这个问题在这里已有答案:
即时尝试进行查询,但显示错误 . 这是我的代码
public String c(){
objBD = new Bd(nContext, "Laboratorios", null, 1);
db = objBD.getReadableDatabase();
Cursor c=db.rawQuery("SELECT * FROM Laboratorios WHERE ID = (SELECT MAX(ID) FROM Laboratorios);", null);
if(c!=null) {
while (c.moveToNext()) {
String iLab = c.getString(c.getColumnIndex("Descripcion"));
//.add(iLab);
return iLab;
}
}
return null;
}
这是我想要显示它的活动
protected void onCreate(Bundle savedInstanceState) {
TextView Lab=(TextView)findViewById(R.id.lab_con);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_consulta);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
ConexionBD O1=new ConexionBD(this);
O1.c();
Lab.setText(O1);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
/*String texto ="bien";
Toast toast = Toast.makeText(this, texto, Toast.LENGTH_LONG);
toast.show();
Intent i =new Intent(this,Labs.class);
startActivity(i);*/
}
public void salir (View view){
String texto ="Se ha guardado su registro";
Toast toast = Toast.makeText(this, texto, Toast.LENGTH_LONG);
toast.show();
Intent salida=new Intent( Intent.ACTION_MAIN); //Llamando a la activity principal
finish();
}
这是错误
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
我试图在空白活动中做到这一点,但总是有错误,谢谢你的帮助 .
这是错误
java.lang.RuntimeException:无法启动活动ComponentInfo {com.example.oscar.app/com.example.oscar.app.consulta}:java.lang.NullPointerException:尝试调用虚方法'void android.support.design .widget.FloatingActionButton.setOnClickListener(android.view.View $ OnClickListener)”上在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)在android.app.ActivityThread.handleLaunchActivity空对象引用(ActivityThread.java:2707 )维持在安卓android.app.ActivityThread.-wrap12(ActivityThread.java)在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1460)在android.os.Handler.dispatchMessage(Handler.java:102) . os.Looper.loop(Looper.java:154)位于com.android.internal.os的java.lang.reflect.Method.invoke(Native Method)的android.app.ActivityThread.main(ActivityThread.java:6077) . ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:865)在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)产生的原因:java.lang.NullPoin terException:尝试在上com.example.oscar.app.consulta.onCreate(CONSULTA空对象引用调用虚拟方法“无效android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View $ OnClickListener)” . 的java:31)在android.app.Activity.performCreate(Activity.java:6664)在android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)在android.app.ActivityThread.handleLaunchActivity在android.os(ActivityThread.java:2707)在android.app.ActivityThread.-wrap12(ActivityThread.java)在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1460) . Handler.dispatchMessage(Handler.java:102)位于android.app.Looper.loop(Looper.java:154)的android.app.ActivityThread.main(ActivityThread.java:6077),位于java.lang.reflect.Method.invoke (本地方法)位于com.android.internal.os.ZygoteInit的com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:865) . 主要(ZygoteInit.java:755)
1 回答
问题似乎如下
您似乎正在尝试查找尚未在屏幕上绘制的视图 . 尝试将行移动到活动布局之后,如下所示: