Sample, add block handler sample

app-sample/samples.json

@@ -1,4 +1,16 @@
 [
+  {
+    "javaClassName": "io.noties.markwon.app.samples.BlockHandlerSample",
+    "id": "202007211090524",
+    "title": "Block handler",
+    "description": "Custom block delimiters that control new lines after block nodes",
+    "artifacts": [
+      "CORE"
+    ],
+    "tags": [
+      "rendering"
+    ]
+  },
   {
     "javaClassName": "io.noties.markwon.app.samples.CacheMarkwonSample",
     "id": "202007189102458",

app-sample/src/main/java/io/noties/markwon/app/samples/BlockHandlerSample.java

@@ -0,0 +1,66 @@
+package io.noties.markwon.app.samples;
+
+import androidx.annotation.NonNull;
+
+import org.commonmark.node.Node;
+
+import io.noties.markwon.AbstractMarkwonPlugin;
+import io.noties.markwon.Markwon;
+import io.noties.markwon.MarkwonVisitor;
+import io.noties.markwon.app.sample.Tags;
+import io.noties.markwon.app.sample.ui.MarkwonTextViewSample;
+import io.noties.markwon.sample.annotations.MarkwonArtifact;
+import io.noties.markwon.sample.annotations.MarkwonSampleInfo;
+
+@MarkwonSampleInfo(
+  id = "202007211090524",
+  title = "Block handler",
+  description = "Custom block delimiters that control new lines after block nodes",
+  artifacts = MarkwonArtifact.CORE,
+  tags = Tags.rendering
+)
+public class BlockHandlerSample extends MarkwonTextViewSample {
+  @Override
+  public void render() {
+    final String md = "" +
+      "# Heading\n" +
+      "* one\n" +
+      "* two\n" +
+      "* three\n" +
+      "---\n" +
+      "> a quote\n\n" +
+      "```\n" +
+      "code\n" +
+      "```\n" +
+      "some text after";
+
+    final Markwon markwon = Markwon.builder(context)
+      .usePlugin(new AbstractMarkwonPlugin() {
+        @Override
+        public void configureVisitor(@NonNull MarkwonVisitor.Builder builder) {
+          builder.blockHandler(new BlockHandlerNoAdditionalNewLines());
+        }
+      })
+      .build();
+
+    markwon.setMarkdown(textView, md);
+  }
+}
+
+class BlockHandlerNoAdditionalNewLines implements MarkwonVisitor.BlockHandler {
+
+  @Override
+  public void blockStart(@NonNull MarkwonVisitor visitor, @NonNull Node node) {
+    // ensure that content rendered on a new line
+    visitor.ensureNewLine();
+  }
+
+  @Override
+  public void blockEnd(@NonNull MarkwonVisitor visitor, @NonNull Node node) {
+    if (visitor.hasNext(node)) {
+      visitor.ensureNewLine();
+      // by default markwon here also has:
+      //  visitor.forceNewLine();
+    }
+  }
+}