private void setupDrawing() {
    drawPaint = new Paint();
    drawPaint.setColor(paintColor);
    drawPaint.setAntiAlias(true);
    drawPaint.setStrokeWidth(20);
    drawPaint.setStyle(Paint.Style.STROKE);
    drawPaint.setStrokeJoin(Paint.Join.ROUND);
    drawPaint.setStrokeCap(Paint.Cap.ROUND);
    canvasPaint = new Paint(Paint.DITHER_FLAG);
}

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
    drawCanvas = new Canvas(canvasBitmap);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    float touchX = event.getX();
    float touchY = event.getY();
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            drawPath.moveTo(touchX, touchY);
            break;
        case MotionEvent.ACTION_MOVE:
            drawPath.lineTo(touchX, touchY);
            break;
        case MotionEvent.ACTION_UP:
            drawCanvas.drawPath(drawPath, drawPaint);
            drawPath.reset();
            break;
        default:
            return false;
    }
    invalidate();
    return true;
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    signatureView = findViewById(R.id.signature_view);
    clearButton = findViewById(R.id.clear_button);
    saveButton = findViewById(R.id.save_button);
    shareButton = findViewById(R.id.share_button);
    
    clearButton.setOnClickListener(v -> signatureView.clear());
    saveButton.setOnClickListener(v -> saveSignature());
    shareButton.setOnClickListener(v -> shareSignature());
}

private void saveSignature() {
    Bitmap signatureBitmap = signatureView.getSignatureBitmap();
    if (isBitmapEmpty(signatureBitmap)) {
        Toast.makeText(this, "簽名為空，無(wú)法保存", Toast.LENGTH_SHORT).show();
        return;
    }
    try {
        File photoFile = createImageFile();
        try (FileOutputStream fos = new FileOutputStream(photoFile)) {
            signatureBitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
            Toast.makeText(this, "簽名已保存至相冊(cè)", Toast.LENGTH_SHORT).show();
        }
    } catch (IOException e) {
        e.printStackTrace();
        Toast.makeText(this, "保存失敗，請(qǐng)稍后再試", Toast.LENGTH_SHORT).show();
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp">
    
    <com.example.signatureapp.SignatureView
        android:id="@+id/signature_view"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:background="@android:color/white"
        android:layout_marginBottom="16dp"/>
        
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:weightSum="3">
        
        <Button
            android:id="@+id/clear_button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="清除"
            android:layout_marginRight="8dp"/>
            
        <Button
            android:id="@+id/save_button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="保存"
            android:layout_marginRight="8dp"/>
            
        <Button
            android:id="@+id/share_button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="分享"/>
    </LinearLayout>
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-files-path name="my_images" path="Pictures" />
</paths>

float pressure = event.getPressure();
drawPaint.setStrokeWidth(BASE_WIDTH + pressure * PRESSURE_FACTOR);

SecretKey secretKey = KeyGenerator.getInstance("AES").generateKey();
Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
cipher.init(Cipher.ENCRYPT_MODE, secretKey);
try (CipherOutputStream cos = new CipherOutputStream(fos, cipher)) {
    bitmap.compress(Bitmap.CompressFormat.PNG, 100, cos);
}