Question

我有以下代码：

final LinkedHashMap<String, Line> trainLinesMap = MetraRail.myDbHelper.getTrainLinesHashMap();

// Create an array of proper line names for the listview adapter.
String[] train_lines_long_names = new String[trainLinesMap.size()];

Iterator<Entry<String, Line>> it = trainLinesMap.entrySet().iterator();
for (int i = 0; it.hasNext(); i++) {
    Map.Entry<String, Line> pairs = (Map.Entry<String, Line>) it.next();
    train_lines_long_names[i] = (String) pairs.getKey();
}

// Override the default list adapter so we can do 2 things: 1) set custom background colors
// on each item, and 2) so we can more easily add onclick handlers to each item.
listview.setAdapter(
new ArrayAdapter<String>(this, R.layout.select_line_row_layout,
        R.id.select_line_line_label, train_lines_long_names) {

                @Override
                public View getView(int position, View convertView, ViewGroup parent) {
                    TextView textView = (TextView) super.getView(position, convertView, parent);

                    // Change the background color of each item in the list.
                    final String line_label_long = textView.getText().toString();
                    final int line_color = trainLinesMap.get(line_label_long).getColorInt();
                    textView.setBackgroundColor(line_color);

                    // Add onclick handlers to each item.
                    textView.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            Intent i = new Intent();
                            i.setClassName("garrettp.metrarail", 
                                    "garrettp.metrarail.screens.SelectStations");
                            i.putExtra("garrettp.metrarail.line.short", 
                                    trainLinesMap.get(line_label_long).getShortName());
                            i.putExtra("garrettp.metrarail.line.long", line_label_long);
                            i.putExtra("garrettp.metrarail.line.color", line_color);
                            startActivity(i);
                        }
                    });

                    return textView;
                }
            });

在这一行：

final int line_color = trainLinesMap.get(line_label_long).getColorInt();

我收到NullPointerException：

10-26 16:10:35.922: E/AndroidRuntime(1785): java.lang.NullPointerException
10-26 16:10:35.922: E/AndroidRuntime(1785):     at garrettp.metrarail.screens.SelectLine$1.getView(SelectLine.java:74)

这是为什么？在调试器中，我已经验证了trainLinesMap已正确初始化并填充了值。它在第一个for循环中成功迭代，所以我知道那里有值。但是，当从我的匿名内部类访问LinkedHashMap时，它始终为null。

我能够从这个内部类访问一个String数组，为什么我不能访问LinkedHashMap？

Answer 1

我通过分手来解决这个问题：

final int line_color = trainLinesMap.get(line_label_long).getColorInt();

成：

Line thisLine = trainLinesMap.get(line_label_long);
final int line_color = thisLine.getColorInt();

我不确定为什么会这样，但我不再获得NullPointerExceptions。

无法在内部类中访问LinkedHashMap

1 个答案: