java - 在 Helper 类中使用 ApplicationContext

Question

我想做什么

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我正在尝试创建一个完全在 Helperclass 中处理的登录，以保持代码简单。

为此，我创建了一个具有我需要的所有功能的helperclass，现在的问题是我总是得到一个NullPointer-Exception，可能是因为获取应用程序上下文。

问题

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那么我需要在我的代码中更改什么才能使其正常工作。下面提供了代码。如果您有很棒的教程或其他内容，请提供给我。我真的很喜欢自己做这件事。

代码

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LoginActivity.class

package de.ivocore;


public class LoginActivity extends Activity {

    private DBAdapter mDbHelper;

    private LoginHelper login = new LoginHelper();



    **/
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);

        mDbHelper = new DBAdapter(this);
        mDbHelper.open();
        mDbHelper.close();

        // Text-Felder
        final EditText user = (EditText) findViewById(R.id.edt_username);
        final EditText pwd = (EditText) findViewById(R.id.edt_password);

        // Button
        Button loginbt = (Button) findViewById(R.id.bt_login);

        // OnClickListner für den Button definieren
        loginbt.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {

                // Eingegebener Username und Passwort auslesen
                final String usertxt = user.getText().toString();
                final String pwdtxt = pwd.getText().toString();
                Log.d("User", usertxt);
                Log.d("PWD", pwdtxt);

                checkLoginData(usertxt, pwdtxt);
            }
        });

    }   

public void checkLoginData(final String username, final String password){

    boolean user, pass;

    if (username.length() < 6){
        user = false;
    }else {
        user = true;
    }

    if (password.length() < 6){
        pass = false;
    }else {
        pass = true;
    }

    int val = 0;
    if (user) val |= 0x1;
    if (pass) val |= 0x2;

    switch (val){
    case 0:
        login.loginFalse(getApplicationContext(),"Username und Passwort müssen mindestens 6 Zeichen haben");

    break;

    case 1:
        login.loginFalse(getApplicationContext(),"Passwort muss mindestens 6 Zeichen haben");
    break;

    case 2:
        login.loginFalse(getApplicationContext(),"Username muss mindestens 6 Zeichen haben");
    break;

    case 3:
        login.doLogin(getApplicationContext(),username, password);
    }

}
}

LoginHelper.class

package de.ivocore.firstboot;


public class LoginHelper {

    private static final String PREFS_NAME = "de.ivocore.firstboot.PREF_NAME";
    private static final String PREFS_USER = "de.ivocore.firstboot.PREF_USER";
    private static final String PREF_FIRSTBOOT = "de.ivocore.firstboot.FIRSTBOOT";

    ProgressDialog progressDialog;
    private static SharedPreferences mPrefs;
    boolean first;
    Context test;

    // Handlet die Message aus dem Thread
    private Handler handler = new Handler() {

        public void handleLogin(Message msg) {

            switch(msg.what){
            case 0: {
                progressDialog.dismiss();
                Intent i = new Intent(test, MainActivity.class);
                test.startActivity(i);

            } break;

            case 1:{
                progressDialog.dismiss();
                String text = "Username oder Passwort inkorrekt";
                loginFalse(test, text);
            } break;
        }

        }
    };

    /**
     * Hier wird ein AlertDialog erzeugt welcher zurück gibt ob was am Login
     * falsch war.
     * 
     * @param ctx
     *            Context der Klasse
     * @param text
     *            Text der ausgegeben werden soll
     */
    public void loginFalse(Context ctx, String text) {

        AlertDialog alertDialog;
        alertDialog = new AlertDialog.Builder(ctx)
                .setMessage(text)
                .setTitle("Login inkorrekt")
                .setCancelable(true)
                .setNeutralButton(android.R.string.cancel,
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog,
                                    int whichButton) {
                            }
                        }).show();
    }

    public void doLogin(final Context ctx, final String username,
            final String password) {

        progressDialog = ProgressDialog.show(ctx, "Login", "Bitte warten...");

        Thread t = new Thread() {
            @Override
            public void run() {

                String URL = "http://LOGINURL (NotForYourEyes)"

