动态添加行到自定义 listView （每行有多个 Strings ）

Question

My last app had a custom layout, listview , I could add items and those items would appear in the listview . Now, I want to make an app, also with custom layout, listview , but every row exist of 3 different Strings, so before my app will give a new row, you have to type in 3 different strings and than he will make a new row. But this doesn't work... Can you help me where I made a mistake? thanks already!

Main Activity

ListView ListView ;

EditText editTextMerk ;
EditText editTextBeschrijving ;
EditText editTextKm ;

Button voegToe ;

ArrayList<String> merk;
ArrayList<String> beschrijving ;
ArrayList<String> km ;

CustomAdapter adapter ;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    editTextMerk = (EditText) findViewById(R.id.editTextMerk) ;
    editTextBeschrijving = (EditText) findViewById(R.id.editTextBeschrijving) ;
    editTextKm = (EditText) findViewById(R.id.editTextKm) ;

    ListView =(ListView) findViewById(R.id.Listview) ;
    adapter = new CustomAdapter(this , merk , beschrijving  , km ) ;
    ListView.setAdapter(adapter);

    voegToe.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {


            merk.add(editTextMerk.getText().toString()) ;
            beschrijving.add(editTextBeschrijving.getText().toString()) ;
            km.add(editTextKm.getText().toString()) ;

            adapter.notifyDataSetChanged();
        }
    });

}

This is my CustomAdapter Class

LayoutInflater mInflater ;

ArrayList<String> merk;
ArrayList<String> beschrijving ;
ArrayList<String> km ;

public CustomAdapter(Context c, ArrayList<String> merk, ArrayList<String> beschrijving, ArrayList<String> km) {

    this.merk = merk;
    this.beschrijving = beschrijving;
    this.km = km;

    mInflater = (LayoutInflater) c.getSystemService(Context.LAYOUT_INFLATER_SERVICE) ;
}

@Override
public int getCount() {
    return merk.size();
}

@Override
public Object getItem(int position) {
    return merk.get(position);
}

@Override
public long getItemId(int position) {
    return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    View v = mInflater.inflate(R.layout.layout_row, null) ;

    TextView brand  = (TextView) v.findViewById(R.id.textViewMerk) ;
    TextView discription = (TextView) v.findViewById(R.id.textViewBeschrijving) ;
    TextView distance = (TextView) v.findViewById(R.id.textViewKm) ;

    brand.setText(merk.get(position));
    discription.setText(beschrijving.get(position));
    distance.setText(km.get(position));


    return v;
}

Answer 1

There are two problems:

1. You are not finding voegToe in onCreate() method. Trying to call setOnClickListener() on a null object produces NPE.
2. You are not initializing your lists. Passing them while they are null would produce NPE when getCount() called when you try to setAdapter() to your ListView.

Therefore, you need to update your Activity as follows:

ListView listView;

...

ArrayList<String> merk = new ArrayList<>();
ArrayList<String> beschrijving = new ArrayList<>();
ArrayList<String> km = new ArrayList<>();

...

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    editTextMerk = (EditText) findViewById(R.id.editText1);
    editTextBeschrijving = (EditText) findViewById(R.id.editText2);
    editTextKm = (EditText) findViewById(R.id.editText3);
    voegToe = (Button) findViewById(R.id.button);

    listView = (ListView) findViewById(R.id.list);
    adapter = new CustomAdapter(this, merk, beschrijving, km);
    listView.setAdapter(adapter);

    voegToe.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            merk.add(editTextMerk.getText().toString());
            beschrijving.add(editTextBeschrijving.getText().toString());
            km.add(editTextKm.getText().toString());
            adapter.notifyDataSetChanged();
        }
    });
}