Question

我编写了以下代码，其中包含清单文件中包含的权限。

package com.cognism.device;
import java.io.IOException;
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.content.Context; 
import android.content.Intent; 
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView; 
import android.widget.Toast; 

public class Trial extends Activity {

    // Declare our Views, so we can access them later   
    private Button activate_buletooth;
    static final int REQUEST_ENABLE_BT = 0;   
    Intent discoverableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
    BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();  


    /** Called when the activity is first created. */ 

    @Override     public void onCreate(Bundle savedInstanceState)

    {         super.onCreate(savedInstanceState);          
    // Set Activity Layout    
    setContentView(R.layout.main);       
    activate_buletooth = (Button)findViewById(R.id.activate_buletooth); 
    // Set Click Listener          
    activate_buletooth.setOnClickListener(new OnClickListener()
    {          @Override        
        public void onClick(View v)

    {      
        if (mBluetoothAdapter == null) 

    {               // Device does not support Bluetooth 
        Context context = getApplicationContext();  
        CharSequence text = "BT not suported";    
        int duration = Toast.LENGTH_SHORT;       
        Toast toast = Toast.makeText(context, text, duration);  
        toast.show();          
        }                
    if (!mBluetoothAdapter.isEnabled())
    {             
        Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE); 
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);     
        }           
    // startActivityForResult(discoverableIntent, REQUEST_ENABLE_BT);  
    }         
    });     
    }    
    @Override    
    protected void onActivityResult(int requestCode, int resultCode, Intent data) 
    {      if(requestCode == REQUEST_ENABLE_BT)     
    {       if(resultCode == RESULT_CANCELED)    
    {        Context context = getApplicationContext(); 
    CharSequence text = "bt not available";    
    int duration = Toast.LENGTH_SHORT;       
    Toast toast = Toast.makeText(context, text, duration);   
    toast.show();        
    }        
    else     
    {          

    }      
    }    
    } 




}

我一直在异常，DDM显示这些错误：

04-18 11:48:03.587: ERROR/AndroidRuntime(616): FATAL EXCEPTION: main
04-18 11:48:03.587: ERROR/AndroidRuntime(616): java.lang.NullPointerException
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at com.cognism.device.Trial$1.onClick(Trial.java:47)
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at android.view.View.performClick(View.java:2485)
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at android.view.View$PerformClick.run(View.java:9080)
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at android.os.Handler.handleCallback(Handler.java:587)
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at android.os.Handler.dispatchMessage(Handler.java:92)
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at android.os.Looper.loop(Looper.java:123)
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at android.app.ActivityThread.main(ActivityThread.java:3647)
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at java.lang.reflect.Method.invokeNative(Native Method)
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at java.lang.reflect.Method.invoke(Method.java:507)
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-18 11:48:03.587: ERROR/AndroidRuntime(616):     at dalvik.system.NativeStart.main(Native Method)
04-18 11:48:03.608: WARN/ActivityManager(61):   Force finishing activity com.cognism.device/.Trial
04-18 11:48:04.127: WARN/ActivityManager(61): Activity pause timeout for HistoryRecord{40683988 com.cognism.device/.Trial}
04-18 11:48:06.248: INFO/Process(616): Sending signal. PID: 616 SIG: 9
04-18 11:48:06.267: INFO/ActivityManager(61): Process com.cognism.device (pid 616) has died.
04-18 11:48:06.278: INFO/WindowManager(61): WIN DEATH: Window{4074aa58 com.cognism.device/com.cognism.device.Trial paused=false}
04-18 11:48:10.397: DEBUG/dalvikvm(429): GC_EXPLICIT freed 7K, 55% free 2519K/5511K, external 716K/1038K, paused 59ms
04-18 11:48:15.290: WARN/ActivityManager(61): Activity destroy timeout for HistoryRecord{40683988 com.cognism.device/.Trial}
04-18 11:48:15.457: DEBUG/dalvikvm(446): GC_EXPLICIT freed 20K, 55% free 2577K/5703K, external 716K/1038K, paused 98ms
04-18 11:48:20.458: DEBUG/dalvikvm(536): GC_EXPLICIT freed 55K, 49% free 3054K/5959K, external 716K/1038K, paused 57ms
04-18 11:48:25.508: DEBUG/dalvikvm(488): GC_EXPLICIT freed 6K, 55% free 2527K/5511K, external 716K/1038K, paused 82ms
04-18 11:51:59.923: DEBUG/SntpClient(61): request time failed: java.net.SocketException: Address family not supported by protocol
04-18 11:55:00.207: DEBUG/dalvikvm(61): GC_CONCURRENT freed 834K, 46% free 4391K/8007K, external 2050K/2558K, paused 7ms+8ms
04-18 11:56:59.967: DEBUG/SntpClient(61): request time failed: java.net.SocketException: Address family not supported by protocol

Answer 1

if (mBluetoothAdapter == null) 
{
  .... // code does not use "return"
}                
if (!mBluetoothAdapter.isEnabled()) // crash here if mBluetoothAdapter == null
{

这是你的onclick代码不正确。如果适配器为null，则第二个if将崩溃。

尝试：

if (mBluetoothAdapter == null) 
{
  .... 
}                
else if (!mBluetoothAdapter.isEnabled())
{

另外，判断这是一个快速的谷歌，mBluetoothAdapter应该在onCreate内而不是在类范围内初始化。

Answer 2

您好请遵循以下代码进行蓝牙激活： -

public class BluetoothDemo extends Activity {
  TextView out;

  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

        out = (TextView) findViewById(R.id.out);

    // Getting the Bluetooth adapter
    BluetoothAdapter adapter = BluetoothAdapter.getDefaultAdapter();
    out.append("\nAdapter: " + adapter);

    // Check for Bluetooth support in the first place 
    // Emulator doesn't support Bluetooth and will return null
    if(adapter==null) { 
      out.append("\nBluetooth NOT supported. Aborting.");
      return;
    }

    // Starting the device discovery
    out.append("\nStarting discovery...");
    adapter.startDiscovery();
    out.append("\nDone with discovery...");

    // Listing paired devices
    out.append("\nDevices Pared:");
    Set<BluetoothDevice> devices = adapter.getBondedDevices();
    for (BluetoothDevice device : devices) {
      out.append("\nFound device: " + device);
    }
  }
}

并且不要忘记在清单文件中提供这个...

<uses-permission android:name="android.permission.BLUETOOTH" />
  <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />

Answer 3

我遇到了完全相同的问题。原来你需要蓝牙和蓝牙管理员权限。仅凭管理员是不够的。

Answer 4

我有完全相同的问题。每次使用我的“bluetoothAdapter”都会导致应用程序崩溃，直到我在清单文件中添加了“<uses-permission …>”标记，如下所示：

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="charles.software"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".VitaleReader"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>



<uses-permission android:name="android.permission.BLUETOOTH" /> 
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" /> 
</manifest>

请注意文件末尾添加的两行，就在“</manifest>”标记之前。

现在可行。

激活蓝牙时例外

4 个答案: