使用Python编写iOS原生应用的框架设计思考(首篇)

一、引子

使用Python编写iOS原生应用，为何有这样的想法，其实本来是源于对JS类的跨平台框架的学习。熟悉原生开发的同学们都知道，对于可跨平台的原生框架，使用JS实现的占了大半，其原因是由于Apple内置了JavaScriptCore这样一个JS引擎，使得JavaScript与Objective-C的交互变得非常容易，能够交互，我们就可以容易的编写出各种各样的桥来为JS端提供原生功能，随着原生端桥的全面支持和JS端组件的丰富，一个完整的矿平台框架就诞生了。虽说这是一个庞大的工程，但是实现思路并不深奥，之前也有博客也有介绍：

https://my.oschina.net/u/2340880/blog/856321

有了JavaScript框架实现思路的基础，那么不免就很容易想到，其实在语言层面，语言可以做的事情都是相似的，只要有对应的引擎可用，那么原则上说，任何语言都可以编写iOS应用程序，只有难以与方便与否的差别。对于Python来说，其的确有iOS版本的解释器可用。

二、在iOS平台使用Python解释器

Github上有很多有趣的项目，其中有一个项目可以将Python源码编译成可以在iOS平台运行的Framework，其地址如下：

https://github.com/beeware/Python-Apple-support

有了这个工具，我们可以选择任意版本的Python来将其打包成Framework在iOS平台运行，当然如果你对版本没有特殊的要求，你也可以直接从下面的地址下载已经打包好的Framewok使用：

https://github.com/pybee/Python-iOS-support/releases

下载完成后，会得到两个Framework，将他们添加进工程，并进行链接，如下图：

需要注意，对于Python.framework要更特殊一点，我们需要将其拷贝进工程的Bundle中，以便后续使用。

三、编写桥接文件

这部分主要有Objective-C实现，用来启动Python引擎，加载Python业务代码的入口文件，做各种原生组件与Python组件的桥接等。首先编写一个头文件用来进行静态变量和宏的定义，如下：

//
//  BrdgeDefine.h
//  PyNativeDemo
//
//  Created by 珲少 on 2020/4/30.
//  Copyright © 2020 jaki. All rights reserved.
//

#ifndef BrdgeDefine_h
#define BrdgeDefine_h
#import <Python/Python.h>

#define INTERFACE_INSTANCE + (instancetype)sharedInstance;

#define IMPLEMENTATION_INSTANCE             \
+ (instancetype)sharedInstance {            \
    static id instance = nil;               \
    static dispatch_once_t onceToken;       \
    dispatch_once(&onceToken, ^{            \
        if (!instance) {                    \
            instance = [[self alloc] init]; \
        }                                   \
    });                                     \
    return instance;                        \
}

#define SELF_INSTANCE [self.class sharedInstance]


#endif /* BrdgeDefine_h */

编写Python桥的引擎类，如下：

BridgeEnigine.h:

#import <Foundation/Foundation.h>
#import "BrdgeDefine.h"
#import <UIKit/UIKit.h>
NS_ASSUME_NONNULL_BEGIN

@interface BridgeEngine : NSObject

INTERFACE_INSTANCE

+ (UIViewController *)setupEngine;

@end

NS_ASSUME_NONNULL_END

BridgeEnigine.m:

#import "BridgeEngine.h"
#import "DisplayRender.h"
#import "PythonRun.h"

@interface BridgeEngine ()

@end

@implementation BridgeEngine

IMPLEMENTATION_INSTANCE

+ (UIViewController *)setupEngine {
    [SELF_INSTANCE startEngine];
    [SELF_INSTANCE loadLib];
    [SELF_INSTANCE runMain];
    return [SELF_INSTANCE renderRoot];
}

- (void)startEngine {
    NSString* frameworkPath = [NSString stringWithFormat:@"%@/Resources",[SELF_INSTANCE p_pythonFrameworkPath]];
    wchar_t *pythonHome = [SELF_INSTANCE stingTowWchar_t:frameworkPath];
    Py_SetPythonHome(pythonHome);
    Py_Initialize();
    PyEval_InitThreads();
    if (Py_IsInitialized()) {
        NSLog(@"😄初始化环境成功😄");
    } else {
        NSLog(@"😢Python初始化环境失败😢");
        exit(0);
    }
}

- (void)loadLib {
    NSString *path = [NSString stringWithFormat:@"import sys\nsys.path.append(\"%@\")",[[NSBundle mainBundle] resourcePath]];
    PyRun_SimpleString([path UTF8String]);
    NSLog(@"😄lib加载成功😄");
}

- (void)runMain {
    PyObject * pModule = PyImport_ImportModule([@"main" UTF8String]);//导入模块
    [PythonRun sharedInstance].mainItemDic = PyModule_GetDict(pModule);
}

- (UIViewController *)renderRoot {
    return [[DisplayRender sharedInstance] renderRoot:@"Main"];
}

- (wchar_t *)stingTowWchar_t:(NSString*)string {
    return (wchar_t*)[string cStringUsingEncoding:NSUTF32StringEncoding];
}

