Android:添加 ScanCallback 让我 "Unfortunately, App has stopped."找不到 MainActivity

Question

我是 android 开发的新手。我看过一些 youtube 视频并阅读了一些文档。今天就像第 5 天，所以请耐心等待我。我正在尝试构建一个 BluetoothLE 应用程序。我从 here 偷了一些代码，但是当我尝试在我的设备上运行时。我收到一条消息“不幸的是，(应用程序名称)已停止”。在注释掉不同的代码块后，我将其固定到声明中:

private ScanCallback mScanCallback = new ScanCallback() {};

如果我包含该行，它就会崩溃。如果我不这样做，它就会活着。这是完整的 Java 类:

package com.tremor.creech.bluetoothExample;

import android.annotation.TargetApi;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothGatt;
import android.bluetooth.le.BluetoothLeScanner;
import android.bluetooth.le.ScanCallback;
import android.bluetooth.le.ScanFilter;
import android.bluetooth.le.ScanSettings;
import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;

import java.util.List;
@TargetApi(21)
public class MainActivity extends AppCompatActivity {

    private BluetoothAdapter mBluetoothAdapter;
    private int REQUEST_ENABLE_BT = 1;
    private Handler mHandler;
    private static final long SCAN_PERIOD = 10000;
    private BluetoothLeScanner mLEScanner;
    private ScanSettings settings;
    private List<ScanFilter> filters;
    private BluetoothGatt mGatt;

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

    private ScanCallback mScanCallback = new ScanCallback() { }; //If I include this line, then it crashes. If I take it out, then I see my Hello World activity.
}

LogCat 错误:

09-15 19:16:17.503    1878-1878/com.roberts.croberts.mantis E/dalvikvm﹕ Could not find class 'com.roberts.croberts.mantis.MainActivity$1', referenced from method com.roberts.croberts.mantis.MainActivity.<init>
09-15 19:16:17.523    1878-1878/com.roberts.croberts.mantis E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.roberts.croberts.mantis, PID: 1878
    java.lang.NoClassDefFoundError: com.roberts.croberts.mantis.MainActivity$1
            at com.roberts.croberts.mantis.MainActivity.<init>(MainActivity.java:154)
            at java.lang.Class.newInstanceImpl(Native Method)
            at java.lang.Class.newInstance(Class.java:1208)
            at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2119)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2252)
            at android.app.ActivityThread.access$800(ActivityThread.java:139)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1200)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5103)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:606)
            at dalvik.system.NativeStart.main(Native Method)
09-15 19:16:18.023      461-717/? E/Diag_Lib﹕ Thread state: conn_id=0, state=RX_THREAD_WAIT_READ
09-15 19:16:18.023      461-717/? E/Diag_Lib﹕ Thread state: conn_id=0, state=RX_THREAD_CLIENT_TX
09-15 19:16:18.023      461-717/? E/Diag_Lib﹕ qmi_qmux: TX/RX - RX 30 bytes on conn_id=0
09-15 19:16:18.023      461-717/? E/Diag_Lib﹕ 01 1D 00 80 03 01 04 00 00 51 00 11 00 10 03 00
09-15 19:16:18.023      461-717/? E/Diag_Lib﹕ BA 0E 00 11 08 00 BE 08 00 07 00 00 00 00
09-15 19:16:18.023      461-717/? E/Diag_Lib﹕ qmuxd: TX message on fd=29, to qmux_client_id=2, len=64
09-15 19:16:18.023      461-717/? E/Diag_Lib﹕ Thread state: conn_id=0, state=RX_THREAD_WAIT_POLL
09-15 19:16:18.033      454-454/? E/Parcel﹕ Reading a NULL string not supported here.
09-15 19:16:18.033      454-454/? E/Parcel﹕ Reading a NULL string not supported here.
09-15 19:16:18.033      454-454/? E/Parcel﹕ Reading a NULL string not supported here.
09-15 19:16:18.033      454-454/? E/Parcel﹕ Reading a NULL string not supported here.

Answer 1

不幸的是，要在 android 下构建 BLE 应用程序，您必须将 android Jelly Bean MR2(18) + Kitkat(19) 和 Lollipop (21+) 分开。

因为你才刚刚开始，所以我给你一个大概的检查方法。

首先为 JellyBean/Kitkat 声明这些变量和 lollipop .

//For Jelly Bean MR2 and Kitkat
private BluetoothAdapter.LeScanCallback leScanCallback;

//For Lollipop.
private BluetoothLeScanner bluetoothLeScanner;
private ScanCallback scanCallback;

由于它们未启动，因此运行该应用程序时不会出现错误。为了启动目标 api 是什么，您可以使用 Build :

if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
    //JellyBean/Kitkat
} else {
    //lollipop+
}

另外不要忘记检查手机是否真的具有 Ble 功能，是否需要在 list 中使用 uses 功能:

<uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>

并从 PackageManager 检查:

boolean hasBle = getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE);

必须执行此检查，因为某些手机(如 galaxy nexus)可以使用 jelly bean MR2，但没有 BLE 功能)

最后的建议，要非常小心回调泄漏并正确停止/删除回调；)