每当我在我的应用程序中点击Twitter的登录按钮时，它会将我带到webview，在那里它要求获得应用程序的授权，但是当我尝试共享文本时，它会显示以下给出的错误... ..ie（空指针异常）..我已经给出了下面的logcat以及我找到错误的代码。
logcat的
08-30 06:55:10.539: E/AndroidRuntime(1308): at com.Background_fb_twitter.share_text$2.onClick(share_text.java:55)
08-30 07:05:01.330: E/AndroidRuntime(1680): FATAL EXCEPTION: main
08-30 07:05:01.330: E/AndroidRuntime(1680): java.lang.NullPointerException
08-30 07:05:01.330: E/AndroidRuntime(1680): at com.Background_fb_twitter.share_text.postToWall(share_text.java:75)
08-30 07:05:01.330: E/AndroidRuntime(1680): at com.Background_fb_twitter.share_text$2.onClick(share_text.java:55)
08-30 07:05:01.330: E/AndroidRuntime(1680): at android.view.View.performClick(View.java:4204)
08-30 07:05:01.330: E/AndroidRuntime(1680): at android.view.View$PerformClick.run(View.java:17355)
08-30 07:05:01.330: E/AndroidRuntime(1680): at android.os.Handler.handleCallback(Handler.java:725)
08-30 07:05:01.330: E/AndroidRuntime(1680): at android.os.Handler.dispatchMessage(Handler.java:92)
08-30 07:05:01.330: E/AndroidRuntime(1680): at android.os.Looper.loop(Looper.java:137)
08-30 07:05:01.330: E/AndroidRuntime(1680): at android.app.ActivityThread.main(ActivityThread.java:5041)
08-30 07:05:01.330: E/AndroidRuntime(1680): at java.lang.reflect.Method.invokeNative(Native Method)
08-30 07:05:01.330: E/AndroidRuntime(1680): at java.lang.reflect.Method.invoke(Method.java:511)
08-30 07:05:01.330: E/AndroidRuntime(1680): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
08-30 07:05:01.330: E/AndroidRuntime(1680): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
08-30 07:05:01.330: E/AndroidRuntime(1680): at dalvik.system.NativeStart.main(Native Method)
Background_fb_Activity
package com.Background_fb_twitter;
import com.facebook.android.DialogError;
import com.facebook.android.Facebook;
import com.facebook.android.FacebookError;
import com.facebook.android.Facebook.DialogListener;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;
public class Background_fb_twitterActivity extends Activity {
private Button btn_fb;
private Button btn_tw;
private Button btn_share;
/** face book details */
static final String APP_ID = "XXXXXXXXXX";
static final String[] PERMISSIONS = new String[] { "publish_stream" };
static final String TOKEN = "1685102257-7K2lwqoBlgi1xifnZGOoWbZPLAHHVyNFlLwW6iZ";
static final String EXPIRES = "expires_in";
static final String KEY = "facebook-credentials";
static Facebook facebook1;
private boolean FB_LOGIN = false;
/** ---------------------------------- */
private boolean TWEET = false;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
btn_fb = (Button) findViewById(R.id.btn_fb);
btn_tw = (Button) findViewById(R.id.btn_twitter);
btn_share = (Button) findViewById(R.id.btn_share);
btn_fb.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
facebook1 = new Facebook(APP_ID);
loginAndPostToWall();
}
});
btn_tw.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent i = new Intent(getApplicationContext(),
PrepareRequestTokenActivity.class);
i.putExtra("tweet_msg", "");
startActivity(i);
TWEET = true;
}
});
btn_share.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
startActivity(new Intent(Background_fb_twitterActivity.this, share_text.class));
/*if (FB_LOGIN && TWEET) {
//show_alert();
}
else
{
Toast.makeText(Background_fb_twitterActivity.this,
"Pleaes Login To facebook & Twitter!", Toast.LENGTH_SHORT)
.show();
}*/
}
});
}
/** facebook methods---------------------------------------------start */
public void loginAndPostToWall() {
facebook1.authorize(this, PERMISSIONS, Facebook.FORCE_DIALOG_AUTH,
new LoginDialogListener());
}
class LoginDialogListener implements DialogListener {
public void onComplete(Bundle values) {
saveCredentials(facebook1);
FB_LOGIN = true;
}
public void onFacebookError(FacebookError error) {
showToast("Authentication with Facebook failed!");
}
public void onError(DialogError error) {
showToast("Authentication with Facebook failed!");
}
public void onCancel() {
showToast("Authentication with Facebook cancelled!");
}
}
private void showToast(String message) {
Toast.makeText(getApplicationContext(), message, Toast.LENGTH_SHORT)
.show();
}
public boolean saveCredentials(Facebook facebook) {
Editor editor = getApplicationContext().getSharedPreferences(KEY,
Context.MODE_PRIVATE).edit();
editor.putString(TOKEN, facebook.getAccessToken());
editor.putLong(EXPIRES, facebook.getAccessExpires());
return editor.commit();
}
public boolean restoreCredentials(Facebook facebook) {
SharedPreferences sharedPreferences = getApplicationContext()
.getSharedPreferences(KEY, Context.MODE_PRIVATE);
facebook.setAccessToken(sharedPreferences.getString(TOKEN, null));
facebook.setAccessExpires(sharedPreferences.getLong(EXPIRES, 0));
return facebook.isSessionValid();
}
/** facebook methods---------------------------------------------end */
}
Share_text.java ..（此文件中的错误Iam得到）。
package com.Background_fb_twitter;
import com.facebook.android.Facebook;