                DefaultHttpClient client = new DefaultHttpClient();
                HttpResponse response;


                try {
                    //Firstboot überprüfung

                    HttpPost post = new HttpPost(URL);
                    StringEntity se = new StringEntity("username=" + username
                            + "&password=" + password);
                    post.setEntity(se);
                    post.addHeader("Content-Type",
                            "application/x-www-form-urlencoded"); // Dieser
                                                                    // Header is
                                                                    // von curl
                                                                    // -d Befehl
                                                                    // abgeleitet
                    response = client.execute(post);

                    int statuscode = response.getStatusLine().getStatusCode();

                    switch (statuscode) {

                    case 200:

                        if (response != null) {

                            StringBuilder sb = new StringBuilder();
                            BufferedReader rd = new BufferedReader(
                                    new InputStreamReader(response.getEntity()
                                            .getContent()));

                            String line;
                            while ((line = rd.readLine()) != null) {
                                sb.append(line + "\n");
                            }

                            String result;
                            result = sb.toString();

                            // User-Id auslesen
                            final String uid;
                            JSONObject holder = new JSONObject(result);
                            uid = holder.getString("id");
                            Log.d("JSON-Response", uid);

                            String token = "test-token";


                             SharedPreferences logindata = ctx.getSharedPreferences(PREFS_USER, 0);
                             SharedPreferences.Editor editor = logindata.edit(); editor.clear();
                             editor.putString("userid", uid);
                             editor.putString("token", token);
                             editor.commit();


                            handler.sendEmptyMessage(0);
                        }
                        break;

                    case 500:

                        handler.sendEmptyMessage(1);

                        break;

                    }

                } catch (Exception e) {
                    e.printStackTrace();
                    Log.e("DataHandler", "URLConnection-Error" + e);
                }
            }
        };
        t.start();
    }

    /**
     * Mit dieser Methode wird heraussgesucht ob der erste Login bereits
     * geschehen ist
     * 
     * @return firstboot
     */
    private boolean getFirstboot() {
        boolean firstboot = mPrefs.getBoolean(PREF_FIRSTBOOT, first);
        return firstboot;
    }

    /**
     * Hier wird die Variabel auf true gesetzt, falls der Firstboot bereits
     * passiert ist.
     * 
     * @param first
     */
    private static void setFirstboot(boolean first) {
        mPrefs.edit().putBoolean(PREF_FIRSTBOOT, first).commit();
    }

}

---

日志:

   03-14 08:12:53.464: E/AndroidRuntime(9462): android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.view.ViewRootImpl.setView(ViewRootImpl.java:519)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:279)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:193)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.view.WindowManagerImpl$CompatModeWrapper.addView(WindowManagerImpl.java:118)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.app.Dialog.show(Dialog.java:274)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.app.AlertDialog$Builder.show(AlertDialog.java:932)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at de.ivocore.firstboot.LoginHelper.loginFalse(LoginHelper.java:80)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at de.ivocore.LoginActivity.checkLoginData(LoginActivity.java:120)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at de.ivocore.LoginActivity$1.onClick(LoginActivity.java:92)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.view.View.performClick(View.java:3480)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.view.View$PerformClick.run(View.java:13983)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.os.Handler.handleCallback(Handler.java:605)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.os.Handler.dispatchMessage(Handler.java:92)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.os.Looper.loop(Looper.java:137)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at android.app.ActivityThread.main(ActivityThread.java:4340)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at java.lang.reflect.Method.invokeNative(Native Method)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at java.lang.reflect.Method.invoke(Method.java:511)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-14 08:12:53.464: E/AndroidRuntime(9462):     at dalvik.system.NativeStart.main(Native Method)

如果您需要更多代码或更详细的信息，请将其写在下面的评论中。

Answer 1

getApplicationContext(); 

对于对话框或任何其他 UI 更改功能，您必须从您的 Activity 中传递它。

getApplicationContext() 应该仅在不涉及 UI 时使用(加载资源、prefs、.. 等)。