViewById(R.id.tv_count_down);
            dataTv = findViewById(R.id.tv_data);
            button.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                   Observable.just(getResponse())   // mock网络请求
                           .subscribeOn(Schedulers.io())
                           .observeOn(AndroidSchedulers.mainThread())
                           .subscribe(new Consumer<Response>() {
                               @Override
                               public void accept(Response response) throws Exception {
                                   dataTv.setText(response.getData());
    
                                   // 计时器
                                   countDown(response.getCountDownSeconds());
                               }
                           });
                }
            });
    
        }
        // 使用RxJava来构建计时器
        private void countDown(final long countDownSeconds){
            Observable.intervalRange(0, countDownSeconds, 0, 1, TimeUnit.SECONDS)
                    .map(new Function<Long, Long>() {
                        @Override
                        public Long apply(Long aLong) throws Exception {
                            return countDownSeconds -aLong;
                        }
                    })
                    .subscribeOn(Schedulers.io())
                    .observeOn(AndroidSchedulers.mainThread())
                    .subscribe(new Observer<Long>() {
                        @Override
                        public void onSubscribe(Disposable d) {
                            Log.i(TAG, "onSubscribe: ");
                        }
    
                        @Override
                        public void onNext(Long value) {
                            countDownMsgTv.setText(getCountDownMsg(String.valueOf(value)));
                            Log.i(TAG, "还剩" +  value + "s");
                        }
    
                        @Override
                        public void onError(Throwable e) {
                            Log.i(TAG, "onError: ");
                        }
    
                        @Override
                        public void onComplete() {
                            Log.i(TAG, "onComplete: ");
                        }
                    });
        }
    
        /**
         * Mock网络请求的返回
         */
        private Response getResponse(){
            Response resp = new Response();
            resp.setCountDownSeconds(30);
            resp.setData("你好");
            return resp;
        }
    }

点击了Button之后，发现基本能实现功能：

2020-11-22 21:29:54.594 I/MainActivity: onSubscribe: 
    2020-11-22 21:29:54.608 I/MainActivity: 还剩30s
    2020-11-22 21:29:55.599 I/MainActivity: 还剩29s
    2020-11-22 21:29:56.599 I/MainActivity: 还剩28s
    ... 
    2020-11-22 21:30:21.600 I/MainActivity: 还剩3s
    2020-11-22 21:30:22.600 I/MainActivity: 还剩2s
    2020-11-22 21:30:23.599 I/MainActivity: 还剩1s
    2020-11-22 21:30:23.600 I/MainActivity: onComplete:

存在一个问题，当上一次计时尚未结束时，又点击了Button，发现会有多个计时器在运行

2020-11-22 21:32:31.543 18130-18130 I/MainActivity: onSubscribe: 
    2020-11-22 21:32:31.556 18130-18130 I/MainActivity: 还剩30s
    2020-11-22 21:32:32.558 18130-18130 I/MainActivity: onSubscribe: // 二次点击
    2020-11-22 21:32:32.559 18130-18130 I/MainActivity: 还剩29s
    2020-11-22 21:32:32.573 18130-18130 I/MainActivity: 还剩30s
    2020-11-22 21:32:33.546 18130-18130 I/MainActivity: 还剩28s
    2020-11-22 21:32:33.561 18130-18130 I/MainActivity: 还剩29s
    2020-11-22 21:32:34.546 18130-18130 I/MainActivity: 还剩27s
    2020-11-22 21:32:34.561 18130-18130 I/MainActivity: 还剩28s
    ...
    2020-11-22 21:32:58.560 18130-18130 I/MainActivity: 还剩4s
    2020-11-22 21:32:59.546 18130-18130 I/MainActivity: 还剩2s
    2020-11-22 21:32:59.561 18130-18130 I/MainActivity: 还剩3s
    2020-11-22 21:33:00.547 18130-18130 I/MainActivity: 还剩1s
    2020-11-22 21:33:00.548 18130-18130 I/MainActivity: onComplete: 
    2020-11-22 21:33:00.561 18130-18130 I/MainActivity: 还剩2s
    2020-11-22 21:33:01.561 18130-18130 I/MainActivity: 还剩1s
    2020-11-22 21:33:01.562 18130-18130 I/MainActivity: onComplete:

导致上述结果的原因是，上一个计时器还没有被Dispose，下一个计时器又重新开始了，这样会导致有多个计时器在运行。在创建计时器时，先检查之前的计时器是否还存在，如果存在，则dispose掉。

private void countDown(final long countDownSeconds){
            if(disposable != null && !disposable.isDisposed()){	// 在创建计时器时，先检查之前的计时器是否还存在，如果存在，则dispose掉。
                disposable.dispose();
            }
            Observable.intervalRange(0, countDownSeconds, 0, 1, TimeUnit.SECONDS)
                    .map(new Function<Long, Long>() {
                        @Override
                        public Long apply(Long aLong) throws Exception {
                            return countDownSeconds -aLong;
                        }
                    })
                    .subscribeOn(Schedulers.io())
                    .observeOn(AndroidSchedulers.mainThread())
                    .subscribe(new Observer<Long>() {
                        @Override
                        public void onSubscribe(Disposable d) {
                            disposable = d;	// 区别！！！
                            Log.i(TAG, "onSubscribe: ");
                        }
    
                        @Override
                        public void onNext(Long value) {
                            countDownMsgTv.setText(getCountDownMsg(String.valueOf(value)));
                            Log.i(TAG, "还剩" +  value + "s");
                        }
    
