项目里需要App端不断地从服务器获取数据，实时生成图表。图表控件使用的是MPAndroidChart。自己写了些实时更新折线图的demo，数据是线程随机生成的，不是后台数据。
1、Message配合Handler实现
效果如下
Message配合Handler实现.gif
在MainActivity中创建一个产生随机数据的线程，每产生一个数据发送一个Message，Handler收到Message之后更新折线图。
MainActivity代码如下：
public class MainActivity extends AppCompatActivity {
private static final int TAG = 1;//Message的what标识
private TextView mTextView;
private Button mStartButton;
private LineChart mLineChart;
private Data[] mDatas;
private List mEntries = new ArrayList<>();
private Thread mThread;
private Handler mHandler;
private Random mRandom;
private StringBuilder mStringBuilder;
private int mEndIndex;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mTextView = findViewById(R.id.test_txt);
mStartButton = findViewById(R.id.start_button);
mLineChart = findViewById(R.id.line_chart);
mRandom = new Random();
mStringBuilder = new StringBuilder("现在Y轴数字是0哦");
mEndIndex = 1;
//先创建5个Data数据
mDatas = new Data[]{new Data(1,5),new Data(2,8),
new Data(3,10),new Data(4,13),new Data(5,16)};
for (Data data :mDatas){
mEntries.add(new Entry(data.getValueX(),data.getValueY()));
}
LineDataSet dataSet = new LineDataSet(mEntries,"number");
LineData lineData = new LineData(dataSet);
mLineChart.setData(lineData);
mLineChart.invalidate();
mHandler = new Handler(){
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
if (msg.what==TAG){
updateTxt(msg);
updateChart(msg);
}
}
};
mThread = new Thread(new Runnable() {
@Override
public void run() {
int corrX = 6;//已经有了五个数据，下一个数据的x坐标从6开始
while (true){
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
int corrY = mRandom.nextInt(20) + 5;
Message message = Message.obtain();
message.arg1 = corrY;
message.arg2 = corrX;
message.what = TAG;
mHandler.sendMessage(message);
corrX += 1;
}
}
});
mStartButton.setOnClickListener((View v) -> mThread.start());
}
//更新SpannableString类型的文本需要用该函数判断更新数字的位数
private int endIndex(int i){
int index = 0;
while (i!=0){
i = i/10;
index += 1;
}
return index;
}
//更新显示当前值的TextView
private void updateTxt(Message msg){
mStringBuilder.replace(7,7 + mEndIndex, msg.arg1 + "");//将原来的数字替换
SpannableStringBuilder spannableStringBuilder = new SpannableStringBuilder(mStringBuilder);
ForegroundColorSpan foregroundColorSpan = new ForegroundColorSpan(Color.BLUE);
RelativeSizeSpan relativeSizeSpan = new RelativeSizeSpan(1.5f);
mEndIndex = endIndex(msg.arg1);//新的y值的位数
spannableStringBuilder.setSpan(foregroundColorSpan,7,7 + mEndIndex, Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
spannableStringBuilder.setSpan(relativeSizeSpan,7,7 + mEndIndex, Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
mTextView.setText(spannableStringBuilder);
}
//刷新折线图
private void updateChart(Message msg){
mEntries.add(new Entry(msg.arg2,msg.arg1));
LineDataSet dataSet = new LineDataSet(mEntries,"number");
LineData lineData = new LineData(dataSet);
mLineChart.setData(lineData);
mLineChart.invalidate();
}
}
Data类如下
public class Data {
private int valueX;
private int valueY;
public Data(int x,int y){
this.valueX = x;
this.valueY = y;
}
public int getValueX() {
return valueX;
}
public void setValueX(int valueX) {
this.valueX = valueX;
}
public int getValueY() {
return valueY;
}
public void setValueY(int valueY) {
this.valueY = valueY;
}
}
2、RxJava实现
Rxjava在处理复杂的多线程事件逻辑时比Handler/Async等要简单易用可靠。用来写这个demo算是大炮打蚊子，纯当练手了。
MainActivity
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private LineChart mLineChart;
private TextView mTextView;
private Button mStartButton;
private List mEntryList = new ArrayList<>();
