android在eclipse中的崩溃android SDK

我是android开发的初学者。我的代码有问题。该应用程序完全崩溃。主要是Java错误。android在eclipse中的崩溃android SDK

MainActivity.java：

package hu.cgkni6.uniobuda.testapplication; 

import hu.cgkni6.uniobuda.testapplication.R; 
import android.os.Bundle; 
import android.app.Activity; 
import android.view.Menu; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.Toast; 


public class MainActivity extends Activity { 

    final String username = "diak"; 
    final String pass = "diak"; 
    Button okbutton = (Button) findViewById(R.id.btn_OK); 
    Button cancelbutton = (Button) findViewById(R.id.btn_Cancel); 
    final EditText usrname = (EditText) findViewById(R.id.editText1); 
    final EditText passwd = (EditText) findViewById(R.id.editText2); 





    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     okbutton.setOnClickListener(new View.OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       // TODO Auto-generated method stub 
       if (usrname.getText().toString().equals(username)) 
       { 
        if (passwd.getText().toString().equals(pass)) 
        { 
         String text2 = "Success!"; 
         Toast.makeText(MainActivity.this, text2, Toast.LENGTH_LONG).show(); 

        } 
        else { 
         Toast.makeText(MainActivity.this, "Invalid Password", Toast.LENGTH_LONG).show(); 
        } 
       } 
       else { 
        Toast.makeText(MainActivity.this, "Invalid username", Toast.LENGTH_LONG).show(); 
       } 
      } 
     }); 

     cancelbutton.setOnClickListener(new View.OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       // TODO Auto-generated method stub 
       finish(); 
      } 
     }); 

    } 


    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.main, menu); 
     return true; 
    } 

}

activity_main.xml中：

<LinearLayout android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:orientation="vertical" xmlns:android="http://schemas.android.com/apk/res/android" 
    android:background="#45B7FA" > 

    <TextView 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_marginBottom="15dp" 
     android:layout_marginTop="15dp" 
     android:gravity="center_horizontal" 
     android:textColor="#FFFFFF" 
     android:textSize="30sp" 
     android:text="@string/login_interface" /> 


    <LinearLayout 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:gravity="right" 
     android:orientation="horizontal" > 


      <TextView 
       android:id="@+id/textView1" 
       android:layout_width="100dp" 
       android:layout_height="wrap_content" 
       android:text="@string/username" 
       android:textAppearance="?android:attr/textAppearanceMedium" /> 

      <EditText 
       android:id="@+id/editText1" 
       android:layout_width="match_parent" 
       android:layout_height="wrap_content" 
       android:inputType="textEmailAddress" 
       android:hint="@string/username" > 

       <requestFocus /> 
      </EditText>  
     </LinearLayout> 


    <LinearLayout 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:layout_marginBottom="5dp" 
     android:gravity="right" 
     android:orientation="horizontal" > 


      <TextView 
       android:id="@+id/textView2" 
       android:layout_width="100dp" 
       android:layout_height="wrap_content" 
       android:text="@string/password" 
       android:textAppearance="?android:attr/textAppearanceMedium" /> 

      <EditText 
       android:id="@+id/editText2" 
       android:layout_width="match_parent" 
       android:layout_height="wrap_content" 
       android:inputType="textPassword" 
       android:hint="@string/password" > 

      </EditText>  
     </LinearLayout> 



    <LinearLayout 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:gravity="right" 
     android:orientation="horizontal" > 

     <Button 
      android:id="@+id/btn_OK" 
      android:layout_marginLeft="10dp" 
      android:layout_marginRight="10dp" 
      android:layout_weight="1" 
      android:layout_width="0dp" 
      android:layout_height="45dp" 
      android:background="#FFFFFF" 
      android:textColor="#000000" 
      android:textSize="20sp" 
      android:text="@string/ok" /> 
     <Button 
      android:id="@+id/btn_Cancel" 
      android:layout_marginLeft="10dp" 
      android:layout_marginRight="10dp" 
      android:layout_weight="1" 
      android:layout_width="0dp" 
      android:layout_height="45dp" 
      android:background="#FFFFFF" 
      android:textColor="#000000" 
      android:textSize="20sp" 
      android:text="@string/cancel" /> 
    </LinearLayout> 

    <RelativeLayout 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" > 

     <TableRow 
      android:id="@+id/tableRow1" 
      android:layout_width="fill_parent" 
      android:layout_height="wrap_content" 

      android:layout_alignParentBottom="true" 
      android:layout_marginBottom="3dp" > 

      <Button 
       android:id="@+id/button1" 
       android:layout_width="0dp" 
       android:layout_height="35dp" 
       android:layout_weight="1" 
       android:layout_marginLeft="5dp" 
       android:background="#FFFFFF" 
       android:textColor="#000000" 
       android:text="@string/about_us" 

/> 

      <Button 
       android:id="@+id/button2" 
       android:layout_width="0dp" 
       android:layout_height="35dp" 
       android:layout_weight="1" 
       android:layout_marginLeft="5dp" 
       android:layout_marginRight="5dp" 
       android:background="#FFFFFF" 
       android:textColor="#000000" 
       android:text="@string/contact_us" /> 

      <Button 
       android:id="@+id/button3" 
       android:layout_width="0dp" 
       android:layout_height="35dp" 
       android:layout_weight="1" 
       android:layout_marginRight="5dp" 
       android:background="#FFFFFF" 
       android:textColor="#000000" 
       android:text="@string/help" /> 
     </TableRow> 