                        @Override
                        public void onError(Throwable e) {
                            Log.i(TAG, "onError: ");
                        }
    
                        @Override
                        public void onComplete() {
                            Log.i(TAG, "onComplete: ");
                        }
                    });
        }

重新运行后结果如下：

2020-11-22 21:40:14.911 18283-18283 I/MainActivity: onSubscribe: 
    2020-11-22 21:40:14.927 18283-18283 I/MainActivity: 还剩30s
    2020-11-22 21:40:15.918 18283-18283 I/MainActivity: 还剩29s
    2020-11-22 21:40:16.917 18283-18283 I/MainActivity: 还剩28s
    2020-11-22 21:40:19.228 18283-18283 I/MainActivity: onSubscribe: // 二次点击
    2020-11-22 21:40:19.245 18283-18283 I/MainActivity: 还剩30s
    2020-11-22 21:40:20.232 18283-18283 I/MainActivity: 还剩29s
    2020-11-22 21:40:21.231 18283-18283 I/MainActivity: 还剩28s
    2020-11-22 21:40:22.231 18283-18283 I/MainActivity: 还剩27s
    ... 
    2020-11-22 21:40:47.231 18283-18283 I/MainActivity: 还剩2s
    2020-11-22 21:40:48.231 18283-18283 I/MainActivity: 还剩1s
    2020-11-22 21:40:48.231 18283-18283 I/MainActivity: onComplete:

这样写，有两层的RxJava进行嵌套，代码阅读体验上不够优美。可以用一个flatMap操作符来将请求的结果作一次转换，并在doOnNext时显示数据，另外还需要注意线程切换的问题。

public class MainActivity extends AppCompatActivity {
        private static final String TAG = "MainActivity";
        private Disposable disposable;
        private TextView countDownMsgTv, dataTv;
        private long countDownSeconds;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            Button button = findViewById(R.id.bt_click);
            countDownMsgTv = findViewById(R.id.tv_count_down);
            dataTv = findViewById(R.id.tv_data);
            button.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if(disposable != null && !disposable.isDisposed()){
                        disposable.dispose();
                    }
                    Observable.just(getResponse())   // mock网络请求
                            .subscribeOn(Schedulers.io())               // 把前面的 切换到io线程执行
                            .observeOn(AndroidSchedulers.mainThread())  // 把后面的 切换到主线程执行
                            .doOnNext(new Consumer<Response>() {	// 显示数据
                               @Override
                               public void accept(Response response) throws Exception {
                                   Log.i(TAG, "set data");
                                   dataTv.setText(response.getData());
                               }
                            })
                            .observeOn(Schedulers.io())                 // 把后面的 切换到io线程执行
                            .flatMap(new Function<Response, ObservableSource<Long>>() {
                               @Override
                               public ObservableSource<Long> apply(Response response) throws Exception {
                                   countDownSeconds = response.getCountDownSeconds();
                                   return Observable.intervalRange(0, countDownSeconds, 0, 1,TimeUnit.SECONDS);
                               }
                           })
                            .map(new Function<Long, Long>() {
                                @Override
                                public Long apply(Long aLong) throws Exception {
                                    return countDownSeconds - aLong;
                                }
                            })
                            .observeOn(AndroidSchedulers.mainThread())  // 把后面的 切换到主线程执行
                            .subscribe(new Observer<Long>() {
                            @Override
                            public void onSubscribe(Disposable d) {
                                disposable = d;
                                Log.i(TAG, "onSubscribe: ");
                            }
    
                            @Override
                            public void onNext(Long value) {
                                countDownMsgTv.setText(getCountDownMsg(String.valueOf(value)));
                                Log.i(TAG, "还剩" +  value + "s");
                            }
    
                            @Override
                            public void onError(Throwable e) {
                                Log.i(TAG, "onError: ");
                            }
    
                            @Override
                            public void onComplete() {
                                Log.i(TAG, "onComplete: ");
                            }
                        });
                }
            });
    
        }
    
    
        private String getCountDownMsg(String s){
            return String.format("还剩余: %s s", s);
        }
        @Override
        protected void onDestroy() {	// 在activity销毁时需要dispose掉，否则会导致内存泄漏
            super.onDestroy();
            if(disposable != null && !disposable.isDisposed()){
                disposable.dispose();
            }
        }
    
        /**
         * Mock网络请求的返回
         */
        private Response getResponse(){
            Response resp = new Response();
            resp.setCountDownSeconds(30);
            resp.setData("你好");
            return resp;
        }
    }

运行结果如下，符合预期，并且代码更优美了。

2020-11-22 21:58:14.091 18661-18661 I/MainActivity: onSubscribe: 
    2020-11-22 21:58:14.108 18661-18661 I/MainActivity: set data
    2020-11-22 21:58:14.125 18661-18661 I/MainActivity: 还剩30s
    2020-11-22 21:58:15.114 18661-18661 I/MainActivity: 还剩29s
    .. 
    2020-11-22 21:58:30.816 18661-18661 I/MainActivity: onSubscribe: // 二次点击
    2020-11-22 21:58:30.823 18661-18661 I/MainActivity: set data
    2020-11-22 21:58:30.844 18661-18661 I/MainActivity: 还剩30s
    2020-11-22 21:58:31.826 18661-18661 I/MainActivity: 还剩29s
    ...
    2020-11-22 21:58:58.827 18661-18661 I/MainActivity: 还剩2s
    2020-11-22 21:58:59.827 18661-18661 I/MainActivity: 还剩1s
    2020-11-22 21:58:59.827 18661-18661 I/MainActivity: onComplete:

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