共享偏好正在冻结我的应用 - Android移动应用

Question

所以我正在尝试创建一个共享首选项，该应用程序运行良好，然后突然间它崩溃了。

我已经把它归结为破坏代码的确切行，我不确定如何修复它。

有什么建议吗？

这是我目前的代码：

    public class studentEmail extends Activity {
    private WebView mWebview;

    public static final String PREFS_NAME = "MyPrefsFile";

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
   setContentView(R.layout.student_email) ;



final SharedPreferences preferences = getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE);

mWebview = new WebView(this);


        final EditText emEdit   = (EditText)findViewById(R.id.editEmail);
        final EditText passEdit   = (EditText)findViewById(R.id.editPass);

if(preferences.getString("username", null).isEmpty() && preferences.getString("password", null).isEmpty())
    {

        mWebview  = new WebView(this);

        mWebview.getSettings().setJavaScriptEnabled(true); // enable javascript

        final Activity activity = this;

        mWebview.setWebViewClient(new WebViewClient() {
            public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
                Toast.makeText(activity, description, Toast.LENGTH_SHORT).show();
            }
        });

Toast.makeText(getApplicationContext(), "Preference is empty :)", Toast.LENGTH_SHORT).show();

        TextView text = (TextView)findViewById(R.id.textView1);

        TextView textEmail = (TextView)findViewById(R.id.textViewEmail);
        TextView textPass = (TextView)findViewById(R.id.textViewPass);
        TextView textTitle = (TextView)findViewById(R.id.textViewTitle);
        text.setTypeface(null, Typeface.BOLD_ITALIC);
        textEmail.setTypeface(null, Typeface.BOLD_ITALIC);
        textPass.setTypeface(null, Typeface.BOLD_ITALIC);
        textTitle.setTypeface(null, Typeface.BOLD_ITALIC);
        text.setTextSize(android.util.TypedValue.COMPLEX_UNIT_PX,26);
        textEmail.setTextSize(android.util.TypedValue.COMPLEX_UNIT_PX,26);
        textPass.setTextSize(android.util.TypedValue.COMPLEX_UNIT_PX,26);
        textTitle.setTextSize(android.util.TypedValue.COMPLEX_UNIT_PX, 40);
        textTitle.setText("E-mail Login");
        text.setText("\n\nPlease enter your Student E-mail and Password.\n");
        textEmail.setText("E-Mail:");
        textPass.setText("\nPassword:");

        final EditText emailValidate = (EditText)findViewById(R.id.editEmail);
        final TextView emailValMsg = (TextView)findViewById(R.id.emailValidate);
        final EditText password = (EditText)findViewById(R.id.editPass);

emailValidate.addTextChangedListener(new TextWatcher() {

            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }
            public void onTextChanged(CharSequence s, int start, int before, int count) {

            }
            public void afterTextChanged(Editable s) {

                String email = emailValidate.getText().toString().trim();
                String emailPattern = "[a-zA-Z0-9._-]+@mail+\\.+itsligo+\\.+ie+";

                if (email.matches(emailPattern) && s.length() > 0)
                {
                    Toast.makeText(getApplicationContext(), "Your e-mail is now valid! :)", Toast.LENGTH_SHORT).show();
                    // or
                    emailValMsg.setText("Valid email");
                }
                else
                {
                    emailValMsg.setText("Invalid email !");
                }
            }
        });

final Button button = (Button) findViewById(R.id.loginButton);
        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {

                String email = emailValidate.getText().toString().trim();
                String emailPattern = "[a-zA-Z0-9._-]+@[a-z]+\\.+[a-z]+";

                if (emailValidate.getText().toString().trim().matches("") || password.getText().toString().trim().matches("")) {
                    if (emailValidate.getText().toString().trim().matches("") && password.getText().toString().trim().matches("")) {
                        Toast.makeText(getApplicationContext(), "Please enter an E-mail Address and Password", Toast.LENGTH_SHORT).show();
                    } else if (emailValidate.getText().toString().trim().matches("")) {
                        Toast.makeText(getApplicationContext(), "Please enter an E-mail Address", Toast.LENGTH_SHORT).show();
                    } else if (password.getText().toString().trim().matches("")) {
                        Toast.makeText(getApplicationContext(), "Please enter a Password", Toast.LENGTH_SHORT).show();
                    }
                }

else {
                    mWebview.setWebViewClient(new WebViewClient() {
                        @Override
                        public void onPageFinished(WebView view, String url) {
                            String webUrl = mWebview.getUrl();

                                    CheckBox cbox1 = (CheckBox)findViewById(R.id.checkbox_store);

