我的代码抛出NullPointerException。
这是我的java代码：
public class DbselectActivity extends Activity
{
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button = (Button) findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener()
{
public void onClick(View view)
{
String result = null;
InputStream is = null;
try{
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://192.168.1.0:81/selectall.php");
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
Log.e("log_tag", "connection success ");
// Toast.makeText(getApplicationContext(), "pass", Toast.LENGTH_SHORT).show();
}
catch(Exception e)
{
Log.e("log_tag", "Error in http connection "+e.toString());
Toast.makeText(getApplicationContext(), "Connection fail", Toast.LENGTH_SHORT).show();
}
//convert response to string
try
{
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null)
{
sb.append(line + "\n");
// Toast.makeText(getApplicationContext(), "Input Reading pass", Toast.LENGTH_SHORT).show();
}
is.close();
result=sb.toString();
}
catch(Exception e)
{
Log.e("log_tag", "Error converting result "+e.toString());
Toast.makeText(getApplicationContext(), " Input reading fail", Toast.LENGTH_SHORT).show();
}
//parse json data
try
{
JSONArray jArray = new JSONArray(result);
String re=jArray.getString(jArray.length()-1);
TableLayout tv=(TableLayout) findViewById(R.id.table);
tv.removeAllViewsInLayout();
int flag=1;
for(int i=-1;i<jArray.length()-1;i++)
{
TableRow tr=new TableRow(DbselectActivity.this);
tr.setLayoutParams(new LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.WRAP_CONTENT));
if(flag==1)
{
TextView b6=new TextView(DbselectActivity.this);
b6.setText("ID");
b6.setTextColor(Color.BLUE);
b6.setTextSize(15);
tr.addView(b6);
TextView b19=new TextView(DbselectActivity.this);
b19.setPadding(10, 0, 0, 0);
b19.setTextSize(15);
b19.setText("Name");
b19.setTextColor(Color.BLUE);
tr.addView(b19);
TextView b29=new TextView(DbselectActivity.this);
b29.setPadding(10, 0, 0, 0);
b29.setText("no");
b29.setTextColor(Color.BLUE);
b29.setTextSize(15);
tr.addView(b29);
tv.addView(tr);
final View vline = new View(DbselectActivity.this);
vline.setLayoutParams(new TableRow.LayoutParams(TableRow.LayoutParams.FILL_PARENT, 2));
vline.setBackgroundColor(Color.BLUE);
tv.addView(vline);
flag=0;
}
else
{
JSONObject json_data = jArray.getJSONObject(i);
Log.i("log_tag","id: "+json_data.getInt("f1")+
", Username: "+json_data.getString("f2")+
", No: "+json_data.getInt("f3"));
TextView b=new TextView(DbselectActivity.this);
String stime=String.valueOf(json_data.getInt("f1"));
b.setText(stime);
b.setTextColor(Color.RED);
b.setTextSize(15);
tr.addView(b);
TextView b1=new TextView(DbselectActivity.this);
b1.setPadding(10, 0, 0, 0);
b1.setTextSize(15);
String stime1=json_data.getString("f2");
b1.setText(stime1);
b1.setTextColor(Color.WHITE);
tr.addView(b1);
TextView b2=new TextView(DbselectActivity.this);
b2.setPadding(10, 0, 0, 0);
String stime2=String.valueOf(json_data.getInt("f3"));
b2.setText(stime2);
b2.setTextColor(Color.RED);
b2.setTextSize(15);
tr.addView(b2);
tv.addView(tr);
final View vline1 = new View(DbselectActivity.this);
vline1.setLayoutParams(new TableRow.LayoutParams(TableRow.LayoutParams.FILL_PARENT, 1));
vline1.setBackgroundColor(Color.WHITE);
tv.addView(vline1);
}
}
}
catch(JSONException e)
{
Log.e("log_tag", "Error parsing data "+e.toString());
Toast.makeText(getApplicationContext(), "JsonArray fail", Toast.LENGTH_SHORT).show();
}
}
});
}
}
我的PHP代码是：
<?php
$con = mysql_connect("localhost","root","");
if (!$con)
{
die('Could not connect: ' . mysql_error());
}
mysql_select_db("ex1", $con);
$i=mysql_query("select * from t1",$con);
$num_rows = mysql_num_rows($i);
$check='';
while($row = mysql_fetch_array($i))
{
$r[]=$row;
$check=$row['f1'];
}
if($check==NULL)
{
$r[$num_rows]="Record is not available";
print(json_encode($r));
}
else
{
$r[$num_rows]="success";
print(json_encode($r));
}
mysql_close($con);
?>
Logcat是：
致命的例外：主要 处理：com.example.dell.dbselect，PID：16779 java.lang.NullPointerException：尝试调用虚方法'int 空对象引用上的java.lang.String.length（）' 在org.json.JSONTokener.nextCleanInternal（JSONTokener.java:116） at org.json.JSONTokener.nextValue（JSONTokener.java:94） 在org.json.JSONArray。（JSONArray.java:92） 在org.json.JSONArray。（JSONArray.java:108） 在 com.example.dell.dbselect.DbselectActivity $ 1.onClick（DbselectActivity.java:81） 在android.view.View.performClick（View.java:5198） 在android.view.View $ PerformClick.run（View.java:21147） 在android.os.Handler.handleCallback（Handler.java:739） 在android.os.Handler.dispatchMessage（Handler.java:95） 在android.os.Looper.loop（Looper.java:148） 在android.app.ActivityThread.main（ActivityThread.java:5417） at java.lang.reflect.Method.invoke（Native Method） 在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:726） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:616)08
我已经尝试了很多，但同样的错误发生了。指导我。
答案 0 :(得分：0)
评论此行，然后尝试
String re=jArray.getString(jArray.length()-1);