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为了避免 Android 事件监听器出现“内部类地狱”，我将监听器移动到单独的类中。以下是TextView保存日期字符串的 a 的此类侦听器之一。触摸它时，我打开 aDatePickerDialog并将所选日期值设置回TextView.

我进一步增强了这个监听器以使用 Butterknife，如下所示：

public class DateViewClickListener implements View.OnClickListener {

    private final DateTime prevDate;
    private DateTimeFormatter dateFmt;

    public DateViewClickListener(DateTime prevDate, DateTimeFormatter dateFmt) {
        this.prevDate = prevDate;
        this.dateFmt = dateFmt;
    }

    @Override
    public void onClick(View view) {
        new DatePickerDialog(view.getContext(), new DatePickerDialog.OnDateSetListener() {

            @InjectView(R.id.date)
            TextView dateView;

            @Override
            public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
                Activity activity = ActivityUtil.getParentActivity(view);
                ButterKnife.inject(this, activity.getWindow().getDecorView());
                DateTime newDate = prevDate.withDate(year, monthOfYear, dayOfMonth);
                dateView.setText(dateFmt.print(newDate));
            }
        }, prevDate.getYear(), prevDate.getMonthOfYear(), prevDate.getDayOfMonth()).show();
    }
}

ActivityUtil.getParentActivity(view)在上面的代码中使用，扫描视图的上下文层次结构并找到它的父活动。以下是它的代码：

public class ActivityUtil {

    public static Activity getParentActivity(View view) {
        Context context = view.getContext();
        return scanForActivity(context);
    }

    private static Activity scanForActivity(Context context) {
        if (context == null)
            return null;
        else if (context instanceof Activity)
            return (Activity) context;
        else if (context instanceof ContextWrapper)
            return scanForActivity(((ContextWrapper) context).getBaseContext());
        return null;
    }
}

在执行此代码时，dateView剩下的会null抛出一个NPE. 但是，当我不使用 Butterknife 时，此代码对我有用（DateViewClickListener在这种情况下，类如下）。

public class DateViewClickListener implements View.OnClickListener {

    private final DateTime prevDate;
    private DateTimeFormatter dateFmt;

    public DateViewClickListener(DateTime prevDate, DateTimeFormatter dateFmt) {
        this.prevDate = prevDate;
        this.dateFmt = dateFmt;
    }

    @Override
    public void onClick(View view) {
        new DatePickerDialog(view.getContext(), new DatePickerDialog.OnDateSetListener() {

            @Override
            public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
                Activity activity = ActivityUtil.getParentActivity(view);
                TextView dateView = (TextView) activity.findViewById(R.id.date);
                DateTime newDate = prevDate.withDate(year, monthOfYear, dayOfMonth);
                dateView.setText(dateFmt.print(newDate));
            }
        }, prevDate.getYear(), prevDate.getMonthOfYear(), prevDate.getDayOfMonth()).show();
    }
}

我的理解哪里出了问题？

4

1 回答 1

1

似乎只有Butterknife.inject()在构造函数或任何 Android 生命周期方法中存在语句时，Butterknife 注入才有效。

因此，我修改了DateViewClickListener该类以接受从中调用它的活动并将其用作 Butterknife 注入的“源”，例如：

public class DateViewClickListener implements View.OnClickListener {

    @InjectView(R.id.date)
    TextView dateView;


    private final DateTime prevDate;
    private DateTimeFormatter dateFmt;

    public DateViewClickListener(DateTime prevDate, DateTimeFormatter dateFmt, Activity contextActivity) {
        Butterknife.inject(this, contextActivity);
        this.prevDate = prevDate;
        this.dateFmt = dateFmt;
    }

    .....
}

然后像这样实例化监听器：

public class MainActivity extends ActionBarActivity {

    .....

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        ......

        date.setOnClickListener(new DateViewClickListener(paymentDate, dateFmt, this));

        ......

    }

    .....

}
于 2015-05-27T05:02:20.787 回答