检查数据库是否为空
我正在尝试检查一个sqlite数据库是否为空使用
public boolean chkDB(){
boolean chk = false;
Cursor mCursor = db.rawQuery("SELECT * FROM " + DATABASE_TABLE, null);
if (mCursor != null){
mCursor.moveToFirst();
if (mCursor.getInt(0) == 0){
chk = false;
}
}else{
chk = true;
}
return chk;
}
但每次我调用该方法时，我都会得到空指针异常
我的Logcat显示了这一点
06-28 22:35:19.519: E/AndroidRuntime(441): at com.android.id.DBAdapter.chkDB(DBAdapter.java:82)
06-28 22:58:06.269: E/AndroidRuntime(621): FATAL EXCEPTION: main
06-28 22:58:06.269: E/AndroidRuntime(621): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.id/com.android.id.MainActivity}: java.lang.NullPointerException
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.os.Handler.dispatchMessage(Handler.java:99)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.os.Looper.loop(Looper.java:123)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread.main(ActivityThread.java:4627)
06-28 22:58:06.269: E/AndroidRuntime(621): at java.lang.reflect.Method.invokeNative(Native Method)
06-28 22:58:06.269: E/AndroidRuntime(621): at java.lang.reflect.Method.invoke(Method.java:521)
06-28 22:58:06.269: E/AndroidRuntime(621): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
06-28 22:58:06.269: E/AndroidRuntime(621): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
06-28 22:58:06.269: E/AndroidRuntime(621): at dalvik.system.NativeStart.main(Native Method)
06-28 22:58:06.269: E/AndroidRuntime(621): Caused by: java.lang.NullPointerException
06-28 22:58:06.269: E/AndroidRuntime(621): at com.android.id.DBAdapter.chkDB(DBAdapter.java:82)
06-28 22:58:06.269: E/AndroidRuntime(621): at com.android.id.MainActivity.enterDB(MainActivity.java:66)
06-28 22:58:06.269: E/AndroidRuntime(621): at com.android.id.MainActivity.onCreate(MainActivity.java:23)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
06-28 22:58:06.269: E/AndroidRuntime(621): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
06-28 22:58:06.269: E/AndroidRuntime(621): ... 11 more
mCursor.moveToFirst()返回是否成功找到元素的布尔值。 用它移动到游标的第一行，同时检查一行是否真的存在。
Cursor mCursor = db.rawQuery("SELECT * FROM " + DATABASE_TABLE, null);
Boolean rowExists;
if (mCursor.moveToFirst())
{
// DO SOMETHING WITH CURSOR
rowExists = true;
} else
{
// I AM EMPTY
rowExists = false;
}
无论是否存在，您都试图访问游标中的一行。
if(mCursor.getCount() == 0)
应该做的伎俩
if(mCursor!=null&&mCursor.getCount>0)