How to Fix Android Logcat Filter Issues — Reading Debug Logs

In this tutorial, you'll learn about How to Fix Android Logcat Filter Issues. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

The Problem

Android Logcat shows no output or too much output:

No logs from the selected Process.

or logcat shows system messages but not your app's logs.

Quick Fix

Step 1: Create a package filter

WRONG — no filter:

Logcat shows all system messages (thousands of lines).

RIGHT — filter by package name:

logcat --pid=$(adb shell pidof -s com.example.myapp)

Or in Android Studio:

Select app from the dropdown > "Show only selected application"

Step 2: Use tag and priority filters

# Filter by tag and priority:
logcat -s MyApp:D     # only tag "MyApp" with debug and above
logcat *:W            # all tags, warning and above

Priority levels: V(erbose), D(ebug), I(nfo), W(arning), E(ror), F(atal).

Step 3: Log from your app effectively

WRONG:

Log.d("debug", "Button clicked");

RIGHT — use meaningful tags:

private static final String TAG = "LoginActivity";
Log.d(TAG, "User clicked login button");
Log.e(TAG, "Login failed: " + error.getMessage());

Step 4: Clear the log

adb logcat -c

Step 5: Save logs to a file

adb logcat -d > debug.log

Or from Android Studio:

Export icon (or right-click) > Export to file

Step 6: Filter by log level in Android Studio

Logcat panel > Level dropdown > Debug (or Error)

Prevention

• Always use a TAG constant in every class.
• Filter by package name in Android Studio.
• Use Log.w() and Log.e() for warnings and errors.

Common Mistakes with logcat filter

1. Forgetting deriving (Show, Eq) on custom data types needed for debugging
2. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable
3. Using head and tail instead of pattern matching, causing runtime errors on empty lists

These mistakes appear frequently in real-world Android code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