我正在开发基于蓝牙的项目。我正在使用标签包含不同的页面。虽然包括按钮onclick监听器，但应用程序崩溃了。我提到了sdk的蓝牙聊天。在Setupchat（）中，我试图识别按钮并分配onclicklisteners。但该应用程序在onclicklistner上崩溃了。我检查了logcat它显示空指针异常。这是logcat输出。
08-11 16:25:08.003: E/AndroidRuntime(16481): FATAL EXCEPTION: main
08-11 16:25:08.003: E/AndroidRuntime(16481): Process: com.dispenser, PID: 16481
08-11 16:25:08.003: E/AndroidRuntime(16481): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dispenser/com.dispenser.MainActivity}: java.lang.NullPointerException
08-11 16:25:08.003: E/AndroidRuntime(16481): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2198)
08-11 16:25:08.003: E/AndroidRuntime(16481): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2257)
08-11 16:25:08.003: E/AndroidRuntime(16481): at android.app.ActivityThread.access$800(ActivityThread.java:139)
08-11 16:25:08.003: E/AndroidRuntime(16481): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
08-11 16:25:08.003: E/AndroidRuntime(16481): at android.os.Handler.dispatchMessage(Handler.java:102)
08-11 16:25:08.003: E/AndroidRuntime(16481): at android.os.Looper.loop(Looper.java:136)
08-11 16:25:08.003: E/AndroidRuntime(16481): at android.app.ActivityThread.main(ActivityThread.java:5086)
08-11 16:25:08.003: E/AndroidRuntime(16481): at java.lang.reflect.Method.invokeNative(Native Method)
08-11 16:25:08.003: E/AndroidRuntime(16481): at java.lang.reflect.Method.invoke(Method.java:515)
08-11 16:25:08.003: E/AndroidRuntime(16481): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
08-11 16:25:08.003: E/AndroidRuntime(16481): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
08-11 16:25:08.003: E/AndroidRuntime(16481): at dalvik.system.NativeStart.main(Native Method)
08-11 16:25:08.003: E/AndroidRuntime(16481): Caused by: java.lang.NullPointerException
08-11 16:25:08.003: E/AndroidRuntime(16481): at com.dispenser.MainActivity.setupChat(MainActivity.java:223)
08-11 16:25:08.003: E/AndroidRuntime(16481): at com.dispenser.MainActivity.onStart(MainActivity.java:195)
08-11 16:25:08.003: E/AndroidRuntime(16481): at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1194)
08-11 16:25:08.003: E/AndroidRuntime(16481): at android.app.Activity.performStart(Activity.java:5258)
08-11 16:25:08.003: E/AndroidRuntime(16481): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2171)
08-11 16:25:08.003: E/AndroidRuntime(16481): ... 11 more
我知道这个 nullpointerexception 何时到来。 如果我使用按钮而没有标识按钮，则nullpointerexception会引发。但我真的不知道这是什么。请帮帮我。
这是第195行和223
package com.dispenser;
import android.annotation.SuppressLint;
import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.Activity;
import android.app.FragmentTransaction;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.dispenser.adapter.TabsPagerAdapter;
public class MainActivity extends FragmentActivity implements ActionBar.TabListener, OnClickListener {
private ViewPager viewPager;
private TabsPagerAdapter mTabAdapter;
private ActionBar actionBar;
// Tab titles
private String[] tabs = { "Diagnostic", "Set" ,"Settings"};
// Debugging
private static final String TAG = "Main";
private static final boolean D = true;
// Message types sent from the BluetoothChatService Handler
public static final int MESSAGE_STATE_CHANGE = 1;
public static final int MESSAGE_READ = 2;
public static final int MESSAGE_WRITE = 3;
public static final int MESSAGE_DEVICE_NAME = 4;
public static final int MESSAGE_TOAST = 5;
// Key names received from the BluetoothChatService Handler
public static final String DEVICE_NAME = "device_name";
public static final String TOAST = "toast";
// Intent request codes
private static final int REQUEST_CONNECT_DEVICE = 1;
private static final int REQUEST_ENABLE_BT = 2;
// Layout Views
//private TextView mTitle;
private EditText mPS1,mPS2,mPS3,mFT,mFW,valve1,valve2,sPS1,sPS2,sPS3;
private Button mSendButtonOn,mEnable,mDisable,mSet;
private Button mSendButtonOff;
// Name of the connected device
private String mConnectedDeviceName;
// String buffer for outgoing messages
private StringBuffer mOutStringBuffer;
// Local Bluetooth adapter
private BluetoothAdapter mBluetoothAdapter;
// Member object for the chat services
private ChatService mChatService;
@SuppressLint("NewApi")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (D) {
Log.e(TAG, "+++ ON CREATE +++");
}
// Set up the window layout
//requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);
setContentView(R.layout.activity_main);
// getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE,
// R.layout.custom_title);
// Set up the custom title
// mTitle = (TextView) findViewById(R.id.title_left_text);
// mTitle.setText(R.string.app_name);
// mTitle = (TextView) findViewById(R.id.title_right_text);
// Get local Bluetooth adapter
mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
// If the adapter is null, then Bluetooth is not supported
if (mBluetoothAdapter == null) {
Toast.makeText(this, "Bluetooth is not available",
Toast.LENGTH_LONG).show();
finish();
return;
}
// Initialization
viewPager = (ViewPager) findViewById(R.id.pager);
actionBar = getActionBar();
mTabAdapter = new TabsPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(mTabAdapter);
actionBar.setHomeButtonEnabled(false);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Adding Tabs
for (String tab_name : tabs) {
actionBar.addTab(actionBar.newTab().setText(tab_name)
.setTabListener(this));
}
/**
* on swiping the viewpager make respective tab selected
* */
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
// on changing the page
// make respected tab selected
actionBar.setSelectedNavigationItem(position);
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
@Override
public void onPageScrollStateChanged(int arg0) {
}
});
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
// on tab selected
// show respected fragment view
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.scan:
// Launch the DeviceListActivity to see devices and do scan
Intent serverIntent = new Intent(this, DeviceListActivity.class);
startActivityForResult(serverIntent, REQUEST_CONNECT_DEVICE);
return true;
case R.id.discoverable:
// Ensure this device is discoverable by others
ensureDiscoverable();
return true;
}
return false;
}
@Override
public void onStart() {
super.onStart();
if (D) {
Log.e(TAG, "++ ON START ++");
}
// If BT is not on, request that it be enabled.
