自己写一个flutter插件

某些场景下或者现有pub插件无法满足我们的需求的时候需要自己写一个插件

现在有这样一个场景,需要给定一个图片的url,然后下载图片到指定目录中(/storage/emulated/0/Android/data/com.zx.plugintest/files/Caches)。现在有一个插件,image_gallery_saver ,但它将网络文件保存在了我们的相册目录中。

 

1、在flutter根目录下新建一个flutter 插件

打开androidstudio terminal 

flutter create --template=plugin  --org com.zx --platforms=android,ios -a java -i swift save_img_plugin

其中 com.zx 是插件包名的一部分,save_img_plugin 是插件的名称。插件的完整包名为 com.zx.save_img_plugin

为什么没有使用IDE 的选项创建呢,我创建出来没有android 和 ios的原生工程目录 

参考 https://blog.csdn.net/zytry/article/details/108997168

2、pubspec.yaml 添加插件

save_img_plugin:
  path: save_img_plugin

pub get 一下

3、在插件的lib\save_pic_plugin.dart添加如下代码

static Future saveImage(Uint8List imageBytes,
      {int quality = 80, String name}) async {
    assert(imageBytes != null);
    final result =
    await _channel.invokeMethod('saveImageToLocal', <String, dynamic>{
      'imageBytes': imageBytes,
      'quality': quality,
      'name': name,
    });
    return result;
  }

这里的代码是给其他flutter调用者 提供的外部接口。

4、实现native调用方法

package com.zx.save_img_plugin;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

import androidx.annotation.NonNull;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

import io.flutter.Log;
import io.flutter.embedding.engine.plugins.FlutterPlugin;
import io.flutter.plugin.common.MethodCall;
import io.flutter.plugin.common.MethodChannel;
import io.flutter.plugin.common.MethodChannel.MethodCallHandler;
import io.flutter.plugin.common.MethodChannel.Result;

/** SaveImgPlugin */
public class SaveImgPlugin implements FlutterPlugin, MethodCallHandler {

  private static final String TAG = "SaveImgPlugin";
  private MethodChannel channel;
  private Context mContext;

  @Override
  public void onAttachedToEngine(@NonNull FlutterPluginBinding flutterPluginBinding) {
    channel = new MethodChannel(flutterPluginBinding.getBinaryMessenger(), "save_img_plugin");
    channel.setMethodCallHandler(this);
    mContext = flutterPluginBinding.getApplicationContext();
  }

  @Override
  public void onMethodCall(@NonNull MethodCall call, @NonNull Result result) {
    Log.d(TAG,"---onMethodCall---");
    if (call.method.equals("saveImageToLocal")) {

      byte[] image = null;
      int quality = 100;
      String name = "splash.jpg";
      if (null != call.argument("imageBytes")) {
        image = call.argument("imageBytes");
      } else {
        result.error("the argument imageBytes is null","","");
      }

      if (null != call.argument("name")) {
        name = call.argument("name");
      }

      if (null != call.argument("quality")) {
        quality = call.argument("quality");
        if(quality <= 0 || quality>100) {
          result.error("the quality is in range(0,100]","","");
        }
      }
      result.success(saveImageToLocal(BitmapFactory.decodeByteArray(image,0,image.length), quality, name));
    }
  }

  private boolean saveImageToLocal(Bitmap bmp, int quality, String name) {
    Log.d(TAG,"---saveImageToLocal---");
    Context context = mContext.getApplicationContext();
    String cacheDir = context.getExternalFilesDir("Caches").getPath();
    Log.d(TAG,"---cacheDir---" + cacheDir);
    File file = new File(cacheDir + File.separator + name);  //将图片保存到刚创建好的目录下
    try {
      FileOutputStream out = new FileOutputStream(file);
      if (bmp != null) {
        bmp.compress(Bitmap.CompressFormat.JPEG, quality, out);
      }
      out.close();
      return true;
    } catch (IOException e) {
      e.printStackTrace();
    }
    return false;
  }

  @Override
  public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
    channel.setMethodCallHandler(null);
  }
}

注意 :

1、flutter (save_pic_plugin.dart)传递的参数 saveImageToLocal 必须和 原生 if (call.method.equals("saveImageToLocal"))  中判断的名称相同才能进入对应逻辑。

2、平台通道数据类型支持

平台通道使用标准消息编/解码器对消息进行编解码,它可以高效的对消息进行二进制序列化与反序列化。由于Dart与原生平台之间数据类型有所差异,下面我们列出数据类型之间的映射关系。

Dart Android iOS
null null nil (NSNull when nested)
bool java.lang.Boolean NSNumber numberWithBool:
int java.lang.Integer NSNumber numberWithInt:
int, 如果不足32位 java.lang.Long NSNumber numberWithLong:
int, 如果不足64位 java.math.BigInteger FlutterStandardBigInteger
double java.lang.Double NSNumber numberWithDouble:
String java.lang.String NSString
Uint8List byte[] FlutterStandardTypedData typedDataWithBytes:
Int32List int[] FlutterStandardTypedData typedDataWithInt32:
Int64List long[] FlutterStandardTypedData typedDataWithInt64:
Float64List double[] FlutterStandardTypedData typedDataWithFloat64:
List java.util.ArrayList NSArray
Map java.util.HashMap NSDictionary

当在发送和接收值时,这些值在消息中的序列化和反序列化会自动进行。

在android 清单文件中添加两个权限

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.INTERNET"/>

至于权限怎么添加和使用,方式如下:

5、新建一个permission.dart

import 'package:permission_handler/permission_handler.dart';


Future<bool> requestStoragePermission() async {
  final storageStatus = await PermissionHandler().requestPermissions([PermissionGroup.storage]);
  if (storageStatus[PermissionGroup.storage] == PermissionStatus.granted) {
    return true;
  } else {
    return false;
  }
}

6、使用

import 'Permission.dart' as Permission;

void savePic() async {
    Permission.requestStoragePermission().then((value)  async {
      if(value) {
        var response = await Dio().get(
            "https://ss0.baidu.com/94o3dSag_xI4khGko9WTAnF6hhy/image/h%3D300/sign=a62e824376d98d1069d40a31113eb807/838ba61ea8d3fd1fc9c7b6853a4e251f94ca5f46.jpg",
            options: Options(responseType: ResponseType.bytes));
        SaveImgPlugin.saveImage(Uint8List.fromList(response.data),quality:100,name:'mypic1.png').then((value) {
          setState(() {
            tip = 'down load over';
          });
        });
      }
    });
  }

完后在日志中找到 ---cacheDir---/storage/emulated/0/Android/data/com.zx.plugintestapp/files/Caches  ,这个里面就有我们下载好的图片文件。

ok,整个插件的基础开发就是这些了。

 

 

 

 

 

 

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