android- NullPointerException在TextView的setText（）

Question

我很新的android和我試圖發送一個請求到服務器，並通過api從它獲取數據。但我有一個NullPointerException錯誤，當我點擊loginbtn那裏在沒有發生，除非NullPointerException異常錯誤

這是我的代碼

import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.Window; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 

import java.io.BufferedReader; 
import java.io.InputStreamReader; 
import java.io.OutputStreamWriter; 
import java.io.UnsupportedEncodingException; 
import java.net.URL; 
import java.net.URLConnection; 
import java.net.URLEncoder; 

public class DisplayLoginActivity extends AppCompatActivity { 

    TextView errorText; 
    EditText email, password; 
String Email, Password; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    this.requestWindowFeature(Window.FEATURE_NO_TITLE); 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_display_login); 


    email  = (EditText)findViewById(R.id.emailText); 
    password  = (EditText)findViewById(R.id.passwordText); 


    Button login_btn=(Button)findViewById(R.id.loginbtn); 

    login_btn.setOnClickListener(new Button.OnClickListener(){ 

     public void onClick(View v) 
     { 
      try{ 

       // CALL GetText method to make post method call 
       loginAction(); 
      } 
      catch(Exception ex) 
      { 
       errorText.setText("url! "); 
      } 
     } 
    }); 


} 

// Create GetText Metod 
public void loginAction() throws UnsupportedEncodingException 
{ 
    // Get user defined values 

    Email = email.getText().toString(); 
    Password = password.getText().toString(); 

    // Create data variable for sent values to server 

    String data = URLEncoder.encode("email", "UTF-8") 
      + "=" + URLEncoder.encode(Email, "UTF-8"); 

    data += "&" + URLEncoder.encode("password", "UTF-8") 
      + "=" + URLEncoder.encode(Password, "UTF-8"); 

    String text = ""; 
    BufferedReader reader=null; 

    // Send data 
    try 
    { 

     // Defined URL where to send data 
     URL url = new URL("http://media-clouds.net/pharms/apilogin"); 

     // Send POST data request 

     URLConnection conn = url.openConnection(); 
     conn.setDoOutput(true); 
     OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream()); 
     wr.write(data); 
     wr.flush(); 

     // Get the server response 

     reader = new BufferedReader(new InputStreamReader(conn.getInputStream())); 
     StringBuilder sb = new StringBuilder(); 
     String line = null; 

     // Read Server Response 
     while((line = reader.readLine()) != null) 
     { 
      // Append server response in string 
      sb.append(line + "\n"); 
     } 


     text = sb.toString(); 
    } 
    catch(Exception ex) 
    { 
     errorText.setText("234" ); 
    } 
    finally 
    { 
     try 
     { 

      reader.close(); 
     } 

     catch(Exception ex) { 
      errorText.setText("234" ); 
     } 
    } 

    // Show response on activity 
    errorText.setText(text ); 

} 



@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 


      return true; 
     } 

     return super.onOptionsItemSelected(item); 
    } 
} 

Answer 1

您還沒有膨脹ERRORTEXT TextView像你有誇大電子郵件，密碼EditText。請誇大它。

嘗試onCreate()添加此：

errorText = (TextView)findViewById(R.id.your_error_textid); 

我希望它能幫助！