                            if (cbox1.isChecked())
                            {

                            }
                            mWebview.loadUrl("javascript:(function() { " + "document.getElementById('cred_userid_inputtext').value ='" + emEdit.getText() + "';" + "})()");
                            mWebview.loadUrl("javascript:(function() { " + "document.getElementById('cred_password_inputtext').value ='" + passEdit.getText() + "';" + "})()");
                            mWebview.loadUrl("javascript:(function() { " + "document.getElementById('credentials').submit(); return false;" + "})()");
                        }
                    });

                    mWebview.loadUrl("http://login.microsoftonline.com");
                    setContentView(mWebview);
                    Toast.makeText(getApplicationContext(), "This works!", Toast.LENGTH_SHORT).show();

                }

            }
        });
    }

else
    {

        mWebview  = new WebView(this);

        mWebview.getSettings().setJavaScriptEnabled(true); // enable javascript

        final Activity activity = this;

        mWebview.setWebViewClient(new WebViewClient() {
            public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
                Toast.makeText(activity, description, Toast.LENGTH_SHORT).show();
            }
        });

        mWebview.setWebViewClient(new WebViewClient() {
            @Override
            public void onPageFinished(WebView view, String url) {
                String webUrl = mWebview.getUrl();

                mWebview.loadUrl("javascript:(function() { " + "document.getElementById('cred_userid_inputtext').value ='" + preferences.getString("username", null).toString() + "';" + "})()");
                mWebview.loadUrl("javascript:(function() { " + "document.getElementById('cred_password_inputtext').value ='" + preferences.getString("password", null).toString() + "';" + "})()");
                mWebview.loadUrl("javascript:(function() { " + "document.getElementById('credentials').submit(); return false;" + "})()");
            }
        });

mWebview.loadUrl("http://login.microsoftonline.com");
        setContentView(mWebview);
        Toast.makeText(getApplicationContext(), "Preferences have something", Toast.LENGTH_SHORT).show();

    }
}
}

错误：

02-14 19:20:06.130      632-632/com.example.PorjectStudent E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.PorjectStudent/com.example.PorjectStudent.studentEmail}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
        at android.app.ActivityThread.access$600(ActivityThread.java:130)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4745)
        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:786)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
        at dalvik.system.NativeStart.main(Native Method)

Caused by: java.lang.NullPointerException

02-14 19:20:06.130      632-632/com.example.PorjectStudent E/AndroidRuntime﹕ FATAL EXCEPTION: main
    at com.example.PorjectStudent.studentEmail.onCreate(studentEmail.java:35)
    at android.app.Activity.performCreate(Activity.java:5008)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
                at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
                at android.app.ActivityThread.access$600(ActivityThread.java:130)
                at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
                at android.os.Handler.dispatchMessage(Handler.java:99)
                at android.os.Looper.loop(Looper.java:137)
                at android.app.ActivityThread.main(ActivityThread.java:4745)
                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:786)
                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
                at dalvik.system.NativeStart.main(Native Method)
02-14 19:42:37.971      677-677/com.example.PorjectStudent E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.PorjectStudent/com.example.PorjectStudent.studentEmail}: java.lang.NullPointerException
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
    at android.app.ActivityThread.access$600(ActivityThread.java:130)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:4745)
    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:786)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
    at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.PorjectStudent.studentEmail.onCreate(studentEmail.java:39)
    at android.app.Activity.performCreate(Activity.java:5008)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
                at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
                at android.app.ActivityThread.access$600(ActivityThread.java:130)
                at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
                at android.os.Handler.dispatchMessage(Handler.java:99)
                at android.os.Looper.loop(Looper.java:137)
                at android.app.ActivityThread.main(ActivityThread.java:4745)
                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:786)
                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
                at dalvik.system.NativeStart.main(Native Method)

我真的很难过，解决方案可能很简单，但它整天都在破坏我的大脑所以我决定寻求帮助，因为我没有在几个小时内取得进展！

感谢您的帮助：）

Answer 1

您必须在setContentView(R.layout.student_email);之后立即致电super.onCreate(savedInstanceState);。你将SharedPreferences放在中间，你不能这样做。

作为一般规则，这两个句子必须是任何onCreate()方法的第一个句子（至少在Activity内）。

----编辑----

public class studentEmail extends Activity {
private WebView mWebview;

public static final String PREFS_NAME = "MyPrefsFile";

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.student_email) ;

    final SharedPreferences preferences = getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE); //This line breaks the code

    mWebview = new WebView(this);

    final EditText emEdit   = (EditText)findViewById(R.id.editEmail);
    final EditText passEdit   = (EditText)findViewById(R.id.editPass);

Answer 2

您必须始终在setContentView(R.layout...) ;之后启动自定义代码。