java - 应用程序不断崩溃
问题描述
我是一个初学者 android 应用程序用户。我正在尝试根据在线示例制作 BLE 扫描仪。但是我的应用程序不断崩溃并且根本无法正常工作。谁能帮我确定问题？
我研究了各种在线解决方案。我下面的例子是这样的：
https ://github.com/kaviles/BLE_Tutorials
this is my manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.ble_scanner">
<uses-permission android:name="android.permission.BLUETOOTH"/>
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
这是我的主要活动：
public class MainActivity extends AppCompatActivity implements View.OnClickListener, AdapterView.OnItemClickListener {
private final static String TAG = MainActivity.class.getSimpleName();
public static final int REQUEST_ENABLE_BT = 1;
private HashMap<String, BTLE_Device> mBTDevicesHashMap;
private ArrayList<BTLE_Device> mBTDevicesArrayList;
private ListAdapter_BTLE_Devices adapter;
private Button btn_Scan;
private BroadcastReceiver_BTState mBTStateUpdateReceiver;
private Scanner_BTLE mBTLeScanner;
private static final int MY_PERMISSIONS_REQUEST_LOCATION = 99;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
checkLocationPermission();
if(!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)){
Utils.toast(getApplicationContext(),"BLE not supported");
finish();
}
mBTStateUpdateReceiver = new BroadcastReceiver_BTState(getApplicationContext());
mBTLeScanner = new Scanner_BTLE(this,7500,-75);
mBTDevicesHashMap = new HashMap<>();
mBTDevicesArrayList = new ArrayList<>();
adapter = new ListAdapter_BTLE_Devices(this, R.layout.btle_device_list_item, mBTDevicesArrayList);
ListView listView = new ListView(this);
listView.setAdapter(adapter);
listView.setOnItemClickListener(this);
btn_Scan = (Button) findViewById(R.id.btn_scan);
((ScrollView) findViewById(R.id.scrollView)).addView(listView);
findViewById(R.id.btn_scan).setOnClickListener(this);
}
@Override
protected void onStart(){
super.onStart();
registerReceiver(mBTStateUpdateReceiver, new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED));
}
@Override
protected void onResume(){
super.onResume();
}
@Override
protected void onPause(){
super.onPause();
stopScan();
}
protected void onStop(){
super.onStop();
unregisterReceiver(mBTStateUpdateReceiver);
startScan();
}
@Override
protected void onDestroy(){
super.onDestroy();
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data){
if (requestCode == REQUEST_ENABLE_BT){
if (resultCode == RESULT_OK){
Utils.toast(getApplicationContext(),"Bluetooth is ready to use");
}
else if (resultCode == RESULT_CANCELED){
Utils.toast(getApplicationContext(),"Please turn on Bluetooth");
}
}
}
@Override
public void onClick(View v) {
switch (v.getId()){
case R.id.btn_scan:
Utils.toast(getApplicationContext(),"Scan button pressed");
if(!mBTLeScanner.isScanning()){
startScan();
} else {
startScan();
}
break;
default:
break;
}
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
}
public void addDevice(BluetoothDevice device, int new_rssi) {
String address = device.getAddress();
if(!mBTDevicesHashMap.containsKey(address)){
BTLE_Device btle_device = new BTLE_Device(device);
btle_device.setRssi(new_rssi);
mBTDevicesHashMap.put(address, btle_device);
mBTDevicesArrayList.add(btle_device);
} else {
mBTDevicesHashMap.get(address).setRssi(new_rssi);
}
adapter.notifyDataSetChanged();
}
public void startScan(){
btn_Scan.setText("Scanning...");
mBTDevicesArrayList.clear();
mBTDevicesHashMap.clear();
adapter.notifyDataSetChanged();
mBTLeScanner.start();
}
public void stopScan() {
btn_Scan.setText("Scan Again");
mBTLeScanner.stop();
}
public boolean checkLocationPermission() {
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
!= PackageManager.PERMISSION_GRANTED) {
// Should we show an explanation?
