Android NullPointerException in custom view access

问题

I have created a custom view name StepView . Here is the code for StepView.

public class StepView extends LinearLayout {

    private Context cont;
    private LinearLayout stepHolder;

    public StepView(Context context, AttributeSet attrs) {
        super(context);
        // TODO Auto-generated constructor stub
        LayoutInflater.from(context).inflate(R.layout.stepview, this, true);
        stepHolder = (LinearLayout) findViewById(R.id.stepHolder);

        cont = context;
    }

    public void addStep(String title, int drawableId, View.OnClickListener stepAction){

        View step = LayoutInflater.from(cont).inflate(R.layout.step, this, true);
        TextView txtText = (TextView) step.findViewById(R.id.txtText);
        ImageView imgStep = (ImageView) step.findViewById(R.id.imgStep);

        txtText.setText(title);
        imgStep.setImageResource(drawableId);

        stepHolder.addView(step);
    }


}

It is the code for stepview.xml.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    <LinearLayout
        android:id="@+id/stepHolder"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal" >

    </LinearLayout>

</LinearLayout>

step.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ImageView 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imgStep"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/txtText">

    </TextView>

</LinearLayout>

Now I used the XML in main layout.

<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android" >

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:orientation="horizontal" >
 ..................
     </LinearLayout>

    <com.orthokeys.view.StepView
        android:id="@+id/stepMenu"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" >
    </com.orthokeys.view.StepView>

</merge>

I have cheched that it is appearing properly. But when I add the following code it is giving NullPointerException.

StepView stepMenu = (StepView) findViewById(R.id.stepMenu);
stepMenu.addStep("Picture", R.drawable.step01, null);

I have checked that stepMenu is giving null.

Whatis the problem in my code?

回答1:

I solved the prob...change the code in constructor of StepView Class

public StepView(Context context, AttributeSet attrs) {
  super(context, attrs);
  ....................
}

回答2:

You are not showing the full code block where you get the error, but it looks like you may have forgotten to use setContentView(R.layout.main_layout); to set the layout in use.

来源：https://stackoverflow.com/questions/12915856/android-nullpointerexception-in-custom-view-access

标签

android

android-layout

nullpointerexception

custom-view