Android 请求网络时实现自动 Loading 的一种方式

诉求

希望请求网络时自动弹出 Loading，网络请求结束时自动取消 Loading；如果有多个请求并行执行，希望最后一个请求结束时才取消 Loading。

实现

• SimpleRetrofit.kt

object SimpleRetrofit {

    private val mCallMap = ConcurrentHashMap<Call, Loading>()
    private val mActivityList = CopyOnWriteArrayList<Loading>()

    fun init(context: Context, builder: OkHttpClient.Builder): OkHttpClient.Builder {
        (context.applicationContext as Application).registerActivityLifecycleCallbacks(
            object : EmptyActivityLifecycleCallbacks() {
                override fun onActivityCreated(activity: Activity, savedInstanceState: Bundle?) {
                    if (activity is Loading) {
                        mActivityList.add(activity)
                    }
                }

                override fun onActivityDestroyed(activity: Activity) {
                    if (activity is Loading) {
                        mActivityList.remove(activity)
                    }
                }
            })

        builder.eventListener(object : EventListener() {
            override fun callStart(call: Call) {
                super.callStart(call)
                mActivityList.lastOrNull()?.let {
                    mCallMap[call] = it
                }
                handleLoading(true, call)
            }

            override fun callEnd(call: Call) {
                super.callEnd(call)
                handleLoading(false, call)
                mCallMap.remove(call)
            }

            override fun callFailed(call: Call, ioe: IOException) {
                super.callFailed(call, ioe)
                handleLoading(false, call)
                mCallMap.remove(call)
            }
        })

        return builder
    }

    private fun handleLoading(show: Boolean, call: Call) {
        mCallMap[call]?.handleLoading(show)
    }

}

• Loading.kt

interface Loading {

    companion object {
        // we must use a tag to find the specified fragment.
        // you can not hold an instance of DialogFragment to call dialog.show()/dialog.hide().
        // for if you rotate the screen, then activity will be re-created, then you will
        // hold another new instance of DialogFragment, at this time you call hide() without show()
        // called before, exception will be thrown.
        // eg: Activity#onCreate -> dialog=DialogFragment() -> dialog.show() ->
        //     Activity#onCreate -> dialog=DialogFragment() -> dialog.hide() -> crash
        private const val TAG_LOADING_DIALOG_FRAGMENT = "TAG_LOADING_DIALOG_FRAGMENT"
    }

    var mLoading: Int
    var mHidePending: Boolean
    val mHandler: Handler

    fun handleLoading(show: Boolean) {
        if (show) {
            mHandler.post { showLoading() }
        } else {
            mHandler.post { hideLoading() }
        }
    }

    fun onDialogShown(dialog: DialogFragment) {
        if (mHidePending) {
            mHidePending = false
            dialog.dismiss()
        }
    }

    private fun showLoading() {
        if (mLoading++ > 0) {
            return
        }

        if (this is AppCompatActivity) {
            val fragment = supportFragmentManager.findFragmentByTag(TAG_LOADING_DIALOG_FRAGMENT)
            if (fragment == null) {
                SimpleLoadingDialog.newInstance()
                    .show(supportFragmentManager, TAG_LOADING_DIALOG_FRAGMENT)
            }
        }
    }

    private fun hideLoading() {
        if (mLoading-- > 1) {
            return
        }

        if (this is AppCompatActivity) {
            val dialog = supportFragmentManager.findFragmentByTag(TAG_LOADING_DIALOG_FRAGMENT)
            if (null != dialog && dialog.isResumed) {
                (dialog as DialogFragment).dismiss()
            } else {
                mHidePending = true
            }
        }
    }

}

• LoadingActivity.kt

abstract class LoadingActivity : AppCompatActivity(), Loading {
    override var mLoading = 0
    override val mHandler = Handler(Looper.getMainLooper())
    override var mHidePending = false
}

• SimpleLoadingDialog.kt

class SimpleLoadingDialog : DialogFragment() {

    companion object {
        fun newInstance(): SimpleLoadingDialog {
            val dialog = SimpleLoadingDialog()
            dialog.arguments = Bundle().apply {
                // add arguments
            }
            return dialog
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        isCancelable = false
    }

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        return ProgressBar(requireContext())
    }

    override fun onResume() {
        super.onResume()
        val activity = requireActivity()
        if (activity is Loading) {
            activity.onDialogShown(this)
        }
    }

}

兼容

如果还有一部分请求是不需要弹 Loading 的怎么办？使用另一个 OkHttpClient 实例即可。