相关疑难解决方法(0)

在我的媒体播放器中,我从sdcard播放一首歌.它显示错误为NullPointerException:println在android中需要一条消息e.我试了很久但我不知道原因.请帮助我.

码:

    try {
        mediaPlayer = new  MediaPlayer();
        mediaPlayer.setDataSource("/sdcard/t1.mp3");
        seek.setMax(mediaPlayer.getDuration());
        mediaPlayer.prepare();
        mediaPlayer.start();
        mediaPlayer.setOnCompletionListener(this);          
    }
    catch(Exception ex){
        Log.e("sdcard-err2:",ex.getMessage());  //  null pointer exception : println needs a message 
    }  

原木猫:

     05-16 19:27:54.491: ERROR/AndroidRuntime(6889): Caused by: java.lang.NullPointerException: println needs a message
     05-16 19:27:54.491: ERROR/AndroidRuntime(6889):     at android.util.Log.println(Native Method)
     05-16 19:27:54.491: ERROR/AndroidRuntime(6889):     at android.util.Log.e(Log.java:208)
     05-16 19:27:54.491: ERROR/AndroidRuntime(6889):     at com.seek.bar.media3.onCreate(media3.java:43)
     05-16 19:27:54.491: ERROR/AndroidRuntime(6889):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
     05-16 19:27:54.491: ERROR/AndroidRuntime(6889):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)
     05-16 19:27:54.491: ERROR/AndroidRuntime(6889):     ... 11 more

我尝试登录时,我的应用程序出现问题.

事实上,如果我注册(如果remerberMe isChecked()注册操作上的复选框,在下次连接时显示主要活动,否则显示登录活动),它可以正常工作.

但是,Login在注册操作后调用下一个连接时,Activity不起作用.

登录活动

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);
        setTitle(R.string.loginTitle);

        // Importing all assets like buttons, text fields
        inputUsername = (EditText) findViewById(R.id.username_value);
        inputPassword = (EditText) findViewById(R.id.password_value);
        btnLogin = (Button) findViewById(R.id.loginButton);
        btnExit = (Button) findViewById(R.id.exitButton);
        btnLinkToRegister = (Button) findViewById(R.id.btnLinkToRegister);
        rememberMe = (CheckBox) findViewById(R.id.rememberNameRegister);

        // Login button Click Event
        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                LoginAction();
            }
        });

        // Link to Register Screen
        btnLinkToRegister.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) { …