안드로이드 앱 만들기 #3 (Intent 화면전환) - 쉽게 앱 만드는 방법 (현직 개발자 설명) , android studio easy tutorial

Main focus / concepts covered

This tutorial demonstrates how to navigate between Activities (screens) in an Android app using Intents and how to pass data between them.

Key concepts:

• What an Intent is: the mechanism to navigate between Activities.
• Creating a second Activity (SubActivity) and its layout XML so you can move from Activity A → Activity B.
• Wiring UI elements in XML (Button, EditText, TextView), assigning IDs, and connecting them in Java with findViewById.
• Handling clicks with OnClickListener to trigger navigation.
• Creating and using an Intent:
  • new Intent(CurrentActivity.this, SubActivity.class)
  • startActivity(intent)
• Passing data between Activities:
  • Put data into the Intent before starting: intent.putExtra("key", value) (e.g., a String from an EditText).
  • Receive data in the destination Activity: getIntent().getStringExtra("key") (or other getXExtra variants) and set it into a TextView.
• Common Android details and gotchas:
  • Always end Java statements with semicolons.
  • Use Alt+Enter or auto-complete to add imports if needed.
  • Lifecycle/timing bug: do not capture EditText text at app startup if you want the user’s later input — read the EditText and call putExtra inside the button’s click handler so current input is sent.
  • If sending numeric types, convert appropriately (e.g., putExtra / getIntExtra).

Running and testing:

• Build and run on a physical Android device or an emulator to verify navigation and data passing.
• This pattern (Intent + putExtra / getIntent) is widely used and practical in real apps.

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Step-by-step guide (high-level)

1. Create a project and add a new Activity (e.g., SubActivity) via New → Activity.
2. Edit layout XMLs:
   • Use a LinearLayout.
   • Add an EditText for input, a Button (Move), and a TextView to show received text.

3. In MainActivity.java:

   • Declare and initialize UI references: java EditText editText = findViewById(R.id.xxx); Button btnMove = findViewById(R.id.xxx);

   • In btnMove.setOnClickListener: java btnMove.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { String text = editText.getText().toString(); Intent i = new Intent(MainActivity.this, SubActivity.class); i.putExtra("sdr", text); startActivity(i); } });

4. In SubActivity.java: java TextView tvSub = findViewById(R.id.tv_sub); String s = getIntent().getStringExtra("sdr"); tvSub.setText(s);

5. Fix lifecycle issues by ensuring data is fetched and put into the Intent at the moment the user clicks the button (not at app startup).

Tip: always call editText.getText().toString() inside the click handler so you send the current input.

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Troubleshooting tips

• If text isn’t passed, check that you call editText.getText().toString() inside the click handler before creating/starting the Intent.
• Verify IDs in XML match those used in findViewById().
• Use auto-import (Alt+Enter) for missing imports.
• Watch the logcat and run on an emulator/device to confirm behavior.

Lifecycle/timing bug: do not capture EditText text at startup; read it and call putExtra inside the button’s click handler so the user’s current input is sent.

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Additional notes

• Instructor briefly mentions UI tweaks (text size using sp), layout choices (e.g., LinearLayout), and project/theme settings.
• There is an offline chat/Q&A available (per instructor) for follow-up questions.

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Main speaker / source

• Hoeung Druid (현직 개발자)