我已经开始尝试学习如何在Android平台上编程，我制作了这个应该与蓝牙模块通信的程序。但是，每次启动它时，它立即崩溃，并且不幸的是，“程序名称”已停止工作。怎么了？
Main Activity
package com.example.enge1104;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Set;
import java.util.UUID;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity {
BluetoothAdapter mBluetoothAdapter;
BluetoothSocket mmSocket;
BluetoothDevice mmDevice;
OutputStream mmOutputStream;
InputStream mmInputStream;
TextView myLabel;
Button buttonLeft;
Button buttonRight;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttonLeft = (Button)findViewById(R.id.buttonLeft);
buttonRight = (Button)findViewById(R.id.buttonRight);
myLabel = (TextView)findViewById(R.id.display);
buttonLeft.setOnTouchListener(new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
switch(event.getAction()) {
case MotionEvent.ACTION_DOWN:
try {
sendData(0);
} catch (IOException e) {}
break;
case MotionEvent.ACTION_UP:
try {
sendData(1);
} catch (IOException e) {}
break;
}
return false;
}
});
buttonRight.setOnTouchListener(new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
switch(event.getAction()) {
case MotionEvent.ACTION_DOWN:
try {
sendData(2);
} catch (IOException e) {}
break;
case MotionEvent.ACTION_UP:
try {
sendData(3);
} catch (IOException e) {}
break;
}
return false;
}
});
try
{
findBT();
openBT();
}
catch (IOException ex) { }
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
void sendData( int newValue) throws IOException
{
mmOutputStream.write(newValue);
}
void findBT()
{
mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
if (!mBluetoothAdapter.isEnabled()) {
Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent,0);
}
mmDevice = null;
Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();
// If there are paired devices
if (pairedDevices.size() > 0) {
for (BluetoothDevice device : pairedDevices) {
if(device.getName().equals("HC-06")) //Name of bluetooth module
{
mmDevice = device;
break;
}
}
}
}
void openBT() throws IOException
{
UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805f9b34fb"); //Standard SerialPortService ID
mmSocket = null;
mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);
mmSocket.connect();
mmOutputStream = mmSocket.getOutputStream();
myLabel.setText("Bluetooth Opened");
}
@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;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
}}
XML文件
<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.enge1104.MainActivity$PlaceholderFragment" >
<Button
android:id="@+id/buttonLeft"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:layout_marginRight="46dp"
android:layout_toLeftOf="@+id/buttonRight"
android:text="@string/button_left" />
<Button
android:id="@+id/buttonRight"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/buttonLeft"
android:layout_alignBottom="@+id/buttonLeft"
android:layout_alignParentRight="true"
android:layout_marginRight="67dp"
android:text="@string/button_right" />
<TextView
android:id="@+id/display"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="46dp"
android:text="@string/disDisplay" />
</RelativeLayout>
的strings.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="app_name">ENGE1104</string>
<string name="hello_world">Hello world!</string>
<string name="action_settings">Settings</string>
<string name="button_right">Right</string>
<string name="button_left">Left</string>
<string name="disDisplay">Not Connected</string>
</resources>
清单
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.enge1104"
android:versionCode="1"
android:versionName="1.0" >
<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="19" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.enge1104.MainActivity"
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>
</manifest>
log-cat
04-21 15:36:14.572: I/Process(25563): Sending signal. PID: 25563 SIG: 9
04-21 15:36:26.512: D/AndroidRuntime(25760): Shutting down VM
04-21 15:36:26.512: W/dalvikvm(25760): threadid=1: thread exiting with uncaught exception (group=0x41522ba8)
04-21 15:36:26.512: E/AndroidRuntime(25760): FATAL EXCEPTION: main
04-21 15:36:26.512: E/AndroidRuntime(25760): Process: com.example.enge1104, PID: 25760
04-21 15:36:26.512: E/AndroidRuntime(25760): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.enge1104/com.example.enge1104.MainActivity}: java.lang.NullPointerException
04-21 15:36:26.512: E/AndroidRuntime(25760): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
04-21 15:36:26.512: E/AndroidRuntime(25760): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
04-21 15:36:26.512: E/AndroidRuntime(25760): at android.app.ActivityThread.access$800(ActivityThread.java:135)
04-21 15:36:26.512: E/AndroidRuntime(25760): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
04-21 15:36:26.512: E/AndroidRuntime(25760): at android.os.Handler.dispatchMessage(Handler.java:102)
04-21 15:36:26.512: E/AndroidRuntime(25760): at android.os.Looper.loop(Looper.java:136)
04-21 15:36:26.512: E/AndroidRuntime(25760): at android.app.ActivityThread.main(ActivityThread.java:5017)
04-21 15:36:26.512: E/AndroidRuntime(25760): at java.lang.reflect.Method.invokeNative(Native Method)
04-21 15:36:26.512: E/AndroidRuntime(25760): at java.lang.reflect.Method.invoke(Method.java:515)
04-21 15:36:26.512: E/AndroidRuntime(25760): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-21 15:36:26.512: E/AndroidRuntime(25760): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-21 15:36:26.512: E/AndroidRuntime(25760): at dalvik.system.NativeStart.main(Native Method)
04-21 15:36:26.512: E/AndroidRuntime(25760): Caused by: java.lang.NullPointerException
04-21 15:36:26.512: E/AndroidRuntime(25760): at com.example.enge1104.MainActivity.onCreate(MainActivity.java:51)
04-21 15:36:26.512: E/AndroidRuntime(25760): at android.app.Activity.performCreate(Activity.java:5231)
04-21 15:36:26.512: E/AndroidRuntime(25760): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-21 15:36:26.512: E/AndroidRuntime(25760): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
04-21 15:36:26.512: E/AndroidRuntime(25760): ... 11 more
04-21 15:36:29.032: I/Process(25760): Sending signal. PID: 25760 SIG: 9
答案 0 :(得分：0)
在意识到我做错了之后，那个setContentView（R.layout.activity_main）;正在查看activity_main.xml的所有内容，但我的布局实际上是在fragment_main.xml中。因此，我将fragment_main.xml中的内容移动到activity_main.xml。