    </RelativeLayout> 

</LinearLayout>

目录下载：

10-09 09:18:26.244: E/AndroidRuntime(302): FATAL EXCEPTION: main 
10-09 09:18:26.244: E/AndroidRuntime(302): java.lang.RuntimeException: Unable to instantiate activity  ComponentInfo{hu.cgkni6.uniobuda.testapplication/hu.cgkni6.uniobuda.testapplication.MainActivity}: java.lang.NullPointerException 
10-09 09:18:26.244: E/AndroidRuntime(302): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585) 
10-09 09:18:26.244: E/AndroidRuntime(302): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 
10-09 09:18:26.244: E/AndroidRuntime(302): at android.app.ActivityThread.access$2300(ActivityThread.java:125) 
10-09 09:18:26.244: E/AndroidRuntime(302): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 
10-09 09:18:26.244: E/AndroidRuntime(302): at android.os.Handler.dispatchMessage(Handler.java:99) 
10-09 09:18:26.244: E/AndroidRuntime(302): at android.os.Looper.loop(Looper.java:123) 
10-09 09:18:26.244: E/AndroidRuntime(302): at android.app.ActivityThread.main(ActivityThread.java:4627) 
10-09 09:18:26.244: E/AndroidRuntime(302): at java.lang.reflect.Method.invokeNative(Native Method) 
10-09 09:18:26.244: E/AndroidRuntime(302): at java.lang.reflect.Method.invoke(Method.java:521) 
10-09 09:18:26.244: E/AndroidRuntime(302): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
10-09 09:18:26.244: E/AndroidRuntime(302): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
10-09 09:18:26.244: E/AndroidRuntime(302): at dalvik.system.NativeStart.main(Native Method) 
10-09 09:18:26.244: E/AndroidRuntime(302): Caused by: java.lang.NullPointerException 
10-09 09:18:26.244: E/AndroidRuntime(302): at android.app.Activity.findViewById(Activity.java:1637) 
10-09 09:18:26.244: E/AndroidRuntime(302): at hu.cgkni6.uniobuda.testapplication.MainActivity.<init>(MainActivity.java:17) 
10-09 09:18:26.244: E/AndroidRuntime(302): at java.lang.Class.newInstanceImpl(Native Method) 
10-09 09:18:26.244: E/AndroidRuntime(302): at java.lang.Class.newInstance(Class.java:1429) 
10-09 09:18:26.244: E/AndroidRuntime(302): at android.app.Instrumentation.newActivity(Instrumentation.java:1021) 
10-09 09:18:26.244: E/AndroidRuntime(302): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577) 
10-09 09:18:26.244: E/AndroidRuntime(302): ... 11 more

来源

2013-10-09 András Urfi

Urfi查看我的答案。 – GrIsHu

THX All ... Stupidus是第一个评论者...我给他的分数 –

Atleast赞赏别人的答案也。 – GrIsHu

Button okbutton = (Button) findViewById(R.id.btn_OK); 
Button cancelbutton = (Button) findViewById(R.id.btn_Cancel); 
final EditText usrname = (EditText) findViewById(R.id.editText1); 
final EditText passwd = (EditText) findViewById(R.id.editText2);

把这个放在setContentView（R.layout.activity_main）之后的oncreate方法中; ，你应该很好。你不能从那个位置执行它:)

来源

2013-10-09 09:37:08 Stupidus

THX ...这是工作...你是第一个:) –

你应该在设置onCreate()方法中的布局之后初始化你的视图。由于您在设置布局之前尝试访问视图，因此应用程序无法找到视图的ID，因此您会看到该错误。

如下更改代码：

@Override 
    protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    Button okbutton = (Button) findViewById(R.id.btn_OK); 
    Button cancelbutton = (Button) findViewById(R.id.btn_Cancel); 
    final EditText usrname = (EditText) findViewById(R.id.editText1); 
    final EditText passwd = (EditText) findViewById(R.id.editText2); 
    }

来源

2013-10-09 09:39:14 GrIsHu

你试图找到意见之前，你的布局设置。移动

Button okbutton = (Button) findViewById(R.id.btn_OK); 
Button cancelbutton = (Button) findViewById(R.id.btn_Cancel); 
final EditText usrname = (EditText) findViewById(R.id.editText1); 
final EditText passwd = (EditText) findViewById(R.id.editText2);

到您的onCreate方法。在您拨打setContentView之后。

来源

2013-10-09 09:39:54 ssantos

首先，你应该学习Android的生命周期你会发现所有的按钮和编辑文本在onCreate方法

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    Button okbutton = (Button) findViewById(R.id.btn_OK); 
      Button cancelbutton = (Button) findViewById(R.id.btn_Cancel); 
      final EditText usrname = (EditText) findViewById(R.id.editText1); 
      final EditText passwd = (EditText) findViewById(R.id.editText2); 
}

来源

2013-10-09 09:53:21 parmitKR

初始化你Button和EditText的onCreate method外面这样

Button okbutton; 
Button cancelbutton; 
EditText usrname; 
EditText passwd;

然后插入这个

okbutton = (Button) findViewById(R.id.btn_OK); 
cancelbutton = (Button) findViewById(R.id.btn_Cancel); 
EditText usrname = (EditText) findViewById(R.id.editText1); 
EditText passwd = (EditText) findViewById(R.id.editText2);

您的onCreate方法内setContentView(R.layout.activity_main);

希望它有帮助。

来源

2013-10-09 09:58:20 RussVirtuoso

android在eclipse中的崩溃android SDK

回答

相关问题