- (NSString*)p_pythonFrameworkPath{
    NSString* path = [[NSBundle mainBundle] pathForResource:@"Python" ofType:@"framework"];
    return path;
}

- (void)dealloc {
    Py_Finalize();
}

@end

其中有使用到DisplayRender，由于Python没有办法主动调用原生，初步设想，让这个类通过帧刷新来负责对界面的渲染维护，编码如下：

DisplayRender.h:

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
#import "BrdgeDefine.h"

NS_ASSUME_NONNULL_BEGIN

@interface DisplayRender : NSObject

INTERFACE_INSTANCE

- (UIViewController *)renderRoot:(NSString *)main;

@end

NS_ASSUME_NONNULL_END

DisplayRender.m:

#import "DisplayRender.h"
#import "PythonRun.h"
#import "BridgeColor.h"
#import "ViewMaker.h"

@interface DisplayRender ()

@property (nonatomic, strong) UIViewController *rootController;

@property (nonatomic, strong) NSMutableArray<UIView *> *subViews;

@end

@implementation DisplayRender

IMPLEMENTATION_INSTANCE

- (UIViewController *)renderRoot:(NSString *)main {
    NSDictionary *root = [[PythonRun sharedInstance] run:[main UTF8String] method:[@"render_main_view" UTF8String]];
    NSLog(@"AppLaunchFinish🙅‍♀️");
    [self renderController:root];
    return self.rootController;
}

- (void)renderController:(NSDictionary *)info {
    [self.subViews enumerateObjectsUsingBlock:^(UIView *  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        [obj removeFromSuperview];
    }];
    [self.subViews removeAllObjects];
    
    NSString *bg = [info objectForKey:@"color"];
    self.rootController.view.backgroundColor = [BridgeColor colorWith:bg];
    NSArray *views = [info objectForKey:@"subViews"];
    for (NSUInteger i = 0; i < views.count; i++) {
        id view = [ViewMaker makerView:[views[i] objectForKey:@"name"]];
        for (NSString *key in [views[i] allKeys]) {
            if (![key isEqualToString:@"name"]) {
                [view setValue:[views[i] objectForKey:key] forKey:key];
            }
        }
        [self.subViews addObject:view];
        [self.rootController.view addSubview:view];
    }
}

- (UIViewController *)rootController {
    if (!_rootController) {
        _rootController = [[UIViewController alloc] init];
    }
    return _rootController;
}

@end

PythonRun是一个工具类，起来调用Python解释器对Python代码进行执行，并通过数据与原生端进行交互，编码如下：

PythonRun.h:

#import <Foundation/Foundation.h>
#import "BrdgeDefine.h"

NS_ASSUME_NONNULL_BEGIN

@interface PythonRun : NSObject

INTERFACE_INSTANCE

@property (nonatomic, assign) PyObject *mainItemDic;

- (NSDictionary *)run:(const char *)item method:(const char *)method;

@end

NS_ASSUME_NONNULL_END

PythonRun.m:

#import "PythonRun.h"

@implementation PythonRun

IMPLEMENTATION_INSTANCE

- (NSDictionary *)run:(const char *)item method:(const char *)method {
    PyObject* pClassCalc = PyDict_GetItemString(self.mainItemDic,item);
    PyObject* pInstanceCalc = PyInstanceMethod_New(pClassCalc);
    PyObject* pRet = PyObject_CallMethod(pClassCalc, method, "O", pInstanceCalc);
    return [self dumpInfo:pRet];
}

- (NSDictionary *)dumpInfo:(PyObject *)pRet {
    // 解析数据
    char * resultCString = NULL;
    PyArg_Parse(pRet, "s", &resultCString);
    //将python类型的返回值转换为c
    return [self dumpString:resultCString];
}

- (NSDictionary *)dumpString:(const char *)resultCString {
    NSString *jsonString = [NSString stringWithCString:resultCString encoding:NSUTF8StringEncoding];
    NSDictionary *info = [NSJSONSerialization JSONObjectWithData:[jsonString dataUsingEncoding:NSUTF8StringEncoding] options:NSJSONReadingMutableContainers error:nil];
    NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithDictionary:info];
    for (NSString *k in dic.allKeys) {
        if ([k isEqualToString:@"subViews"]) {
            NSMutableArray *array = [NSMutableArray array];
            for (NSUInteger i = 0; i < [dic[k] count]; i++) {
                  [array addObject:[self dumpString:[dic[k][i] UTF8String]]];
            }
            dic[k] = [array copy];
        }
    }
    NSLog(@"dumpInfo❄️:%@", dic);
    return [dic copy];
}

@end

通过上面3个核心类，一个简易的Python引擎就完整了，下面还需要编写几个转换类，用来将Python对象转换成Objective-C的对象，编写BridgeColor类如下：

BridgeColor.h:

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface BridgeColor : NSObject

+ (UIColor *)colorWith:(NSString *)c;

@end

NS_ASSUME_NONNULL_END

BridgeColor.m:

#import "BridgeColor.h"


