小编jay*_*i93的帖子

这是我的偏好活动:

package com.example.hms.test;

import android.os.Bundle;
import android.preference.PreferenceActivity;

public class PrefsActivity extends PreferenceActivity {

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.prefs);
    }

}

在这里,我想显示一个带有名称设置的操作栏和一个回到主页的后退按钮

我需要帮助来解决与使用 HSQLDB 从数据库中提取数据相关的问题。我收到错误：

java.sql.SQLException: invalid cursor state: identifier cursor not positioned on row in UPDATE, DELETE, SET, or GET statement: ; ResultSet is empty
    at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source)
    at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source)
    at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source)
    at org.hsqldb.jdbc.JDBCResultSet.getCurrent(Unknown Source)
    at org.hsqldb.jdbc.JDBCResultSet.getColumnInType(Unknown Source)
    at org.hsqldb.jdbc.JDBCResultSet.getString(Unknown Source)
    at org.hsqldb.jdbc.JDBCResultSet.getString(Unknown Source)
    at DBactionSearch.actionPerformed(DBactionSearch.java:109)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source) …

我无法解码logcat报告.我正在学习android并尝试在单个应用程序中实现intent,toast和custom toast.

据我所知,我做得对.我正在附加logcat跟踪.

FATAL EXCEPTION: main
Process: com.bt4u.customtoast, PID: 24490
Theme: themes:{default=overlay:com.rr.neptune, iconPack:system, fontPkg:com.rr.neptune, com.android.systemui=overlay:com.rr.neptune, com.android.systemui.navbar=overlay:com.rr.neptune}
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bt4u.customtoast/com.bt4u.customtoast.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2450)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2520)
at android.app.ActivityThread.access$900(ActivityThread.java:153)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1363)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5466)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.bt4u.customtoast.MainActivity.onCreate(MainActivity.java:21)
at android.app.Activity.performCreate(Activity.java:6251)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2403)
at …