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我无法理解这个问题。该行总是返回null，这会导致应用程序崩溃。该行是：为什么findFragmentById总是返回null
FragmentManager manager = activity.getFragmentManager();
DeviceListFragment fragment = (DeviceListFragment)
manager.findFragmentById(R.id.frag_list);
fragment.updateThisDevice((WifiP2pDevice) intent.getParcelableExtra(
WifiP2pManager.EXTRA_WIFI_P2P_DEVICE));
片段为空。更好地了解情况。我有这个两个活动
首先是P2P活动
package it.linup.maint.activity;
import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.wifi.p2p.WifiP2pConfig;
import android.net.wifi.p2p.WifiP2pDevice;
import android.net.wifi.p2p.WifiP2pManager;
import android.net.wifi.p2p.WifiP2pManager.*;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.Toast;
import com.github.hiteshsondhi88.sampleffmpeg.R;
public class P2P extends Activity implements ChannelListener,
DeviceListFragment.DeviceActionListener {
public static final String TAG = "wifidirectdemo";
private WifiP2pManager manager;
private boolean isWifiP2pEnabled = false;
private boolean retryChannel = false;
private final IntentFilter intentFilter = new IntentFilter();
private WifiP2pManager.Channel channel;
private BroadcastReceiver receiver = null;
/**
* @param isWifiP2pEnabled the isWifiP2pEnabled to set
*/
public void setIsWifiP2pEnabled(boolean isWifiP2pEnabled) {
this.isWifiP2pEnabled = isWifiP2pEnabled;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// add necessary intent values to be matched.
intentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);
intentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);
intentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);
intentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);
manager = (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE);
channel = manager.initialize(this, getMainLooper(), null);
}
/** register the BroadcastReceiver with the intent values to be matched */
@Override
public void onResume() {
super.onResume();
receiver = new WiFiDirectBroadcastReceiver(manager, channel, this);
registerReceiver(receiver, intentFilter);
}
@Override
public void onPause() {
super.onPause();
unregisterReceiver(receiver);
}
/**
* Remove all peers and clear all fields. This is called on
* BroadcastReceiver receiving a state change event.
*/
public void resetData() {
DeviceListFragment fragmentList = (DeviceListFragment) getFragmentManager()
.findFragmentById(R.id.frag_list);
DeviceDetailFragment fragmentDetails = (DeviceDetailFragment) getFragmentManager()
.findFragmentById(R.id.frag_detail);
if (fragmentList != null) {
fragmentList.clearPeers();
}
if (fragmentDetails != null) {
fragmentDetails.resetViews();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.action_items, menu);
return true;
}
/*
* (non-Javadoc)
* @see android.app.Activity#onOptionsItemSelected(android.view.MenuItem)
*/
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.atn_direct_enable:
if (manager != null && channel != null) {
// Since this is the system wireless settings activity, it's
// not going to send us a result. We will be notified by
// WiFiDeviceBroadcastReceiver instead.
startActivity(new Intent(android.provider.Settings.ACTION_WIRELESS_SETTINGS));
} else {
android.util.Log.e(TAG, "channel or manager is null");
}
return true;
case R.id.atn_direct_discover:
if (!isWifiP2pEnabled) {
Toast.makeText(P2P.this, R.string.p2p_off_warning,
Toast.LENGTH_SHORT).show();
return true;
}
final DeviceListFragment fragment = (DeviceListFragment) getFragmentManager()
.findFragmentById(R.id.frag_list);
fragment.onInitiateDiscovery();
manager.discoverPeers(channel, new WifiP2pManager.ActionListener() {
@Override
public void onSuccess() {
Toast.makeText(P2P.this, "Discovery Initiated",
Toast.LENGTH_SHORT).show();
}
@Override
public void onFailure(int reasonCode) {
Toast.makeText(P2P.this, "Discovery Failed : " + reasonCode,
Toast.LENGTH_SHORT).show();
}
});
return true;
default:
return super.onOptionsItemSelected(item);
}
}
@Override
public void showDetails(WifiP2pDevice device) {
DeviceDetailFragment fragment = (DeviceDetailFragment) getFragmentManager()
.findFragmentById(R.id.frag_detail);
fragment.showDetails(device);
}
@Override
public void connect(WifiP2pConfig config) {
manager.connect(channel, config, new WifiP2pManager.ActionListener() {
@Override
public void onSuccess() {
// WiFiDirectBroadcastReceiver will notify us. Ignore for now.