if (ActivityCompat.shouldShowRequestPermissionRationale(this,
Manifest.permission.ACCESS_FINE_LOCATION)) {
// Show an explanation to the user *asynchronously* -- don't block
// this thread waiting for the user's response! After the user
// sees the explanation, try again to request the permission.
new AlertDialog.Builder(this)
.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
//Prompt the user once explanation has been shown
ActivityCompat.requestPermissions(MainActivity.this,
new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
MY_PERMISSIONS_REQUEST_LOCATION);
}
})
.create()
.show();
} else {
// No explanation needed, we can request the permission.
ActivityCompat.requestPermissions(this,
new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
MY_PERMISSIONS_REQUEST_LOCATION);
}
return false;
} else {
return true;
}
}
@Override
public void onRequestPermissionsResult(int requestCode,
String permissions[], int[] grantResults) {
switch (requestCode) {
case MY_PERMISSIONS_REQUEST_LOCATION: {
// If request is cancelled, the result arrays are empty.
if (grantResults.length > 0
&& grantResults[0] == PackageManager.PERMISSION_GRANTED) {
// permission was granted, yay! Do the
// location-related task you need to do.
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
onResume();
}
} else {
onDestroy();
}
return;
}
}
}
}
这是日志猫：
2019-07-16 14:45:14.758 26071-26071/com.example.ble_scanner I/ple.ble_scanne: Not late-enabling -Xcheck:jni (already on)
2019-07-16 14:45:14.837 26071-26071/com.example.ble_scanner W/ple.ble_scanne: Unexpected CPU variant for X86 using defaults: x86
2019-07-16 14:45:14.935 26071-26079/com.example.ble_scanner E/ple.ble_scanne: Failed to send DDMS packet REAQ to debugger (-1 of 20): Broken pipe
2019-07-16 14:45:15.164 26071-26071/com.example.ble_scanner W/ple.ble_scanne: JIT profile information will not be recorded: profile file does not exits.
2019-07-16 14:45:15.166 26071-26071/com.example.ble_scanner I/chatty: uid=10096(com.example.ble_scanner) identical 10 lines
2019-07-16 14:45:15.166 26071-26071/com.example.ble_scanner W/ple.ble_scanne: JIT profile information will not be recorded: profile file does not exits.
2019-07-16 14:45:15.215 26071-26071/com.example.ble_scanner I/InstantRun: starting instant run server: is main process
2019-07-16 14:45:15.610 26071-26071/com.example.ble_scanner W/ple.ble_scanne: Accessing hidden method Landroid/view/View;->computeFitSystemWindows(Landroid/graphics/Rect;Landroid/graphics/Rect;)Z (light greylist, reflection)
2019-07-16 14:45:15.612 26071-26071/com.example.ble_scanner W/ple.ble_scanne: Accessing hidden method Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (light greylist, reflection)
2019-07-16 14:45:15.824 26071-26071/com.example.ble_scanner E/BluetoothAdapter: Bluetooth binder is null
2019-07-16 14:45:15.831 26071-26071/com.example.ble_scanner D/AndroidRuntime: Shutting down VM
2019-07-16 14:45:15.834 26071-26071/com.example.ble_scanner E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.ble_scanner, PID: 26071
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ble_scanner/com.example.ble_scanner.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ScrollView.addView(android.view.View)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ScrollView.addView(android.view.View)' on a null object reference
at com.example.ble_scanner.MainActivity.onCreate(MainActivity.java:65)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
解决方案
在您的 xml 布局中尝试检查 ScrollView 的 id 是否为“ scrollView ”，如果没有将其更改为scrollView，则与您在这一行中的初始化方式相同。
((ScrollView) findViewById(R.id.scrollView)).addView(listView);
或者如果存在 ScrollView 小部件，请检查您的 xml 布局。它抛出空指针异常，因为它无法绑定布局，id 可能拼写错误或布局中没有滚动视图小部件。
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