我是安卓新手。我在我的应用程序中集成了 google plus 登录。但它在 mConnectionResult.hasResolution 处显示空指针异常 这是我的代码

 btnSignIn = (SignInButton) findViewById(R.id.btn_sign_in);
    btnSignIn.setOnClickListener(this);
    mGoogleApiClient = new GoogleApiClient.Builder(this)
            .addConnectionCallbacks(this)
            .addOnConnectionFailedListener(this).addApi(Plus.API)
            .addScope(Plus.SCOPE_PLUS_LOGIN).build();
}


@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    callbackManager.onActivityResult(requestCode, resultCode, data);

    if (requestCode == RC_SIGN_IN) {
        if (resultCode != RESULT_OK) {
            mSignInClicked = false;
        }

        mIntentInProgress = false;

        if (!mGoogleApiClient.isConnecting()) {
            mGoogleApiClient.connect();
        }
    }
}

protected void onStart() {
    super.onStart();
    mGoogleApiClient.connect();
}

protected void onStop() {
    super.onStop();
    if (mGoogleApiClient.isConnected()) {
        mGoogleApiClient.disconnect();
    }
}

/**
 * Method to resolve any signin errors
 */
private void resolveSignInError() {
    if (mConnectionResult.hasResolution()) {
        try {
            mIntentInProgress = true;
            mConnectionResult.startResolutionForResult(this, RC_SIGN_IN);
        } catch (IntentSender.SendIntentException e) {
            mIntentInProgress = false;
            mGoogleApiClient.connect();
        }
    }
}

@Override
public void onConnectionFailed(ConnectionResult result) {
    if (!result.hasResolution()) {
        GooglePlayServicesUtil.getErrorDialog(result.getErrorCode(), this,
                0).show();
        return;
    }

    if (!mIntentInProgress) {
        // Store the ConnectionResult for later usage
        mConnectionResult = result;

        if (mSignInClicked) {
            // The user has already clicked 'sign-in' so we attempt to
            // resolve all
            // errors until the user is signed in, or they cancel.
            resolveSignInError();
        }
    }

}

@Override
public void onConnected(Bundle arg0) {
    mSignInClicked = false;
    if (temp == true) {
        type = "2";
        Toast.makeText(this, "User is connected!", Toast.LENGTH_LONG).show();

        Intent i = new Intent(RegisterSkipActivity.this, MainActivity.class);
        i.putExtra("Login", type);
        startActivity(i);
        temp = false;
    }

}


@Override
public void onConnectionSuspended(int arg0) {
    mGoogleApiClient.connect();
    //updateUI(false);
}

@Override
public void onClick(View v) {

    // Signin button clicked
    signInWithGplus();
    temp = true;

}

/**
 * Sign-in into google
 */
private void signInWithGplus() {
    if (!mGoogleApiClient.isConnecting()) {
        mSignInClicked = true;
        resolveSignInError();
    }
}

resolveSignInError() 中这一行的空指针异常

  if (mConnectionResult.hasResolution()) 

请帮帮我。这是 Logcat

  java.lang.NullPointerException
        at com.techieweb.solutions.pickeronline.RegisterSkipActivity.resolveSignInError(RegisterSkipActivity.java:214)
        at com.techieweb.solutions.pickeronline.RegisterSkipActivity.signInWithGplus(RegisterSkipActivity.java:284)
        at com.techieweb.solutions.pickeronline.RegisterSkipActivity.onClick(RegisterSkipActivity.java:273)
        at com.google.android.gms.common.SignInButton.onClick(Unknown Source)
        at android.view.View.performClick(View.java:4439)
        at android.widget.Button.performClick(Button.java:139)
        at android.view.View$PerformClick.run(View.java:18395)
        at android.os.Handler.handleCallback(Handler.java:725)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:176)
        at android.app.ActivityThread.main(ActivityThread.java:5317)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
        at dalvik.system.NativeStart.main(Native Method)

最佳答案

您使用的是旧的 Google 签名方法(播放服务 8.3 之前)。如果您构建了一个使用旧的 Sign-In with Google 的应用程序，您将构建一个尝试连接到 GoogleApiClient 的应用程序。此时，用户会看到一个帐户选择器和/或一个权限对话框，这两者都会触发连接失败。

您必须处理这些连接失败才能登录。连接 GoogleApiClient 后，用户将被视为已登录并可以授予权限。

引用这个codelab by google 处理此类故障并使用该方法实现登录。

现在最好的选择是试用新的 Google-Sign In with play services 8.3。它更加顺畅，并自动为您处理此类连接失败。

引用new Google-Sign In .

另请查看官方 android 开发者博客以获取更多信息。

Android Developers Blog- Identity #1

Android Developers Blog- Identity #2

关于android - google plus登录中的空指针异常，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/34147975/