Question

我想将用户写入的textbox中的新项目放入DynamoDB中的现有表中。但是，我遇到了一些我不太懂的错误。以下是我的代码：

添加方法

＆＃13;

public class Add_Item
{
    private String title;
    private AmazonDynamoDBClient client;
    String tableName = "Tesis_FTSM";

    public void DynamoDBLoad() throws IOException
    {
        AWSCredentials credentials = new PropertiesCredentials(DynamoDBClient.class.getClassLoader().getResourceAsStream("AWSCredentials.properties"));
        client = new AmazonDynamoDBClient(credentials);
        client.setRegion(Region.getRegion(Regions.US_WEST_2));
    }

    public void add()
        {
          
            final EditText title = (EditText)findViewById(R.id.text1);
            String tajuk = title.getText().toString();
          
            Map<String, AttributeValue> item = new HashMap<String, AttributeValue>();

            try {
               item.put("Id", new AttributeValue().withS(tajuk));

                PutItemRequest itemRequest = new PutItemRequest().withTableName(
                        tableName).withItem(item);
                client.putItem(itemRequest);
                item.clear();

            } catch (Exception e) {
                System.err.println("Create items failed.");
                System.err.println(e.getMessage());
            }
        }

＆＃13;

MainActivity

＆＃13;

public class Task extends AsyncTask<String, Void, String> {

        @Override
        protected String doInBackground(String... params) {

            Looper.prepare();

            try
            {
                Add_Item db = new Add_Item();

                db.DynamoDBLoad();
                db.add();
                  
            } catch (Exception e)
            {
                e.printStackTrace();
            }
            Looper.myLooper().quit();
            return null;
        }
        protected void onPostExecute(String page)
        {
            //onPostExecute
        }
    }

＆＃13;

Logcat错误

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06-15 10:33:33.938  16885-17179/com.af.ftsm.testing W/System.err﹕java.lang.NullPointerException
06-15 10:33:33.938  16885-17179/com.af.ftsm.testing W/System.err﹕ at android.app.Activity.findViewById(Activity.java:1957)
06-15 10:33:33.938  16885-17179/com.af.ftsm.testing W/System.err﹕ at com.af.ftsm.testing.Add_Item.<init>(Add_Item.java:26)
06-15 10:33:33.938  16885-17179/com.af.ftsm.testing W/System.err﹕ at com.af.ftsm.testing.MainActivity$Task.doInBackground(MainActivity.java:50)
06-15 10:33:33.938  16885-17179/com.af.ftsm.testing W/System.err﹕ at com.af.ftsm.testing.MainActivity$Task.doInBackground(MainActivity.java:39)
06-15 10:33:33.938  16885-17179/com.af.ftsm.testing W/System.err﹕ at android.os.AsyncTask$2.call(AsyncTask.java:288)
06-15 10:33:33.938  16885-17179/com.af.ftsm.testing W/System.err﹕ at java.util.concurrent.FutureTask.run(FutureTask.java:237)
06-15 10:33:33.938  16885-17179/com.af.ftsm.testing W/System.err﹕ at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
06-15 10:33:33.938  16885-17179/com.af.ftsm.testing W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
06-15 10:33:33.938  16885-17179/com.af.ftsm.testing W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
06-15 10:33:33.938  16885-17179/com.af.ftsm.testing W/System.err﹕ at java.lang.Thread.run(Thread.java:841)

＆＃13;

我在表中添加项目的方法是错误的还是其他方法？谢谢。

Answer 1

根据这些信息，我相信资源R.id.text1不存在，所以findViewById返回null。类型转换为null将抛出NPE。如果没有，请告诉我们Add_Item.java第26行的内容。

PS：您最好在生产级Android应用中避免使用PropertiesCredentials。 CognitoCachingCredentialsProvider是获取AWS凭据的推荐方式。有关详细信息，请参阅Amazon Cognito Identity。

从EditText获取AWS DynamoDB中的表值

1 个答案: