Add progress implementation for android

src/android/src/main/java/com/RNFetchBlob/RNFetchBlob.java

     }
 
     @ReactMethod
-    public void fetchBlob(String method, String url, ReadableMap headers, String body, final Callback callback) {
+    public void fetchBlob(String taskId, String method, String url, ReadableMap headers, String body, final Callback callback) {
 
         try {
             Uri uri = Uri.parse(url);
             }
 
             // create handler
-            AsyncHttpResponseHandler handler = new RNFetchBlobHandler(callback);
+            AsyncHttpResponseHandler handler = new RNFetchBlobHandler(this.getReactApplicationContext(), taskId, callback);
 
             // send request
             switch(method.toLowerCase()) {
     }
 
     @ReactMethod
-    public void fetchBlobForm(String method, String url, ReadableMap headers, ReadableArray body, final Callback callback) {
+    public void fetchBlobForm(String taskId, String method, String url, ReadableMap headers, ReadableArray body, final Callback callback) {
 
         try {
             Uri uri = Uri.parse(url);
             }
 
             // create handler
-            AsyncHttpResponseHandler handler = new RNFetchBlobHandler(callback);
+            AsyncHttpResponseHandler handler = new RNFetchBlobHandler(this.getReactApplicationContext(), taskId, callback);
 
             // send request
             switch(method.toLowerCase()) {

src/android/src/main/java/com/RNFetchBlob/RNFetchBlobHandler.java

 package com.RNFetchBlob;
 
 import com.facebook.react.bridge.Callback;
+import com.facebook.react.bridge.WritableMap;
+import com.facebook.react.bridge.Arguments;
+import com.facebook.react.bridge.ReactContext;
+import com.facebook.react.modules.core.DeviceEventManagerModule;
 import com.loopj.android.http.AsyncHttpResponseHandler;
 import com.loopj.android.http.Base64;
 
 public class RNFetchBlobHandler extends AsyncHttpResponseHandler {
 
     Callback onResponse;
+    ReactContext mCtx;
+    String mTaskId;
+
+    RNFetchBlobHandler(ReactContext ctx, String taskId, Callback onResponse) {
 
-    RNFetchBlobHandler(Callback onResponse) {
         this.onResponse = onResponse;
+        this.mTaskId = taskId;
+        this.mCtx = ctx;
     }
 
     @Override
     @Override
     public void onProgress(long bytesWritten, long totalSize) {
         super.onProgress(bytesWritten, totalSize);
+
+        // on progress, emit RNFetchBlobProgress event with ticketId, bytesWritten, and totalSize
+        WritableMap args = Arguments.createMap();
+        args.putString("taskId", this.mTaskId);
+        args.putString("written", String.valueOf(bytesWritten));
+        args.putString("total", String.valueOf(totalSize));
+
+        // emit event to js context
+        this.mCtx.getJSModule(DeviceEventManagerModule.RCTDeviceEventEmitter.class)
+                 .emit("RNFetchBlobProgress" + this.mTaskId, args);
     }
 
     @Override