这是练习蓝牙基础知识的简单代码。 我在其中添加了这些功能 开启，关闭，配对设备和搜索设备。
但是，一旦我点击运行它就会显示这些错误
MainActivity.java
public class MainActivity extends Activity {
private static final int ENABLE_BT=1;
Button btnOn, btnOff, btnPaired, btnSearch;
ListView listView;
BluetoothAdapter bluetoothAdapter;
TextView textStatus;
Set<BluetoothDevice> bluetooDevice;
ArrayAdapter<String> madapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnOn= (Button) findViewById(R.id.buttonOn);
btnOff = (Button) findViewById(R.id.buttonOff);
btnPaired = (Button) findViewById(R.id.buttonPaired);
btnSearch = (Button) findViewById(R.id.buttonSearch);
textStatus = (TextView) findViewById(R.id.textUpdateStatus);
bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
if(bluetoothAdapter == null){
btnOn.setEnabled(false);
btnOff.setEnabled(false);
btnPaired.setEnabled(false);
btnSearch.setEnabled(false);
textStatus.setText("Not Supported");
Toast.makeText(getBaseContext(), "Your Device Does not Support Bluetooth", Toast.LENGTH_SHORT).show();
}
else{
btnOn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
on(arg0);
}
});
btnOff.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
});
btnPaired.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
pairedDevice(v);
}
});
btnSearch.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
search(v);
}
});
}
madapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1);
listView.setAdapter(madapter);
}
public void on(View v){
if(!bluetoothAdapter.isEnabled()){
Intent turnOn = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(turnOn, ENABLE_BT);
Toast.makeText(getApplicationContext(), "Bluetooth Turned On", Toast.LENGTH_SHORT).show();
}
else{
Toast.makeText(getApplicationContext(), "Bluetooth is aleady on", Toast.LENGTH_SHORT).show();
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// TODO Auto-generated method stub
super.onActivityResult(requestCode, resultCode, data);
if(requestCode == ENABLE_BT){
if(bluetoothAdapter.isEnabled()){
textStatus.setText("Enabled");
}
else{
textStatus.setText("Disabled");
}
}
}
public void pairedDevice(View v ){
bluetooDevice = bluetoothAdapter.getBondedDevices();
for(BluetoothDevice device : bluetooDevice){
madapter.add(device.getName()+"\n"+device.getAddress());
Toast.makeText(getApplicationContext(), "Paired Devices", Toast.LENGTH_SHORT).show();
}
}
final BroadcastReceiver broadcastReceiver = new BroadcastReceiver(){
@Override
public void onReceive(Context context, Intent intent) {
// TODO Auto-generated method stub
String action = intent.getAction();
//when discovery finds a device
if(BluetoothDevice.ACTION_FOUND.equals(action)){
//Get bluetooth device object from intent
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
// Add name and MAC address to adapter
madapter.add(device.getName()+"\n"+device.getAddress());
madapter.notifyDataSetChanged();
}
}
};
public void search(View v){
if(bluetoothAdapter.isDiscovering()){
bluetoothAdapter.cancelDiscovery();
}
else{
madapter.clear();
bluetoothAdapter.startDiscovery();
registerReceiver(broadcastReceiver, new IntentFilter(BluetoothDevice.ACTION_FOUND));
}
}
public void off(View v){
bluetoothAdapter.disable();
textStatus.setText("Disabled");
Toast.makeText(getApplicationContext(), "Bluetooth Disabled", Toast.LENGTH_SHORT).show();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
activity_main.xml中
<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=".MainActivity"
android:background="#112f33" >
<Button
android:id="@+id/buttonOn"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginLeft="44dp"
android:layout_marginTop="148dp"
android:text="@string/button_on"
android:textColor="#ffffff" />
<Button
android:id="@+id/buttonOff"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/buttonOn"
android:layout_alignBottom="@+id/buttonOn"
android:layout_alignParentRight="true"
android:layout_marginRight="36dp"
android:text="@string/button_off"
android:textColor="#ffffff"/>
<Button
android:id="@+id/buttonPaired"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/buttonOn"
android:layout_alignRight="@+id/buttonOff"
android:layout_below="@+id/buttonOn"
android:layout_marginTop="21dp"
android:text="@string/button_paired"
android:textColor="#ffffff" />
<Button
android:id="@+id/buttonSearch"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/buttonPaired"
android:layout_alignRight="@+id/buttonPaired"
android:layout_below="@+id/buttonPaired"
android:layout_marginTop="28dp"
android:text="@string/button_search"
android:textColor="#ffffff" />
<TextView
android:id="@+id/textStatus"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="@+id/buttonOff"
android:layout_alignLeft="@+id/buttonOn"
android:layout_marginBottom="60dp"
android:text="@string/text_status"
android:textColor="#ffffff"
android:textAppearance="?android:attr/textAppearanceMedium" />
<TextView
android:id="@+id/textUpdateStatus"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/textStatus"
android:layout_alignBottom="@+id/textStatus"
android:layout_alignLeft="@+id/buttonOff"
/>
<LinearLayout
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:orientation="vertical"
android:layout_below="@+id/buttonSearch">
<ListView
android:id="@+id/listView"
android:layout_height="wrap_content"
android:layout_width="wrap_content"></ListView>
</LinearLayout>
</RelativeLayout>
logcat的
04-10 13:15:22.704: E/AndroidRuntime(439): FATAL EXCEPTION: main
04-10 13:15:22.704: E/AndroidRuntime(439): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.bluetoothbasics/com.example.bluetoothbasics.MainActivity}: java.lang.NullPointerException
04-10 13:15:22.704: E/AndroidRuntime(439): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
04-10 13:15:22.704: E/AndroidRuntime(439): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
04-10 13:15:22.704: E/AndroidRuntime(439): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
04-10 13:15:22.704: E/AndroidRuntime(439): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
04-10 13:15:22.704: E/AndroidRuntime(439): at android.os.Handler.dispatchMessage(Handler.java:99)
04-10 13:15:22.704: E/AndroidRuntime(439): at android.os.Looper.loop(Looper.java:123)
04-10 13:15:22.704: E/AndroidRuntime(439): at android.app.ActivityThread.main(ActivityThread.java:3683)
04-10 13:15:22.704: E/AndroidRuntime(439): at java.lang.reflect.Method.invokeNative(Native Method)
04-10 13:15:22.704: E/AndroidRuntime(439): at java.lang.reflect.Method.invoke(Method.java:507)
04-10 13:15:22.704: E/AndroidRuntime(439): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-10 13:15:22.704: E/AndroidRuntime(439): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-10 13:15:22.704: E/AndroidRuntime(439): at dalvik.system.NativeStart.main(Native Method)
04-10 13:15:22.704: E/AndroidRuntime(439): Caused by: java.lang.NullPointerException
04-10 13:15:22.704: E/AndroidRuntime(439): at com.example.bluetoothbasics.MainActivity.onCreate(MainActivity.java:96)
04-10 13:15:22.704: E/AndroidRuntime(439): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-10 13:15:22.704: E/AndroidRuntime(439): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
04-10 13:15:22.704: E/AndroidRuntime(439): ... 11 more
请帮助查找错误。谢谢。
答案 0 :(得分：1)
您应该在使用之前通过findViewById初始化ListView listView;
onCreate() {
...
listView = (ListView) findViewById(R.id.listView);
...
}
答案 1 :(得分：0)
我无法确定因为行号丢失但我猜你在这行上有一个nullpointer因为listView为null：
listView.setAdapter（madapter）;
=＆GT;如果这是问题，请在设置适配器之前初始化listView。