android如何在拔出USB时及时清除读取的数据缓存

Android中清除读取的数据缓存通常有两种方式：

1. 使用广播监听USB状态

可以注册一个广播接收器监听USB状态，当拔出USB时就清除缓存数据。

public class UsbDetectReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        final String action = intent.getAction();

        if (UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action)) {
            // USB拔出时清除数据缓存
            clearCacheData(context);
        }
    }

    private void clearCacheData(Context context) {
        // 清除数据缓存的逻辑代码
    }
}

然后在MainActivity中注册广播接收器：

public class MainActivity extends AppCompatActivity {

    private UsbDetectReceiver mUsbDetectReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 注册USB广播接收器
        mUsbDetectReceiver = new UsbDetectReceiver();
        IntentFilter intentFilter = new IntentFilter(UsbManager.ACTION_USB_DEVICE_DETACHED);
        registerReceiver(mUsbDetectReceiver, intentFilter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        // 解除广播接收器注册
        unregisterReceiver(mUsbDetectReceiver);
    }
}

2. 在Activity生命周期中使用onPause()方法清除数据缓存

在Activity的生命周期onPause()方法中检测是否拔出USB，如果已拔出就清除数据缓存。

public class MainActivity extends AppCompatActivity {

    private boolean mIsUsbConnected = false;

    @Override
    protected void onPause() {
        super.onPause();

        if (mIsUsbConnected) {
            // USB拔出时清除数据缓存
            clearCacheData();
            mIsUsbConnected = false;
        }
    }

    private void clearCacheData() {
        // 清除数据缓存的逻辑代码
    }
}

可以在OnResume()方法中检测USB连接状态并设置mIsUsbConnected变量：

public class MainActivity extends AppCompatActivity {

    private boolean mIsUsbConnected = false;

    @Override
    protected void onResume() {
        super.onResume();

        UsbManager usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
        HashMap<String, UsbDevice> deviceList = usbManager.getDeviceList();
        if (!deviceList.isEmpty()) {
            mIsUsbConnected = true;
        }
    }

    ...
}