}
@Override
public void onFailure(int reason) {
Toast.makeText(P2P.this, "Connect failed. Retry.",
Toast.LENGTH_SHORT).show();
}
});
}
@Override
public void disconnect() {
final DeviceDetailFragment fragment = (DeviceDetailFragment) getFragmentManager()
.findFragmentById(R.id.frag_detail);
fragment.resetViews();
manager.removeGroup(channel, new WifiP2pManager.ActionListener() {
@Override
public void onFailure(int reasonCode) {
android.util.Log.d(TAG, "Disconnect failed. Reason :" + reasonCode);
}
@Override
public void onSuccess() {
fragment.getView().setVisibility(View.GONE);
}
});
}
@Override
public void onChannelDisconnected() {
// we will try once more
if (manager != null && !retryChannel) {
Toast.makeText(this, "Channel lost. Trying again", Toast.LENGTH_LONG).show();
resetData();
retryChannel = true;
manager.initialize(this, getMainLooper(), this);
} else {
Toast.makeText(this,
"Severe! Channel is probably lost premanently. Try Disable/Re-Enable P2P.",
Toast.LENGTH_LONG).show();
}
}
@Override
public void cancelDisconnect() {
/*
* A cancel abort request by user. Disconnect i.e. removeGroup if
* already connected. Else, request WifiP2pManager to abort the ongoing
* request
*/
if (manager != null) {
final DeviceListFragment fragment = (DeviceListFragment) getFragmentManager()
.findFragmentById(R.id.frag_list);
if (fragment.getDevice() == null
|| fragment.getDevice().status == WifiP2pDevice.CONNECTED) {
disconnect();
} else if (fragment.getDevice().status == WifiP2pDevice.AVAILABLE
|| fragment.getDevice().status == WifiP2pDevice.INVITED) {
manager.cancelConnect(channel, new WifiP2pManager.ActionListener() {
@Override
public void onSuccess() {
Toast.makeText(P2P.this, "Aborting connection",
Toast.LENGTH_SHORT).show();
}
@Override
public void onFailure(int reasonCode) {
Toast.makeText(P2P.this,
"Connect abort request failed. Reason Code: " + reasonCode,
Toast.LENGTH_SHORT).show();
}
});
}
}
}
}
第二activy是广播接收器，这是错误的是
WiFiDirectBroadcastReceiver
package it.linup.maint.activity;
import android.app.FragmentManager;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.net.NetworkInfo;
import android.net.wifi.p2p.WifiP2pDevice;
import android.net.wifi.p2p.WifiP2pManager;
import com.github.hiteshsondhi88.sampleffmpeg.R;
public class WiFiDirectBroadcastReceiver extends BroadcastReceiver {
private WifiP2pManager manager;
private WifiP2pManager.Channel channel;
private P2P activity;
/**
* @param manager WifiP2pManager system service
* @param channel Wifi p2p channel
* @param activity activity associated with the receiver
*/
public WiFiDirectBroadcastReceiver(WifiP2pManager manager, WifiP2pManager.Channel channel,
P2P activity) {
super();
this.manager = manager;
this.channel = channel;
this.activity = activity;
}
/*
* (non-Javadoc)
* @see android.content.BroadcastReceiver#onReceive(android.content.Context,
* android.content.Intent)
*/
@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)) {
// UI update to indicate wifi p2p status.
