getActivity()上的NullPointerException .runOnUiThread(new Runnable(){

Question

我知道有很多不同的原因,NPE但我的有点奇怪(至少对我而言).

所以我已经将我转换Activities为Fragments成功,但我的问题似乎来自显示日期的函数.当应用程序运行时,一切正常.但是只要按下后退按钮.应用程序强制关闭,然后在日志中它说我正在NullPointerException第102行.所以看看代码,我对此进行了研究但很遗憾没有得到任何结果.

这是按下后退按钮时出现错误的行.

getActivity().runOnUiThread(new Runnable(){

此外,我已经尝试禁用后退按钮(因为我正在构建一个启动器,它不需要).但它似乎没有奏效.

这是整个日期显示方法/功能的代码.

// (Calendar) Date function - Displays dateview on Card
final boolean keepRunning1 = true;
Thread thread_two = new Thread(){
    @Override
    public void run(){

        while(keepRunning1){

            // Make the thread wait half a second. If you want...
            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                Toast.makeText(getActivity().getApplicationContext(), "Default Signature Fail", Toast.LENGTH_LONG).show();
                e.printStackTrace();
            }

                getActivity().runOnUiThread(new Runnable(){
                @Override
                public void run(){
                    TextView date = (TextView) getView().findViewById(R.id.date);
                    date.setText(DateUtils.formatDateTime(getActivity().getBaseContext(), System.currentTimeMillis(),DateUtils.FORMAT_SHOW_WEEKDAY | DateUtils.FORMAT_SHOW_DATE | DateUtils.FORMAT_SHOW_YEAR));
                }
            });
        }
    }
};

thread_two.start();

感谢您的时间,希望您可以了解我做错了什么.

Logcat -

05-23 21:17:33.216: E/AndroidRuntime(6906): java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.app.FragmentActivity.runOnUiThread(java.lang.Runnable)' on a null object reference
05-23 21:17:33.216: E/AndroidRuntime(6906):     at com.activelauncher.fragments.UtilsFragment$2.run(UtilsFragment.java:102)

Answer 1

我几乎可以肯定,这是在线程完成其工作但活动不再可见时引起的.

您应该检查getActivity()调用是否返回null,并且...

要对代码应用更正,请查看以下内容:

// (Calendar) Date function - Displays dateview on Card
final boolean keepRunning1 = true;
Thread thread_two = new Thread(){

@Override
public void run(){

    while(keepRunning1){

        // Make the thread wait half a second. If you want...
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            Toast.makeText(getActivity().getApplicationContext(), "Default Signature                         Fail", Toast.LENGTH_LONG).show();
            e.printStackTrace();
        }

        // here you check the value of getActivity() and break up if needed
        if(getActivity() == null)
            return;

        getActivity().runOnUiThread(new Runnable(){
        @Override
        public void run(){
           TextView date = (TextView) getView().findViewById(R.id.date);
           date.setText(DateUtils.formatDateTime(getActivity().getBaseContext(), System.currentTimeMillis(),DateUtils.FORMAT_SHOW_WEEKDAY | DateUtils.FORMAT_SHOW_DATE | DateUtils.FORMAT_SHOW_YEAR));
           }
         });
    }
}
};thread_two.start();

Answer 2

按下后,后台线程仍在运行.当线程到达getActivity().runOnUiThread()代码时,活动不再存在.检查活动是否仍然存在如下:

if (getActivity() != null) {
        getActivity().runOnUiThread(new Runnable(){
                @Override
                public void run(){
                    TextView date = (TextView) getView().findViewById(R.id.date);
                    date.setText(DateUtils.formatDateTime(getActivity().getBaseContext(), System.currentTimeMillis(),DateUtils.FORMAT_SHOW_WEEKDAY | DateUtils.FORMAT_SHOW_DATE | DateUtils.FORMAT_SHOW_YEAR));
            }
        });
}

Answer 3

放

if(getActivity() == null)
        return;

在getActivity().runOnUiThread(new Runnable(){此之前,当后退按钮关闭且您Thread仍在运行时,它将检查调用是否Activity仍然存在.

如果没有,它会return.

Answer 4

NPE的原因是您的线程未绑定到片段生命周期.片段从其托管活动中分离后,getActivity()返回null.

作为一种解决方案,请考虑完全删除线程,并在UI线程上使用postDelayed()on Handler来发布Runnable在延迟后执行所需更新的s.

Answer 5

试试这个吧

TextView date = (TextView) getView().findViewById(R.id.date);

是日期为空或不检查

if(date !=null){
                    date.setText(DateUtils.formatDateTime(getActivity().getBaseContext(), System.currentTimeMillis(),DateUtils.FORMAT_SHOW_WEEKDAY | DateUtils.FORMAT_SHOW_DATE | DateUtils.FORMAT_SHOW_YEAR));
}