Android关于无法启动活动componentinfo

Question

I'm a new programmer,recently i have a bug but can't solve

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.Bl
uetoothChat/com.example.android.BluetoothFileTran.FileTranActivity}:
java.lang.NullPointerException

logcat stack trace

04-26 10:19:43.613: E/BluetoothChat(21754): +++ ON CREATE +++
04-26 10:19:44.213: E/CheckPermission(21754): _bluetooth code = 1 
04-26 10:19:44.213: E/BluetoothChat(21754): ++ ON START ++
04-26 10:19:44.233: E/BluetoothChat(21754): + ON RESUME +
04-26 10:19:44.233: E/CheckPermission(21754): _bluetooth code = 13 
04-26 10:19:45.643: E/BluetoothChat(21754): - ON PAUSE -
04-26 10:19:47.223: E/BluetoothChat(21754): + ON RESUME +
04-26 10:19:55.093: E/BluetoothChat(21754): - ON PAUSE -
04-26 10:20:21.363: E/AndroidRuntime(21754): FATAL EXCEPTION: main
04-26 10:20:21.363: E/AndroidRuntime(21754): Process: com.example.android.BluetoothChat, PID: 21754
04-26 10:20:21.363: E/AndroidRuntime(21754): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.BluetoothChat/com.example.android.BluetoothFileTran.FileTranActivity}: java.lang.NullPointerException
04-26 10:20:21.363: E/AndroidRuntime(21754):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2190)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2250)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at android.app.ActivityThread.access$800(ActivityThread.java:139)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1200)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at android.os.Handler.dispatchMessage(Handler.java:102)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at android.os.Looper.loop(Looper.java:136)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at android.app.ActivityThread.main(ActivityThread.java:5049)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at java.lang.reflect.Method.invokeNative(Native Method)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at java.lang.reflect.Method.invoke(Method.java:515)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:818)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:634)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at dalvik.system.NativeStart.main(Native Method)
04-26 10:20:21.363: E/AndroidRuntime(21754): Caused by: java.lang.NullPointerException
04-26 10:20:21.363: E/AndroidRuntime(21754):    at com.example.android.BluetoothFileTran.FileTranActivity.onCreate(FileTranActivity.java:66)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at android.app.Activity.performCreate(Activity.java:5293)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at de.robv.android.xposed.XposedBridge.invokeOriginalMethodNative(Native Method)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at de.robv.android.xposed.XposedBridge.handleHookedMethod(XposedBridge.java:631)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at android.app.Activity.performCreate(Native Method)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-26 10:20:21.363: E/AndroidRuntime(21754):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2154)
04-26 10:20:21.363: E/AndroidRuntime(21754):    ... 12 more

here is Bluetoooth.java

package com.example.android.BluetoothChat;

import com.example.android.BluetoothChat.R;
import com.example.android.BluetoothChat.service.BluetoothChatService;
import com.example.android.BluetoothFileTran.FileTranActivity;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.ContentValues;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Message;
import android.util.Log;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.inputmethod.EditorInfo;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;


public class BluetoothChat extends Activity {

    public static final String SEND_FILE_NAME = "sendFileName";
    public static final int REQUEST_FILE = 1000;    
    private static String mSendFileName ;
    private Handler mOthHandler;   
    private static String mAddress ;

    private static final String TAG = "BluetoothChat";
    private static final boolean D = true;

    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;

    public static final String DEVICE_NAME = "device_name";
    public static final String TOAST = "toast";

    private static final int REQUEST_CONNECT_DEVICE = 1;
    private static final int REQUEST_ENABLE_BT = 2;

    private ListView mConversationView;
    private EditText mOutEditText;
    private Button mSendButton;

    private String mConnectedDeviceName = null;
    private ArrayAdapter<String> mConversationArrayAdapter;
    private StringBuffer mOutStringBuffer;
    private BluetoothAdapter mBluetoothAdapter = null;
    private BluetoothChatService mChatService = null;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if(D) Log.e(TAG, "+++ ON CREATE +++");
        setContentView(R.layout.main);

