android: add folder picker

android/app/src/main/java/com/logseq/app/FolderPicker.java

@@ -0,0 +1,33 @@
+package com.logseq.app;
+
+import android.content.Intent;
+
+import androidx.activity.result.ActivityResult;
+
+import com.getcapacitor.JSObject;
+import com.getcapacitor.Plugin;
+import com.getcapacitor.annotation.ActivityCallback;
+import com.getcapacitor.annotation.CapacitorPlugin;
+import com.getcapacitor.PluginCall;
+import com.getcapacitor.PluginMethod;
+
+
+@CapacitorPlugin(name = "FolderPicker")
+public class FolderPicker extends Plugin {
+    @PluginMethod()
+    public void pickFolder(PluginCall call) {
+        Intent i = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
+        i.addCategory(Intent.CATEGORY_DEFAULT);
+        startActivityForResult(call, i, "folderPickerResult");
+    }
+
+    @ActivityCallback
+    private void folderPickerResult(PluginCall call, ActivityResult result) {
+        if (call == null) {
+            return;
+        }
+        JSObject ret = new JSObject();
+        ret.put("result", result.getData().getData());
+        call.resolve(ret);
+    }
+}

android/app/src/main/java/com/logseq/app/MainActivity.java

@@ -1,5 +1,13 @@
 package com.logseq.app;
 
+import android.os.Bundle;
+
 import com.getcapacitor.BridgeActivity;
 
-public class MainActivity extends BridgeActivity {}
+public class MainActivity extends BridgeActivity {
+    @Override
+    public void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        registerPlugin(FolderPicker.class);
+    }
+}