基于LiveData的Service刷新UI

前言

使用单例拓展LiveData对象，可以在您的app全局使用。LiveData一旦与service构建联系，通过observer观察者，即可更新数据源。
下面举例说明

构建SyncLiveData继承LiveData构建SyncServiceSyncFragmentFragment通过SyncLiveData观察LiveData数据发生变化后，可以做相关UI更新。LiveData通过Service发生数据更新。

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一、构建SyncLiveData类

public class SyncLiveData extends LiveData<SpannableStringBuilder> {
    private static SynLiveData sInstance;
    private final static SpannableStringBuilder log = new SpannableStringBuilder("");

    @MainThread
    public static SynLiveData get() {
        if (sInstance == null) {
            sInstance = new SynLiveData();
        }
        return sInstance;
    }

    private SynLiveData() {
    }

    public void appendLog(String text) {
        log.append(text);
        postValue(log);
    }

    public void appendLog(Spanned text) {
        log.append(text);
        postValue(log);
    }
}

二、在SyncService处理数据更新

下面会更新 LiveData

SyncLiveData.get().appendLog(message);

使用LiveData的方法setValue(…) or postValue(…)通知观察者刷新UI

SyncLiveData.get().setValue(message);

三、构建UI类SyncFragment

public void onViewCreated(@NonNull View view, Bundle savedInstanceState) {
    //...
    // Create the observer which updates the UI.
    final Observer<SpannableStringBuilder> ETAObserver = new Observer<SpannableStringBuilder>() {
        @Override
        public void onChanged(@Nullable final SpannableStringBuilder spannableLog) {
            // Update the UI, in this case, a TextView.
            getActivity().runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    textViewLog.setText(spannableLog);
                }
            });
        }
    };
    // Observe the LiveData, passing in this activity/fragment as the LifecycleOwner and the observer.
    SyncLiveData.get().observe(getViewLifecycleOwner(), ETAObserver);
    //...
}

下面是activity观察模式

SyncLogLiveData.get().observe(this, ETAObserver);

当然，您可以捕获LiveData的数据

SyncLogLiveData.get().getValue();

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