        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();


        if (mBluetoothAdapter == null) {
            Toast.makeText(this, "Bluetooth is not available", Toast.LENGTH_LONG).show();
            finish();
            return;
        }
    }

    @Override
    public void onStart() {
        super.onStart();
        if(D) Log.e(TAG, "++ ON START ++");

        if (!mBluetoothAdapter.isEnabled()) {
            Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableIntent, REQUEST_ENABLE_BT);
        } else {
            if (mChatService == null) setupChat();
        }
    }

    private void setupChat() {
        Log.d(TAG, "setupChat()");

        mConversationArrayAdapter = new ArrayAdapter<String>(this, R.layout.message);
        mConversationView = (ListView) findViewById(R.id.in);
        mConversationView.setAdapter(mConversationArrayAdapter);

        mOutEditText = (EditText) findViewById(R.id.edit_text_out);
        mOutEditText.setOnEditorActionListener(mWriteListener);

        mSendButton = (Button) findViewById(R.id.button_send);
        mSendButton.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                TextView view = (TextView) findViewById(R.id.edit_text_out);
                String message = view.getText().toString();
                sendMessage(message);
            }
        });

        mChatService = new BluetoothChatService(this, mHandler);

        mOutStringBuffer = new StringBuffer("");
    }    

    @Override
    public synchronized void onResume() {
        super.onResume();
        if(D) Log.e(TAG, "+ ON RESUME +");

        if (mChatService != null) {
            if (mChatService.getState() == BluetoothChatService.STATE_NONE) {
              mChatService.start();
            }
        }
    }

    private TextView.OnEditorActionListener mWriteListener =
        new TextView.OnEditorActionListener() {
        public boolean onEditorAction(TextView view, int actionId, KeyEvent event) {
            //EditorInfo.IME_NULL  KeyEvent.ACTION_UP
            if (actionId == EditorInfo.IME_NULL && event.getAction() == KeyEvent.ACTION_UP) {
                String message = view.getText().toString();
                sendMessage(message);
            }
            if(D) Log.i(TAG, "END onEditorAction");
            return true;
        }
    };


    @Override
    public synchronized void onPause() {
        super.onPause();
        if(D) Log.e(TAG, "- ON PAUSE -");
    }

    @Override
    public void onStop() {
        super.onStop();
        if(D) Log.e(TAG, "-- ON STOP --");
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        if (mChatService != null) mChatService.stop();
        if(D) Log.e(TAG, "--- ON DESTROY ---");
    }


    private void sendMessage(String message) {
        if (mChatService.getState() != BluetoothChatService.STATE_CONNECTED) {
            Toast.makeText(this, R.string.not_connected, Toast.LENGTH_SHORT).show();
            return;
        }

        if (message.length() > 0) {
            byte[] send = message.getBytes();
            mChatService.write(send);

            mOutStringBuffer.setLength(0);
            mOutEditText.setText(mOutStringBuffer);
        }
    }



    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 BluetoothChatService.STATE_CONNECTED:
                    mConversationArrayAdapter.clear();
                    break;
                case BluetoothChatService.STATE_CONNECTING:
                    break;
                case BluetoothChatService.STATE_LISTEN:
                case BluetoothChatService.STATE_NONE:
                    break;
                }
                break;
            case MESSAGE_WRITE:
                byte[] writeBuf = (byte[]) msg.obj;
                String writeMessage = new String(writeBuf);
                mConversationArrayAdapter.add("Me:  " + writeMessage);
                break;
            case MESSAGE_READ:
                byte[] readBuf = (byte[]) msg.obj;
                String readMessage = new String(readBuf, 0, msg.arg1);
                mConversationArrayAdapter.add(mConnectedDeviceName+":  " + readMessage);
                break;
            case MESSAGE_DEVICE_NAME:
                mConnectedDeviceName = msg.getData().getString(DEVICE_NAME);
//                mAddress = msg.getData().getString(DEVICE_ADDRESS);
                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;
            }
        }
    };