// setupChat() will then be called during onActivityResult
if (!mBluetoothAdapter.isEnabled()) {
Intent enableIntent = new Intent(
BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableIntent, REQUEST_ENABLE_BT);
// Otherwise, setup the chat session
} else {
if (mChatService == null) {
setupChat();
}
}
}
private void setupChat() {
mSet=(Button) findViewById(R.id.setBtn);
Log.d(TAG, "setupChat()");
// Diagnostic
mPS1=(EditText) findViewById(R.id.ps1);
mPS2=(EditText) findViewById(R.id.ps2);
mPS3=(EditText) findViewById(R.id.ps3);
mFT=(EditText) findViewById(R.id.ft);
mFW=(EditText) findViewById(R.id.fw);
valve1=(EditText) findViewById(R.id.valve1);
valve2=(EditText) findViewById(R.id.valve2);
//Set
sPS1=(EditText) findViewById(R.id.pressure1);
sPS2=(EditText) findViewById(R.id.pressure2);
sPS3=(EditText) findViewById(R.id.pressure3);
// mSet.setOnClickListener(MainActivity.this);
// Preference
// mSendButtonOff.setOnClickListener(MainActivity.this);
// Initialize the BluetoothChatService to perform bluetooth connections
mChatService = new ChatService(this, mHandler);
// Initialize the buffer for outgoing messages
mOutStringBuffer = new StringBuffer("");
}
@Override
public synchronized void onResume() {
super.onResume();
if (D) {
Log.e(TAG, "+ ON RESUME +");
}
// Performing this check in onResume() covers the case in which BT was
// not enabled during onStart(), so we were paused to enable it...
// onResume() will be called when ACTION_REQUEST_ENABLE activity
// returns.
if (mChatService != null) {
// Only if the state is STATE_NONE, do we know that we haven't
// started already
if (mChatService.getState() == ChatService.STATE_NONE) {
// Start the Bluetooth chat services
mChatService.start();
}
}
}
@Override
public synchronized void onPause() {
super.onPause();
if (D) {
Log.e(TAG, "- ON PAUSE -");
}
}
@Override
public void onDestroy() {
super.onDestroy();
// Stop the Bluetooth chat services
if (mChatService != null) {
mChatService.stop();
}
if (D) {
Log.e(TAG, "--- ON DESTROY ---");
}
}
private void ensureDiscoverable() {
if (D) {
Log.d(TAG, "ensure discoverable");
}
if (mBluetoothAdapter.getScanMode() != BluetoothAdapter.SCAN_MODE_CONNECTABLE_DISCOVERABLE) {
Intent discoverableIntent = new Intent(
BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
discoverableIntent.putExtra(
BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300);
startActivity(discoverableIntent);
}
}
/**
* Sends a message.
*
* @param message
* A string of text to send.
*/
private void sendMessage(String message) {
// Check that we're actually connected before trying anything
if (mChatService.getState() != ChatService.STATE_CONNECTED) {
Toast.makeText(this, R.string.not_connected, Toast.LENGTH_SHORT)
.show();
return;
}
// Check that there's actually something to send
if (message.length() > 0) {
// XXX !!!