import android.app.Activity;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Bundle;
import android.os.Handler;
import android.preference.PreferenceManager;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class share_text extends Activity {
private EditText edit;
private Button btns;
/** face book details */
static final String APP_ID = "XXXXXXXXXX";
static final String[] PERMISSIONS = new String[] { "publish_stream" };
static final String TOKEN = "access_token";
static final String EXPIRES = "expires_in";
static final String KEY = "facebook-credentials";
static Facebook facebook1;
private boolean FB_LOGIN = false;
/** ---------------------------------- */
private SharedPreferences prefs1;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.share_alert);
this.prefs1 = PreferenceManager.getDefaultSharedPreferences(this);
edit = (EditText) findViewById(R.id.editText1);
btns = (Button) findViewById(R.id.button1);
btns.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
String str = edit.getText().toString();
if (str != "") {
postToWall(str, share_text.this);
if (TwitterUtils.isAuthenticated(prefs1)) {
sendTweet(share_text.this, str);
}
} else {
edit.setError("Please Enter Text!");
}
}
});
}
public static void postToWall(String message, Context con) {
facebook1 = new Facebook(APP_ID);
String st = get_token__(con);
Bundle parameters = new Bundle();
parameters.putString("message", message);
parameters.putString("description", "topic share");
if (st.length() > 0) {
parameters.putString("access_token", "" + st);
}
try {
facebook1.request("me");
String response = facebook1.request("me/feed", parameters, "POST");
Log.d("Tests--->*************", "got response: " + response);
if (response == null
|| response.equals("")
|| response.equals("false")
|| response
.equalsIgnoreCase("{\"error\":{\"message\":\"An active access token must be used to query information about the current user.\",\"type\":\"OAuthException\",\"code\":2500}}")) {
showToast("Blank response. please loginf again in facebook",
con);
clear_fb_data(con);
} else {
showToast("Message posted to your facebook wall!", con);
}
} catch (Exception e) {
showToast("Failed to post to wall!", con);
e.printStackTrace();
}
}
private static String get_token__(Context con) {
// TODO Auto-generated method stub
SharedPreferences sharedPreferences = con.getSharedPreferences(KEY,
Context.MODE_PRIVATE);
return sharedPreferences.getString(TOKEN, null);
}
private static void clear_fb_data(Context con) {
// TODO Auto-generated method stub
SharedPreferences se = PreferenceManager
.getDefaultSharedPreferences(con);
Editor editor = se.edit();
editor.remove(TOKEN);
editor.remove(EXPIRES);
editor.commit();
}
private static void showToast(String message, Context con) {
Toast.makeText(con, message, Toast.LENGTH_SHORT).show();
}
/** twitter methods-------------------------- start */
private final static Handler mTwitterHandler = new Handler();
private static SharedPreferences prefs;
public static boolean TWEET_LOGIN = false;
final static Runnable mUpdateTwitterNotification = new Runnable() {
public void run() {
}
};
public static void sendTweet(Context con, final String msj) {
prefs = PreferenceManager.getDefaultSharedPreferences(con);
Thread t = new Thread() {
public void run() {
try {
TwitterUtils.sendTweet(prefs, msj);
mTwitterHandler.post(mUpdateTwitterNotification);
} catch (Exception ex) {
ex.printStackTrace();
Log.d("dhaval-->send tweet:", ex.getMessage().toString());
}
}
};
t.start();
}
/** twitter methods-------------------------- end */
}
Constants.java
package com.Background_fb_twitter;
public class Constants {
public static final String CONSUMER_KEY = "XXXXXXXX";
public static final String CONSUMER_SECRET= "XXXXXXXX";
public static final String REQUEST_URL = "https://api.twitter.com/oauth/request_token";
public static final String ACCESS_URL = "https://api.twitter.com/oauth/access_token";
public static final String AUTHORIZE_URL = "https://api.twitter.com/oauth/authorize";
public static final String OAUTH_CALLBACK_SCHEME = "x-oauthflow-twitter";
public static final String OAUTH_CALLBACK_HOST = "callback";
public static final String OAUTH_CALLBACK_URL = OAUTH_CALLBACK_SCHEME + "://" + OAUTH_CALLBACK_HOST;
}
答案 0 :(得分：0)
问题是，你在这一行上遇到了NullPointerException，
String st = get_token__(con);
这里String st似乎是null。这是因为，方法get_token__(con);返回空值。
如果您查看此方法，您将从共享首选项中获取值，但作为默认值，您将获得null，
private static String get_token__(Context con) {
// TODO Auto-generated method stub
SharedPreferences sharedPreferences = con.getSharedPreferences(KEY,
Context.MODE_PRIVATE);
return sharedPreferences.getString(TOKEN, null); // This returns null..
}
由于String st为null，因此length（）无法执行并抛出NullPointerException。
答案 1 :(得分：0)
更改此方法：如果您使用此代码登录Twitter，只需检查日志即可获得访问令牌。
private static String get_token__(Context con) {
// TODO Auto-generated method stub
SharedPreferences sharedPreferences = con.getSharedPreferences(KEY,
Context.MODE_PRIVATE);
return sharedPreferences.getString(OAuth.OAUTH_TOKEN, "");
}
如果上述方法不起作用，那么只需将access token放入prefrence n用于上述方法。