private Random mRandom;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mLineChart = findViewById(R.id.line_chart);
mStartButton = findViewById(R.id.start_button);
mTextView = findViewById(R.id.value_txt);
mStartButton.setOnClickListener((View v) -> intervalObservable());
}
private void intervalObservable() {
mRandom = new Random();
Observable.interval(1000, 1000, TimeUnit.MILLISECONDS)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Consumer() {
@Override
public void accept(Long aLong) throws Exception {
Log.e("intervalObservable", Thread.currentThread().getName());
Long x = aLong;
int y = mRandom.nextInt(10);
Data data = new Data(x, y);
x++;
mEntryList.add(new Entry(data.getX(), data.getY()));
LineDataSet dataSet = new LineDataSet(mEntryList, "label");
LineData lineData = new LineData(dataSet);
mLineChart.setData(lineData);
mLineChart.invalidate();
mTextView.setText("当前y值为" + y);
}
});
}
}
写的时候发现如果直接用Observable.create()生成数据的话，速度太快，MPAndroidChart刷新不过来，一片空白。所以改用Observable.interval()，每个1秒生成一个，但是这个函数只能返回一个Observable
还要注意的是，Observable.interval()默认订阅Schedulers.computation这个线程，如果有UI更新的话，需要在主线程中进行观察，即调用observeOn(AndroidSchedulers.mainThread())。
但是我发现一个很神奇的事，MPAndroidChart可以在非UI线程中进行刷新。
难道只能用Observal.interval()吗?其实不是的，我发现只要使被观察者线程休眠一小段时间，就能让折线图刷新出来，代码如下
Observable.create(new ObservableOnSubscribe() {
@Override
public void subscribe(@NonNull ObservableEmitter e) throws Exception {
Long x = 0l;
Random random = new Random();
while(x < 1000) {
int y = random.nextInt(10);
Data data = new Data(x, y);
e.onNext(data);
x++;
Thread.sleep(1000);//休眠1秒
}
Log.e(TAG, "Observable thread is : " + Thread.currentThread().getName());
}
}).subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(data -> {
Log.i("onNext(Data data)", data.toString());
Log.e(TAG, "Observer thread is :" + Thread.currentThread().getName());
mEntryList.add(new Entry(data.getX(), data.getY()));
LineDataSet dataSet = new LineDataSet(mEntryList, "label");
LineData lineData = new LineData(dataSet);
mLineChart.setData(lineData);
mLineChart.invalidate();
mTextView.setText("当前值为" + data.getY());
});
其实在订阅者线程中休眠也可以正常接收到数据，但订阅者线程一般是UI线程，休眠的话，UI就不会更新了。
另外，被观察者的线程没有休眠的话，即使被观察者数据发送的很快，订阅者在onNext()即使进行了线程休眠，数据也能全部接收到，不会出现事件丢失的情况，这一点让我比较疑惑。
如果被观察者的线程调用了Thread.sleep(1)，而观察者在onNext()中调用了Thread.sleep(1000)，那么会出现上下游事件处理速率不匹配，事件丢失，OOM等情况。
这个时候就要用支持背压的Flowable了。
其实用Flowable同样可以实现折线图更新，代码如下：
Flowable.create(new FlowableOnSubscribe() {
@Override
public void subscribe(FlowableEmitter e) throws Exception{
Long x = 0l;
Random random = new Random();
while(x < 1000) {
int y = random.nextInt(10);
Data data = new Data(x, y);
e.onNext(data);
x++;
Thread.sleep(1000);
}
Log.e(TAG, "Observable thread is : " + Thread.currentThread().getName());
}
}, BackpressureStrategy.BUFFER).subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber() {
Subscription mSubscription;
@Override
public void onSubscribe(Subscription s) {
mSubscription = s;
s.request(1);
}
@Override
public void onNext(Data data) {
Log.i("onNext(Data data)", data.toString());
Log.e(TAG, "Observer thread is :" + Thread.currentThread().getName());
mEntryList.add(new Entry(data.getX(), data.getY()));
LineDataSet dataSet = new LineDataSet(mEntryList, "label");
LineData lineData = new LineData(dataSet);
mLineChart.setData(lineData);
mLineChart.invalidate();
mTextView.setText("当前值为" + data.getY());
mSubscription.request(1);
}
@Override
public void onError(Throwable t) {
}
@Override
public void onComplete() {
}
});