@implementation BridgeColor

+ (UIColor *)colorWith:(NSString *)c {
    if ([c isEqualToString:@"red"]) {
        return [UIColor redColor];
    } else if ([c isEqualToString:@"white"]) {
        return [UIColor whiteColor];
    } else if ([c isEqualToString:@"purple"]) {
        return [UIColor purpleColor];
    }
    return [UIColor clearColor];
}

@end

BridgeLabel.h:

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface BridgeLabel : UILabel

@property (nonatomic, strong) NSNumber *left;
@property (nonatomic, strong) NSNumber *top;
@property (nonatomic, strong) NSNumber *width;
@property (nonatomic, strong) NSNumber *height;
@property (nonatomic, strong) NSNumber *font_size;

@property (nonatomic, copy) NSString *background_color;
@property (nonatomic, copy) NSString *t;
@property (nonatomic, copy) NSString *color;

@end

NS_ASSUME_NONNULL_END

BridgeLabel.m:

#import "BridgeLabel.h"
#import "BridgeColor.h"

@implementation BridgeLabel

- (void)setLeft:(NSNumber *)left {
    _left = left;
    self.frame = CGRectMake(left.floatValue, self.frame.origin.y, self.frame.size.width, self.frame.size.height);
}

- (void)setTop:(NSNumber *)top {
    _top = top;
    self.frame = CGRectMake(self.frame.origin.x, top.floatValue, self.frame.size.width, self.frame.size.height);
}

- (void)setWidth:(NSNumber *)width {
    _width = width;
    self.frame = CGRectMake(self.frame.origin.x, self.frame.origin.y, width.floatValue, self.frame.size.height);
}

- (void)setHeight:(NSNumber *)height {
    _height = height;
    self.frame = CGRectMake(self.frame.origin.x, self.frame.origin.y, self.frame.size.width, height.floatValue);
}

- (void)setColor:(NSString *)color {
    _color = color;
    self.textColor = [BridgeColor colorWith:color];
}

- (void)setT:(NSString *)t {
    _t = t;
    self.text = t;
}

- (void)setFont_size:(NSNumber *)font_size {
    _font_size = font_size;
    self.font = [UIFont systemFontOfSize:font_size.intValue];
}

- (void)setBackground_color:(NSString *)background_color {
    _background_color = background_color;
    self.backgroundColor = [BridgeColor colorWith:background_color];
}

@end

ViewMaker.h:

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface ViewMaker : NSObject

+ (id)makerView:(NSString *)name;

@end

NS_ASSUME_NONNULL_END

ViewMaker.m:

#import "ViewMaker.h"
#import "BridgeLabel.h"

@implementation ViewMaker

+ (id)makerView:(NSString *)name {
    if ([name isEqualToString:@"Label"]) {
        return [[BridgeLabel alloc] init];
    }
    return nil;
}

@end

四、编写Python业务代码

在项目中添加两个Python文件，一个命名为main.py作为应用程序的入口文件，一个命名为label.py作为标签组件，main.py文件编写代码如下：

import json
from label import *

class Main():
    def application_Launch(self):
        pass

    def render_main_view(self):
        l = Label("HelloWorld")
        l.color = "red"
        l.font_size = 21
        l.background_color = "white"
        l.left = 100
        l.top = 100
        l.width = 200
        l.height = 30
        
        l2 = Label("hhahha")
        l2.color = "red"
        l2.font_size = 21
        l2.background_color = "white"
        l2.left = 100
        l2.top = 300
        l2.width = 200
        l2.height = 30
        return json.dumps({
            "color": "purple",
            "subViews": [l.render(), l2.render()]
        })

label.py编写代码如下：

import json

class Label:
    def __init__(self, text):
        self.t = text
        self.color = ""
        self.left = 0
        self.top = 0
        self.width = 0
        self.height = 0
        self.font_size = 0
        self.background_color = ""
    
    def render(self):
        return json.dumps({
            "name": "Label",
            "t": self.t,
            "color": self.color,
            "left": self.left,
            "top": self.top,
            "width": self.width,
            "height": self.height,
            "font_size": self.font_size,
            "background_color": self.background_color
        })

到此，一个简易的Python iOS应用Demo工程就搭建完成了，上面代码创建了两个文本标签在页面上，并对组件的部分属性进行了配置，上面实现的每个类都非常简单，作为思路的演示，后续有时间会继续补充完善，并通过博客进行连载介绍，上面工程的运行效果如下图：

五、后续设想

通过DisplayLink来进行页面的变更刷新，为组件增加ID，设计一种算法来实现高效的页面刷新。
将组件的功能完善，添加更多原生组件的支持。
将事件进行包装，定义回调函数，让Python端有用处理事件的能力。
增加更多工具接口，如网络，数据文件操作等。

本篇博客内容比较缩略，你可以在如下地址找到完整的Demo工程：

https://github.com/ZYHshao/PyNativeDemo/tree/master/PyNativeDemo

需要注意，工程较大，原因是我将Python库也放了进去，这样可以保证你下载的代码是可运行的。