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用 kotlin 来实现 dsl 风格的编程

Anko

Anko 是一个 DSL (Domain-Specific Language), 它是JetBrains出品的,用 Kotlin 开发的安卓框架。它主要的目的是用来替代以前XML的方式来使用代码生成UI布局。

先来看一个直观的例子

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent">

    <EditText
        android:id="@+id/todo_title"
        android:layout_width="match_parent"
        android:layout_heigh="wrap_content"
        android:hint="@string/title_hint" />

    <!-- Cannot directly add an inline click listener as onClick delegates implementation to the activity -->
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/add_todo" />

</LinearLayout>复制代码

使用Anko之后,可以用代码实现布局,并且button还绑定了点击事件。

verticalLayout {
    var title = editText {
        id = R.id.todo_title
        hintResource = R.string.title_hint
    }
    button {
        textResource = R.string.add_todo
        onClick { view -> {
                // do something here
                title.text = "Foo"
            }
        }
    }
}复制代码

可以看到 DSL 的一个主要优点在于,它需要很少的时间即可理解和传达某个领域的详细信息。

简单封装OkHttp

OkHttp是一个成熟且强大的网络库,在Android源码中已经使用OkHttp替代原先的HttpURLConnection。很多著名的框架例如Picasso、Retrofit也使用OkHttp作为底层框架。在这里我对OkHttp做一下简单的封装,其实封装得有点粗暴只是为了演示如何实现dsl。

import io.reactivex.BackpressureStrategy
import io.reactivex.Flowable
import io.reactivex.schedulers.Schedulers
import okhttp3.OkHttpClient
import okhttp3.Request
import okhttp3.RequestBody
import okhttp3.Response
import java.util.concurrent.TimeUnit

/**
 * Created by Tony Shen on 2017/6/1.
 */
class RequestWrapper {

    var url:String? = null

    var method:String? = null

    var body: RequestBody? = null

    var timeout:Long = 10

    internal var _success: (String) -> Unit = { }
    internal var _fail: (Throwable) -> Unit = {}

    fun onSuccess(onSuccess: (String) -> Unit) {
        _success = onSuccess
    }

    fun onFail(onError: (Throwable) -> Unit) {
        _fail = onError
    }
}

fun http(init: RequestWrapper.() -> Unit) {
    val wrap = RequestWrapper()

    wrap.init()

    executeForResult(wrap)
}

private fun executeForResult(wrap:RequestWrapper) {

    Flowable.create<Response>({
        e -> e.onNext(onExecute(wrap))
    }, BackpressureStrategy.BUFFER)
            .subscribeOn(Schedulers.io())
            .subscribe(
                    { resp ->
                        wrap._success(resp.body()!!.string())
                    },

                    { e -> wrap._fail(e) })
}

private fun onExecute(wrap:RequestWrapper): Response? {

    var req:Request? = null
    when(wrap.method) {

        "get","Get","GET" -> req =Request.Builder().url(wrap.url).build()
        "post","Post","POST" -> req = Request.Builder().url(wrap.url).post(wrap.body).build()
        "put","Put","PUT" -> req = Request.Builder().url(wrap.url).put(wrap.body).build()
        "delete","Delete","DELETE" -> req = Request.Builder().url(wrap.url).delete(wrap.body).build()
    }

    val http = OkHttpClient.Builder().connectTimeout(wrap.timeout, TimeUnit.SECONDS).build()
    val resp = http.newCall(req).execute()
    return resp
}复制代码

封装完OkHttp之后,看看如何来编写get请求

        http {

            url = "http://www.163.com/"

            method = "get"

            onSuccess {
                string -> L.i(string)
            }

            onFail {
                e -> L.i(e.message)
            }
        }复制代码

是不是很像以前用jquery来写ajax?

post请求也是类似的,只不过多了body

        var json = JSONObject()
        json.put("xxx","yyyy")
        ....

        val postBody = RequestBody.create(MediaType.parse("application/json; charset=utf-8"),json.toString())

        http {

            url = "https://......"

