Question

我想显示android蓝牙api发现的蓝牙设备列表，但我不知道为什么会出现这个错误：

FATAL EXCEPTION：main java.lang.RuntimeException：无法启动活动 ComponentInfo {com.example.fatma.listviewcst / com.example.fatma.listviewcst.MainActivity}：显示java.lang.NullPointerException

MainActivity.java

package com.example.fatma.listviewcst;

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.support.v7.app.AppCompatActivity;
import android.widget.ListView;
import android.widget.Toast;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
    ListView listView;
    BluetoothDev bluetoothDev;
    ArrayList<BluetoothDevice> mArrayAdapter ;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
       // setContentView(R.layout.activity_main);




        }

    @Override
    protected void onStart() {
        super.onStart();
       displayDiscovry();

    }

    public void  displayDiscovry(){
        BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        if (bluetoothAdapter == null) {
            Toast t = new Toast(this);
            t.setText("Sorry your phone do not support Bluetooth");
            t.show();
        } else {
            if (!bluetoothAdapter.isEnabled()) {
                Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
                startActivityForResult(enableBtIntent,1);}
            //   bluetoothDev=new BluetoothDev();

            //added
            // Create a BroadcastReceiver for ACTION_FOUND
            final BroadcastReceiver mReceiver = new BroadcastReceiver() {
                public void onReceive(Context context, Intent intent) {
                    String action = intent.getAction();
                    // When discovery finds a device
                    if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                        // Get the BluetoothDevice object from the Intent
                        BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                        // Add the name and address to an array adapter to show in a ListView
                        mArrayAdapter.add(device);
                    }
                }
            };
// Register the BroadcastReceiver
            IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
            registerReceiver(mReceiver, filter); // Don't forget to unregister during onDestroy
            //end added
            listView=(ListView)findViewById(R.id.listView);

            devList listeDev=new devList(this,R.layout.item,mArrayAdapter);
            listView.setAdapter(listeDev);}
    }
}

devList.java

package com.example.fatma.listviewcst;

import android.bluetooth.BluetoothDevice;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import java.util.List;

/**
 * Created by FATMA on 02/04/2016.
 */
public class devList extends ArrayAdapter<BluetoothDevice>{
    Context context;
    int resource;


    public devList(Context context, int resource, List<BluetoothDevice> bluetoothDev) {
        super(context, resource, bluetoothDev);
        this.context=context;
        this.resource=resource;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        //inflater charge le contenu d un fichier ds une vue
        LayoutInflater inflater =(LayoutInflater)context.getSystemService(context.LAYOUT_INFLATER_SERVICE);
        //false pour dire non pas attaché au root
        View view =inflater.inflate(resource,parent,false);
        TextView devName= (TextView) view.findViewById(R.id.devName);
        TextView devMac= (TextView) view.findViewById(R.id.devMac);

        devName.setText( getItem(position).getName());
        devMac.setText(getItem(position).getAddress());

        return view;
    }
}

list_view_item.xml

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical" android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/devName" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/devMac" />

    </LinearLayout>

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.fatma.listviewcst.MainActivity">

    <ListView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/listView"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />
</RelativeLayout>

Answer 1

编辑：这已被接受，但答案不正确。

问题是由mArrayAdapter在调用add之前未初始化造成的。

原帖

如果没有看到更多的堆栈跟踪，很难说出问题归结为什么。

但我建议您可能会因为注释掉代码setContentView(R.layout.activity_main);而导致这种情况。我建议这样做是因为只要您尝试连接到蓝牙以列出您调用listView=(ListView)findViewById(R.id.listView);的设备，但是没有根视图可以查找任何视图。

在列表视图中显示扫描蓝牙设备的结果

1 个答案:

原帖