    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        if(D) Log.d(TAG, "onActivityResult " + resultCode);
        switch (requestCode) {
        case REQUEST_CONNECT_DEVICE:
            if (resultCode == Activity.RESULT_OK) {
                mAddress = data.getExtras()
                        .getString(DeviceListActivity.EXTRA_DEVICE_ADDRESS);
                BluetoothDevice device = mBluetoothAdapter.getRemoteDevice(mAddress);
                mChatService.connect(device);
            }
            break;
        case REQUEST_ENABLE_BT:
            if (resultCode == Activity.RESULT_OK) {
                setupChat();
            } else {
                Log.d(TAG, "BT not enabled");
                Toast.makeText(this, R.string.bt_not_enabled_leaving, Toast.LENGTH_SHORT).show();
                finish();
            }
            break;
        case REQUEST_FILE:
            if (resultCode == Activity.RESULT_OK) {
                mSendFileName = data.getExtras().getString(SEND_FILE_NAME);
                doSendFileByBluetooth();
            }
            break;
        }
    }

    private void doSendFileByBluetooth() {
        String filePath = mSendFileName.trim();
        if(!filePath.equals("null")){
            if(null == mOthHandler){
                HandlerThread handlerThread = new HandlerThread("other_thread");
                handlerThread.start();
                mOthHandler = new Handler(handlerThread.getLooper());
            }
            mOthHandler.post(new Runnable() {

                @Override
                public void run() {
                    ContentValues cv = new ContentValues();
                    String uri = "file://" + mSendFileName.trim();
                    cv.put("uri", uri);
                    cv.put("destination", mAddress.trim());
                    cv.put("direction", 0);
                    Long ts = System.currentTimeMillis();
                    cv.put("timestamp", ts);
                    getContentResolver().insert(Uri.parse("content://com.android.bluetooth.opp/btopp"), cv);
                }
            });
        }else {
            Toast.makeText(BluetoothChat.this, "请选择要发送的文件!", Toast.LENGTH_LONG).show();
        }
    }

    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);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.option_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case R.id.scan:
            Intent serverIntent = new Intent(this, DeviceListActivity.class);
            startActivityForResult(serverIntent, REQUEST_CONNECT_DEVICE);
            return true;
        case R.id.discoverable:
            ensureDiscoverable();
            return true;
        case R.id.file_transport:    
            Intent fileIntent = new Intent(this, FileTranActivity.class);
            startActivityForResult(fileIntent, REQUEST_FILE);
            return true;
        }
        return false;
    }

}

here is FileTranActivity.java

package com.example.android.BluetoothFileTran;

import java.io.File;

import com.example.android.BluetoothChat.BluetoothChat;
import com.example.android.BluetoothChat.R;
import com.example.android.BluetoothFileTran.adapter.AdapterManager;
import com.example.android.BluetoothFileTran.adapter.FileListAdapter;

import android.app.Activity;
import android.content.Intent;
import android.graphics.Color;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.HandlerThread;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;

public class FileTranActivity extends Activity {


    ListView mFileListView;
    FileListAdapter mFileListAdapter;
    AdapterManager mAdapterManager;

    private Handler mOtherHandler;
    private Runnable updateFileListRunnable;

    private File file;   

    private String sdcardPath;  
    private String path;    

    Button mBackBtn;  
    Button mEnsureBtn;   
    Button mCancelBtn;   

    TextView mLastClickView;  
    TextView mNowClickView;  
    private boolean isSelected = false;   

