我的 android 應用程序在我的虛擬設備上運行，但不在我的物理 android 設備上

Question

我有問題，當我在虛擬設備上運行我的應用程序時一切正常，但是當我在我的物理手機上運行它時，在我按下按鈕應用程序崩潰后。 有時它會在屏幕上查看設備列表，但只有幾秒鍾，然后應用程序崩潰。

我發現有類似的問題，但它仍然不起作用。 我知道有時可能 arraylist 為空，但我不知道如何修復它。

我的代碼：

package com.example.drop_java_test2;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

import android.Manifest;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    Button scanBt;
    ListView scanList;
    ArrayList<String> devicesList = new ArrayList<String>();
    ArrayAdapter<String> arrayAdapter;

    BluetoothAdapter btAdapter = BluetoothAdapter.getDefaultAdapter();


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


        scanBt = (Button) findViewById(R.id.bt);
        scanList = (ListView) findViewById(R.id.list);

        ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.ACCESS_FINE_LOCATION, Manifest.permission.ACCESS_COARSE_LOCATION}, 1001); //Any number
        
        scanBt.setOnClickListener(new View.OnClickListener(){

            @Override
            public void onClick(View v){
                if(devicesList == null){
                    devicesList = new ArrayList<String>();
                }

                System.out.println("Status:"+ btAdapter.startDiscovery());
            }
        });

        IntentFilter intentFilter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
        registerReceiver(myReciver,intentFilter);

        arrayAdapter = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1,devicesList);
        scanList.setAdapter(arrayAdapter);


    }

    BroadcastReceiver myReciver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if(BluetoothDevice.ACTION_FOUND.equals(action)){
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                devicesList.add(device.getName());
                arrayAdapter.notifyDataSetChanged();
                System.out.println("Name:"+ device.getName()+ "\nAddress:"+ device.getAddress());
            }
        }

    };
}

XML：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/bt"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Scan"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <ListView
        android:id="@+id/list"
        android:layout_width="248dp"
        android:layout_height="417dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/bt" />

</androidx.constraintlayout.widget.ConstraintLayout>

日志：

2021-11-06 18:37:51.131 582-582/com.example.drop_java_test2 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.drop_java_test2, PID: 582
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
        at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:454)
        at android.widget.ArrayAdapter.getView(ArrayAdapter.java:416)
        at android.widget.AbsListView.obtainView(AbsListView.java:2424)
        at android.widget.ListView.makeAndAddView(ListView.java:2098)
        at android.widget.ListView.fillDown(ListView.java:813)
        at android.widget.ListView.fillSpecific(ListView.java:1524)
        at android.widget.ListView.originalLayoutChildren(ListView.java:1833)
        at android.widget.ListView.layoutChildren(ListView.java:1662)
        at android.widget.AbsListView.onLayout(AbsListView.java:2218)
        at android.view.View.layout(View.java:23058)
        at android.view.ViewGroup.layout(ViewGroup.java:6479)
        at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1873)
        at android.view.View.layout(View.java:23058)
        at android.view.ViewGroup.layout(ViewGroup.java:6479)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
        at android.view.View.layout(View.java:23058)
        at android.view.ViewGroup.layout(ViewGroup.java:6479)
        at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:536)
        at android.view.View.layout(View.java:23058)
        at android.view.ViewGroup.layout(ViewGroup.java:6479)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
        at android.view.View.layout(View.java:23058)
        at android.view.ViewGroup.layout(ViewGroup.java:6479)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
        at android.view.View.layout(View.java:23058)
        at android.view.ViewGroup.layout(ViewGroup.java:6479)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
        at com.android.internal.policy.DecorView.onLayout(DecorView.java:804)
        at android.view.View.layout(View.java:23058)
        at android.view.ViewGroup.layout(ViewGroup.java:6479)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3613)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:3073)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:2066)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8496)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1076)
        at android.view.Choreographer.doCallbacks(Choreographer.java:897)
        at android.view.Choreographer.doFrame(Choreographer.java:826)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1061)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:236)
        at android.app.ActivityThread.main(ActivityThread.java:8061)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:656)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:967)
2021-11-06 18:37:51.167 582-582/com.example.drop_java_test2 I/Process: Sending signal. PID: 582 SIG: 9

Answer 1

您假設device.getName()將始終返回String ，但有時它會返回null 。 我的猜測是您從getName()獲取null並將其放入您的ArrayList ，而這正是ArrayAdapter不喜歡的。 嘗試檢查null並跳過該藍牙設備或替換一些默認名稱。

此外， getApplicationContext()很少是 UI 事物的正確答案。 改用this來引用您的活動。

Answer 2

翻轉這兩行

registerReceiver(myReciver,intentFilter);

arrayAdapter = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1,devicesList);

當您調用 registerReceiver 時，有一行：

arrayAdapter.notifyDataSetChanged();

但是此時您的 arrayAdapter 尚未初始化。 所以它是空的。