int state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1);
if (state == WifiP2pManager.WIFI_P2P_STATE_ENABLED) {
// Wifi Direct mode is enabled
activity.setIsWifiP2pEnabled(true);
} else {
activity.setIsWifiP2pEnabled(false);
activity.resetData();
}
android.util.Log.d(P2P.TAG, "P2P state changed - " + state);
} else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) {
// request available peers from the wifi p2p manager. This is an
// asynchronous call and the calling activity is notified with a
// callback on PeerListListener.onPeersAvailable()
if (manager != null) {
manager.requestPeers(channel, (WifiP2pManager.PeerListListener) activity.getFragmentManager()
.findFragmentById(R.id.frag_list));
}
android.util.Log.d(P2P.TAG, "P2P peers changed");
} else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) {
if (manager == null) {
return;
}
NetworkInfo networkInfo = (NetworkInfo) intent
.getParcelableExtra(WifiP2pManager.EXTRA_NETWORK_INFO);
if (networkInfo.isConnected()) {
// we are connected with the other device, request connection
// info to find group owner IP
DeviceDetailFragment fragment = (DeviceDetailFragment) activity
.getFragmentManager().findFragmentById(R.id.frag_detail);
manager.requestConnectionInfo(channel, fragment);
} else {
// It's a disconnect
activity.resetData();
}
} else if (WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION.equals(action)) {
FragmentManager manager = activity.getFragmentManager();
DeviceListFragment fragment = (DeviceListFragment) manager.findFragmentById(R.id.frag_list);
fragment.updateThisDevice((WifiP2pDevice) intent.getParcelableExtra(
WifiP2pManager.EXTRA_WIFI_P2P_DEVICE));
}
}
}
的P2P活动被称为在tabhost活动内部
Main活动
package it.linup.maint.activity;
import android.app.TabActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.TabHost;
import com.github.hiteshsondhi88.libffmpeg.FFmpeg;
import com.github.hiteshsondhi88.sampleffmpeg.R;
public class Main extends TabActivity
{
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// create the TabHost that will contain the Tabs
TabHost tabHost = (TabHost)findViewById(android.R.id.tabhost);
TabHost.TabSpec tab1 = tabHost.newTabSpec("Home");
TabHost.TabSpec tab2 = tabHost.newTabSpec("Log");
//TabHost.TabSpec tab3 = tabHost.newTabSpec("Debug");
TabHost.TabSpec tab4 = tabHost.newTabSpec("P2P");
// Set the Tab name and Activity
// that will be opened when particular Tab will be selected
tab1.setIndicator("Home");
tab1.setContent(new Intent(this, Home.class));
tab2.setIndicator("Log");
tab2.setContent(new Intent(this, Log.class));
//tab3.setIndicator("Debug");
//tab3.setContent(new Intent(this, DebugActivity.class));
tab4.setIndicator("P2P");
tab4.setContent(new Intent(this, P2P.class));
/** Add the tabs to the TabHost to display. */
tabHost.addTab(tab1);
tabHost.addTab(tab2);
tabHost.addTab(tab4);
//tabHost.addTab(tab3);
tabHost.setCurrentTab(1);
// tabHost.setCurrentTab(2);
tabHost.setCurrentTab(3);
tabHost.setCurrentTab(0);
}
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.options_menu, menu);
return true;
}
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.settings:
startActivity(new Intent(this, Settings.class));
return true;
case R.id.help:
startActivity(new Intent(this, Help.class));
return true;
default:
return super.onOptionsItemSelected(item);
}
}
public void setText(String text)
{
Log activity = (Log) getLocalActivityManager().getActivity("Log");
activity.refreshContent(text);
}
public FFmpeg getFfmpeg()
{
Home home = (Home) getLocalActivityManager().getActivity("Home");
return home.getFfmpeg();
}
}
日志错误是：
FATAL EXCEPTION: main
Process: com.github.hiteshsondhi88.sampleffmpeg, PID: 25845
java.lang.RuntimeException: Error receiving broadcast Intent { act=android.net.wifi.p2p.THIS_DEVICE_CHANGED flg=0x4000010 (has extras) } in [email protected]
at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:979)
at android.os.Handler.handleCallback(Handler.java:743)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:150)
at android.app.ActivityThread.main(ActivityThread.java:5665)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:822)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:712)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void it.linup.maint.activity.DeviceListFragment.updateThisDevice(android.net.wifi.p2p.WifiP2pDevice)' on a null object reference
at it.linup.maint.activity.WiFiDirectBroadcastReceiver.onReceive(WiFiDirectBroadcastReceiver.java:94)
at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:969)
at android.os.Handler.handleCallback(Handler.java:743)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:150)
at android.app.ActivityThread.main(ActivityThread.java:5665)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:822)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:712)
我不明白为什么我得到这个错误。
'第二个activity是一个BroadcastReceiver''Activity'绝对不是'BroadcastReceiver'。我也看不到你用你的ID添加一个片段。这就是你没有通过id找到它的原因 - 你不告诉系统它有这个ID。 –