Android topics — 21: חיישן תאוצה שהופך להטיה

 package com.example.topics;
 
+import android.hardware.Sensor;
+import android.hardware.SensorEvent;
+import android.hardware.SensorEventListener;
+import android.hardware.SensorManager;
 import android.os.Bundle;
-
 import androidx.activity.EdgeToEdge;
 import androidx.appcompat.app.AppCompatActivity;
 import androidx.core.graphics.Insets;
 import androidx.core.view.ViewCompat;
 import androidx.core.view.WindowInsetsCompat;
-
 import com.example.topics.databinding.ActivityMainBinding;
 
-public class MainActivity extends AppCompatActivity {
+public class MainActivity extends AppCompatActivity implements SensorEventListener {
+    private ActivityMainBinding binding;
+    private SensorManager sensors;
+    private Sensor accelerometer;
+    private final float[] gravity = new float[3];
+    private boolean initialized;
+    private long previousEventNs;
+    private long previousDisplayNs;
 
-    private ActivityMainBinding binding;
-
+    /**
+     * Creates the current Activity View tree and connects the screen's actions.
+     *
+     * @param savedInstanceState prior small UI snapshot, or null for a fresh launch
+     */
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
 ⁞
         setContentView(binding.getRoot());
         ViewCompat.setOnApplyWindowInsetsListener(binding.main, (v, insets) -> {
             Insets bars = insets.getInsets(WindowInsetsCompat.Type.systemBars() | WindowInsetsCompat.Type.displayCutout());
-            v.setPadding(bars.left, bars.top, bars.right, bars.bottom);            return insets;
+            v.setPadding(bars.left, bars.top, bars.right, bars.bottom);
+            return insets;
         });
+        sensors = getSystemService(SensorManager.class);
+        accelerometer = sensors.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
+        if (accelerometer == null) binding.reading.setText(R.string.no_sensor);
+    }
+
+    /**
+     * Starts a fresh estimate and registers only while this screen is active.
+     */
+    @Override
+    protected void onResume() {
+        super.onResume();
+        initialized = false;
+        previousEventNs = 0;
+        previousDisplayNs = 0;
+        if (accelerometer != null && !sensors.registerListener(this, accelerometer,
+                SensorManager.SENSOR_DELAY_UI)) binding.reading.setText(R.string.no_sensor);
+    }
+
+    /**
+     * Stops receiving samples before the screen becomes inactive.
+     */
+    @Override
+    protected void onPause() {
+        sensors.unregisterListener(this);
+        super.onPause();
+    }
+
+    /**
+     * Filters acceleration into a rough gravity estimate and displays a tilt at most 10 times/s.
+     * Linear movement can distort this estimate; it is not a precision orientation sensor.
+     *
+     * @param event acceleration in m/s squared with a monotonic nanosecond timestamp
+     */
+    @Override
+    public void onSensorChanged(SensorEvent event) {
+        if (event.sensor.getType() != Sensor.TYPE_ACCELEROMETER) return;
+        if (!initialized) {
+            // SensorEvent data can be reused; keep our own three-value estimate.
+            System.arraycopy(event.values, 0, gravity, 0, 3);
+            initialized = true;
+        } else {
+            for (int axis = 0; axis < 3; axis++) {
+                // Smooth every sample; the separate display throttle does not skip filtering.
+                gravity[axis] = 0.8f * gravity[axis] + 0.2f * event.values[axis];
+            }
+        }
+        long intervalMs = previousEventNs == 0 ? 0 : (event.timestamp - previousEventNs) / 1_000_000;
+        previousEventNs = event.timestamp;
+        // Nanoseconds measure sensor time, not wall-clock time.
+        if (event.timestamp - previousDisplayNs < 100_000_000L) return;
+        previousDisplayNs = event.timestamp;
+        double angle = Math.toDegrees(Math.atan2(gravity[0],
+                Math.hypot(gravity[1], gravity[2])));
+        binding.tilt.setProgress((int) Math.round(angle + 90));
+        binding.reading.setText(getString(R.string.sensor_reading, gravity[0], gravity[1],
+                gravity[2], angle, intervalMs));
+    }
+
+    /**
+     * Receives sensor accuracy changes; this demonstration has no calibration workflow.
+     *
+     * @param sensor sensor whose accuracy changed
+     * @param accuracy Android accuracy classification
+     */
+    @Override
+    public void onAccuracyChanged(Sensor sensor, int accuracy) {
+        // The demo uses the current reading; no calibration UI is needed here.
     }
 }

     android:layout_width="match_parent"
     android:layout_height="match_parent"
     tools:context=".MainActivity">
-
-    <TextView
-        android:layout_width="wrap_content"
+    <LinearLayout
+        android:layout_width="0dp"
         android:layout_height="wrap_content"
-        android:text="Hello World!"
-        app:layout_constraintBottom_toBottomOf="parent"
-        app:layout_constraintEnd_toEndOf="parent"
+        android:orientation="vertical"
+        android:padding="24dp"
+        app:layout_constraintTop_toTopOf="parent"
         app:layout_constraintStart_toStartOf="parent"
-        app:layout_constraintTop_toTopOf="parent" />
-
+        app:layout_constraintEnd_toEndOf="parent">
+        <TextView
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:text="@string/sensor_intro"
+            android:textSize="20sp" />
+        <ProgressBar
+            android:id="@+id/tilt"
+            style="?android:attr/progressBarStyleHorizontal"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="24dp"
+            android:max="180"
+            android:progress="90" />
+        <TextView
+            android:id="@+id/reading"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="16dp"
+            android:text="@string/waiting_sensor"
+            android:textSize="18sp" />
+    </LinearLayout>
 </androidx.constraintlayout.widget.ConstraintLayout>

 <resources>
     <string name="app_name">topics</string>
+    <string name="sensor_intro">Tilt the phone sideways. The bar shows the filtered X-axis gravity angle.</string>
+    <string name="waiting_sensor">Waiting for accelerometer readings…</string>
+    <string name="no_sensor">This device has no accelerometer.</string>
+    <string name="sensor_reading">Gravity estimate X=%1$.2f, Y=%2$.2f, Z=%3$.2f m/s²; sideways tilt=%4$.0f°; sample interval=%5$d ms.</string>
 </resources>