message = message + "\r\n"; // terminate for pc bluetooth spp server
// Get the message bytes and tell the BluetoothChatService to write
byte[] send = message.getBytes();
mChatService.write(send);
// Reset out string buffer to zero and clear the edit text field
mOutStringBuffer.setLength(0);
// mOutEditText.setText(mOutStringBuffer);
}
}
// The Handler that gets information back from the BluetoothChatService
private final Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MESSAGE_STATE_CHANGE:
if (D) {
Log.i(TAG, "MESSAGE_STATE_CHANGE: " + msg.arg1);
}
switch (msg.arg1) {
case ChatService.STATE_CONNECTED:
Toast.makeText(getBaseContext(), R.string.title_connected_to+" " +mConnectedDeviceName, Toast.LENGTH_LONG).show();
// mTitle.append();
// mConversationArrayAdapter.clear();
break;
case ChatService.STATE_CONNECTING:
Toast.makeText(getBaseContext(), R.string.title_connecting, Toast.LENGTH_LONG).show();
break;
case ChatService.STATE_LISTEN:
case ChatService.STATE_NONE:
Toast.makeText(getBaseContext(), R.string.title_not_connected, Toast.LENGTH_LONG).show();
//mTitle.setText();
break;
}
break;
case MESSAGE_WRITE:
byte[] writeBuf = (byte[]) msg.obj;
// construct a string from the buffer
String writeMessage = new String(writeBuf);
// mConversationArrayAdapter.add("Me: " + writeMessage);
break;
case MESSAGE_READ:
byte[] readBuf = (byte[]) msg.obj;
// construct a string from the valid bytes in the buffer
final String readMessage = new String(readBuf, 0, 50);
// mConversationArrayAdapter.add(mConnectedDeviceName + ": "
// + readMessage);
Runnable done = new Runnable()
{
public void run()
{
String[] b=readMessage.split(",");
for(int i=0;i<b.length;i++){
// Toast.makeText(getBaseContext(), b[i], Toast.LENGTH_SHORT).show();
if(b[i].contains("PS1")){
String[] c=b[i].split("=");
if(c.length==2){
mPS1.setText(c[1]);
}
}
else if(b[i].contains("PS2")){
String[] c=b[i].split("=");
if(c.length==2){
mPS2.setText(c[1]);
}
}
else if(b[i].contains("PS3")){
String[] c=b[i].split("=");
if(c.length==2){
mPS3.setText(c[1]);
}
}
else if(b[i].contains("LPM")){
String[] c=b[i].split("=");
if(c.length==2){
mFW.setText(c[1]);
}
}
else{
}
// mPS1.append(b[i]);
}
}
};
done.run();
break;
case MESSAGE_DEVICE_NAME:
// save the connected device's name
mConnectedDeviceName = msg.getData().getString(DEVICE_NAME);
Toast.makeText(getApplicationContext(),
"Connected to " + mConnectedDeviceName,
Toast.LENGTH_SHORT).show();
break;
case MESSAGE_TOAST:
Toast.makeText(getApplicationContext(),
msg.getData().getString(TOAST), Toast.LENGTH_SHORT)
.show();
break;
}
}
};
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
if (D) {
Log.d(TAG, "onActivityResult " + resultCode);
}
switch (requestCode) {
case REQUEST_CONNECT_DEVICE:
// When DeviceListActivity returns with a device to connect
if (resultCode == Activity.RESULT_OK) {
// Get the device MAC address
String address = data.getExtras().getString(
DeviceListActivity.EXTRA_DEVICE_ADDRESS);
// Get the BLuetoothDevice object
BluetoothDevice device = mBluetoothAdapter
.getRemoteDevice(address);
// Attempt to connect to the device
mChatService.connect(device);
}
break;
case REQUEST_ENABLE_BT:
// When the request to enable Bluetooth returns
if (resultCode == Activity.RESULT_OK) {
// Bluetooth is now enabled, so set up a chat session
setupChat();
} else {
// User did not enable Bluetooth or an error occured
Log.d(TAG, "BT not enabled");
Toast.makeText(this, R.string.bt_not_enabled_leaving,
Toast.LENGTH_SHORT).show();
finish();
}
}
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
switch (v.getId()) {
case R.id.setBtn:
if(sPS1.getText().length()!=0){
float pressure1=Float.parseFloat(sPS1.getText().toString());
if(pressure1>0.0F && pressure1<20.0F)
sendMessage("PS1="+pressure1);
}
else{
sPS1.setError("Enter PS1");
}
if(sPS2.getText().length()!=0){
float pressure2=Float.parseFloat(sPS2.getText().toString());
if(pressure2>0.0F && pressure2<20.0F)
sendMessage("PS2="+pressure2);
}
else{
sPS2.setError("Enter PS2");
}
if(sPS3.getText().length()!=0){
float pressure3=Float.parseFloat(sPS3.getText().toString());
if(pressure3>0.0F && pressure3<20.0F)
sendMessage("PS3="+pressure3);
}
else{
sPS3.setError("Enter PS3");
}
break;
default:
break;
}
}
}
答案 0 :(得分：0)
您尚未实例化按钮
要使用 onClickListener（）按钮，您应该在 java 文件
中<\ n> 实例问题：如果我使用按钮而不识别按钮
您需要执行以下操作：
Button button = (Button) findViewById(R.id.button_identity);
底线：您应该拥有XML或java代码的身份。
希望它有效。
答案 1 :(得分：0)
我犯的错误是我试图在Mainactivity中包含onclicklistener而不是包括每个标签活动。我从MainActivity中删除了onclick侦听器，并在相应的活动选项卡中标识了按钮并包含onclicklistner。那解决了我的问题。