Refactor code example to improve code reuse and reduce bloat. If no refname is passed, capture the displayed screen.

example/App.js

       snapshotContentContainer: false
     }
   };
-
-  captureScreenshot = () =>
-    captureScreen(this.state.value)
-      .then(
-        res =>
-          this.state.value.result !== "tmpfile"
-          ? res
-          : new Promise((success, failure) =>
-          // just a test to ensure res can be used in Image.getSize
-          Image.getSize(
-            res,
-            (width, height) => (
-              console.log(res, width, height), success(res)
-            ),
-            failure
-          )
-        )
-      )
-      .then(res =>
-        this.setState({
-          error: null,
-          res,
-          previewSource: {
-            uri:
-              this.state.value.result === "base64"
-                ? "data:image/" + this.state.value.format + ";base64," + res
-                : res
-          }
-        })
-      )
-      .catch(
-        error => (
-          console.warn(error),
-          this.setState({ error, res: null, previewSource: null })
-        )
-      );
-    
-
+  
   snapshot = refname => () =>
-    captureRef(this.refs[refname], this.state.value)
+    (refname ? captureRef(this.refs[refname], this.state.value) : captureScreen(this.state.value))
       .then(
         res =>
           this.state.value.result !== "tmpfile"
             <Btn label="📷 MapView" onPress={this.snapshot("mapview")} />
             <Btn label="📷 WebView" onPress={this.snapshot("webview")} />
             <Btn label="📷 Video" onPress={this.snapshot("video")} />
-            <Btn label="📷 Native Screenshot" onPress={this.captureScreenshot}/>
+            <Btn label="📷 Native Screenshot" onPress={this.snapshot()}/>
             <Btn
               label="📷 Empty View (should crash)"
               onPress={this.snapshot("empty")}