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.file_list);

        setResult(Activity.RESULT_CANCELED);

        mFileListView = (ListView) findViewById(R.id.fileListView);
        mBackBtn = (Button) findViewById(R.id.selectFileBackBtn);
        mEnsureBtn = (Button) findViewById(R.id.selectFileEnsureBtn);
        mCancelBtn = (Button) findViewById(R.id.selectFileCancelBtn);

        sdcardPath = Environment.getExternalStorageDirectory().getAbsolutePath();
        path = sdcardPath;

        mAdapterManager = BluetoothApplication.getInstance().getAdapterManager();
        mFileListView.setAdapter(mAdapterManager.getFileListAdapter());
        mAdapterManager.updateFileListAdapter(path);

        mFileListView.setOnItemClickListener(mFileListOnItemClickListener);
        mBackBtn.setOnClickListener(mBackBtnClickListener);
        mEnsureBtn.setOnClickListener(mEnsureBtnClickListener);
        mCancelBtn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                FileTranActivity.this.finish();
            }
        });

    }

    private OnItemClickListener mFileListOnItemClickListener = new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            file = (File) mFileListView.getAdapter().getItem(position);
            if(file.isFile()){ 
                if(null != mLastClickView){
                    mLastClickView.setTextColor(Color.WHITE);
                }
                mNowClickView = (TextView) view.findViewById(R.id.fileNameTV);
                mNowClickView.setTextColor(Color.BLUE);
                isSelected = true;
                mLastClickView = mNowClickView;
            }else {
                path = file.getAbsolutePath();
                updateFileList();
            }                           
        }

    };

    private OnClickListener mBackBtnClickListener = new OnClickListener() {

        @Override
        public void onClick(View v) {
            if(path.equals(sdcardPath)){
                return ;
            }
            path = path.substring(0, path.lastIndexOf("/"));
            updateFileList();
        }
    };


    private OnClickListener mEnsureBtnClickListener = new OnClickListener() {

        @Override
        public void onClick(View v) {
            if(!isSelected){
                Toast.makeText(FileTranActivity.this, "请选择文件!", Toast.LENGTH_LONG).show();
                return ;
            }
            Intent intent = new Intent();
            intent.putExtra(BluetoothChat.SEND_FILE_NAME, file.getAbsolutePath());
            setResult(Activity.RESULT_OK, intent);
            FileTranActivity.this.finish();
        }
    };

    private void updateFileList() {
        if(null != mLastClickView){
            mLastClickView.setTextColor(Color.WHITE);
            mLastClickView = null;
            isSelected = false;
        }
        if(null == updateFileListRunnable){
            updateFileListRunnable = new Runnable() {

                @Override
                public void run() {

                    mAdapterManager.updateFileListAdapter(path);
                }
            };
        }
        if(null == mOtherHandler){
            HandlerThread handlerThread = new HandlerThread("other_thread");
            handlerThread.start();
            mOtherHandler = new Handler(handlerThread.getLooper());
        }
        mOtherHandler.post(updateFileListRunnable);
    }

}

then ,I find it point out the error in the FileTranActivity.java

mAdapterManager = BluetoothApplication.getInstance().getAdapterManager();

so ,here is BluetoothApplication.java

package com.example.android.BluetoothFileTran;


import com.example.android.BluetoothFileTran.adapter.AdapterManager;
import com.example.android.BluetoothFileTran.adapter.util.TouchObject;

import android.app.Application;

public class BluetoothApplication extends Application {
    private static BluetoothApplication application;

    private AdapterManager mAdapterManager;

    private TouchObject mTouchObject;

    @Override
    public void onCreate() {
        super.onCreate();
        if(null == application){
            application = this;
        }
        mTouchObject = new TouchObject();
    }

    public static BluetoothApplication getInstance(){
        return application;
    }

    public AdapterManager getAdapterManager() {
        return mAdapterManager;
    }

    public void setAdapterManager(AdapterManager adapterManager) {
        this.mAdapterManager = adapterManager;
    }

    public TouchObject getTouchObject() {
        return mTouchObject;
    }

    public void setTouchObject(TouchObject touchObject) {
        this.mTouchObject = touchObject;
    }