            method = "post"

            body = postBody

            onSuccess {
                string -> L.json(string)
            }

            onFail {
                e -> L.i(e.message)
            }
        }复制代码

封装自己的图像处理框架

cv4j 是我们开发的实时图像处理框架。最早使用滤镜的方式如下:

        CV4JImage cv4jImage = new CV4JImage(bitmap);
        CommonFilter filter = new NatureFilter();
        Bitmap newBitMap = filter.filter(cv4jImage.getProcessor()).getImage().toBitmap();
        image.setImageBitmap(newBitMap);复制代码

后来增加了RxJava封装的版本

RxImageData.bitmap(bitmap).addFilter(new NatureFilter()).into(image);复制代码

现在Kotlin项目除了可以使用上述两种方式之外,还多了一种方式。

        cv4j {
            bitmap = BitmapFactory.decodeResource(resources, R.drawable.test_io)

            filter = NatureFilter()

            imageView = image
        }复制代码

这个dsl是如何封装的呢?其实是对RxJava版本进一步封装。

/**
 * Copyright (c) 2017-present, CV4J Contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.cv4j.rxjava

import android.app.Dialog
import android.graphics.Bitmap
import android.widget.ImageView
import com.cv4j.core.datamodel.CV4JImage
import com.cv4j.core.filters.CommonFilter

/**
 * only for Kotlin code,this class provides the DSL style for cv4j
 */
class Wrapper {

    var bitmap:Bitmap? = null

    var cv4jImage: CV4JImage? = null

    var bytes:ByteArray? = null

    var useCache:Boolean = true

    var imageView: ImageView? = null

    var filter: CommonFilter? = null

    var dialog: Dialog? = null
}

fun cv4j(init: Wrapper.() -> Unit) {
    val wrap = Wrapper()

    wrap.init()

    render(wrap)
}

private fun render(wrap: Wrapper) {

    if (wrap.bitmap!=null) {

        if (wrap.filter!=null) {
            RxImageData.bitmap(wrap.bitmap).dialog(wrap.dialog).addFilter(wrap.filter).isUseCache(wrap.useCache).into(wrap.imageView)
        } else {
            RxImageData.bitmap(wrap.bitmap).dialog(wrap.dialog).isUseCache(wrap.useCache).into(wrap.imageView)
        }

    } else if (wrap.cv4jImage!=null) {

        if (wrap.filter!=null) {
            RxImageData.image(wrap.cv4jImage).dialog(wrap.dialog).addFilter(wrap.filter).isUseCache(wrap.useCache).into(wrap.imageView)
        } else {
            RxImageData.image(wrap.cv4jImage).dialog(wrap.dialog).isUseCache(wrap.useCache).into(wrap.imageView)
        }
    } else if (wrap.bytes!=null) {

        if (wrap.filter!=null) {
            RxImageData.bytes(wrap.bytes).dialog(wrap.dialog).addFilter(wrap.filter).isUseCache(wrap.useCache).into(wrap.imageView)
        } else {
            RxImageData.bytes(wrap.bytes).dialog(wrap.dialog).isUseCache(wrap.useCache).into(wrap.imageView)
        }
    }

}复制代码

来看一下程序的最终效果图

dsl风格使用滤镜.png

cv4j 目前已经支持了几十种滤镜,当然除了滤镜还有其他功能,感兴趣的童鞋可以看我们的源码:)。

总结

使用dsl的代码风格,可以让程序更加直观和简洁。如果使用Kotlin来开发项目的话,完全可以尝试一下。

公司的sdk项目我也考虑引入Kotlin,我已经写了一个module用于封装原先的sdk,这个module只适用于Kotlin项目。用于简化初始化sdk和实现deep link的注册服务。

初始化sdk.jpg

注册各个mLink服务.jpg

可以感受一下,使用dsl是不是比原先的代码更加简洁和直观呢?
另外,众所周知的Gradle也是基于DSL的Java构建工具。

参考资料:

  1. <<使用kotlin写自己的dsl>>
  2. Type-Safe Builders
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