}

and AdapterManager.java

package com.example.android.BluetoothFileTran.adapter;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

import android.bluetooth.BluetoothDevice;
import android.content.Context;
import android.os.Handler;

import com.example.android.BluetoothChat.R;
import com.example.android.BluetoothFileTran.adapter.FileListAdapter;


public class AdapterManager {
    private Context mContext;   
    private FileListAdapter mFileListAdapter;    
    private List<BluetoothDevice> mDeviceList;   
    private List<File> mFileList;    
    private Handler mainHandler;   

    public AdapterManager(Context context){
        this.mContext = context;
    }


    public FileListAdapter getFileListAdapter(){
        if(null == mFileListAdapter){
            mFileList = new ArrayList<File>();
            mFileListAdapter = new FileListAdapter(mContext, mFileList, R.layout.file_list_item);
        }

        return mFileListAdapter;
    }


    public void clearDevice(){
        if(null != mDeviceList){
            mDeviceList.clear();
        }
    }


    public void addDevice(BluetoothDevice bluetoothDevice){
        mDeviceList.add(bluetoothDevice);
    }


    public void changeDevice(int listId, BluetoothDevice bluetoothDevice){
        mDeviceList.remove(listId);
        mDeviceList.add(listId, bluetoothDevice);
    }


    public void updateFileListAdapter(String path){
        mFileList.clear();
        mFileList.addAll(getFileList(path));
        if(null == mainHandler){
            mainHandler = new Handler(mContext.getMainLooper());
        }
        mainHandler.post(new Runnable() {

            @Override
            public void run() {
                mFileListAdapter.notifyDataSetChanged();
            }
        });
    }


    public List<BluetoothDevice> getDeviceList() {
        return mDeviceList;
    }

    public static List<File> getFileList(String path){
        List<File> fileList = new ArrayList<File>();
        File[] files = new File(path).listFiles();
        if(files.length > 0){
            List<File> allFolder = new ArrayList<File>();
            List<File> allFile = new ArrayList<File>();
            for(File file : files){
                if(file.isFile()){
                    allFile.add(file);
                }else {
                    allFolder.add(file);
                }
            }
            fileList.addAll(allFolder);
            fileList.addAll(allFile);
        }

        return fileList;
    }
}

my xml is

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.example.android.BluetoothChat"
      android:versionCode="1"
      android:versionName="1.0" xmlns:tools="http://schemas.android.com/tools">
    <uses-sdk
        android:minSdkVersion="6"
        android:targetSdkVersion="18" tools:ignore="OldTargetApi"/>
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
    <uses-permission android:name="android.permission.BLUETOOTH" />
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    <application 
        android:allowBackup="true"
        android:label="@string/app_name"
        android:icon="@drawable/ic_launcher"
        android:theme="@style/AppTheme" >
        <activity android:name="com.example.android.BluetoothChat.BluetoothChat"
                  android:label="@string/app_name"
                  >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name="com.example.android.BluetoothChat.DeviceListActivity"
                  android:label="@string/select_device"
                  android:theme="@android:style/Theme.Dialog"
                  />
        <activity android:name="com.example.android.BluetoothFileTran.FileTranActivity"
                  android:label="@string/select_file"
                  android:theme="@android:style/Theme.Dialog"
                  />
    </application>
</manifest>

Answer 1

Register in the AndroidManifest the BluetoothFileTran class as application name in application tag:

<application 
    android:allowBackup="true"
    android:name="com.example.android.BluetoothFileTran"
    ...

Without this, the BluetoothFileTran will not be loaded, and onCreate will never invoked.

This will return a null reference in BluetoothApplication.getInstance() , which are causing your NullPointerException .

Reference

Notice: Your package in manifest, package="com.example.android.BluetoothChat" is different from the package that BluetoothFileTran is located (not in one of childs). I recommend you to use the package com.example.android instead of com.example.android.BluetoothChat in manifest tag.