Question

我想知道是否有人可以帮助我。我有一个带有9个按钮的活动，当点击它们改变另一个按钮的颜色时，9个按钮中的每个按钮都会使用以下颜色将按钮的颜色改为不同的颜色：

currentcolour.setBackgroundColor(Color.rgb(0, 255, 0));

用于自定义颜色，或者：

currentcolour.setBackgroundColor(Color.RED);

表示默认颜色

当我在平板电脑上运行应用程序并单击该按钮时，它会抛出空指针异常：

07-09 10:26:21.492: D/AndroidRuntime(8157): Shutting down VM
07-09 10:26:21.492: W/dalvikvm(8157): threadid=1: thread exiting with uncaught exception   (group=0x41986930)
07-09 10:26:21.507: E/AndroidRuntime(8157): FATAL EXCEPTION: main
07-09 10:26:21.507: E/AndroidRuntime(8157): java.lang.NullPointerException
07-09 10:26:21.507: E/AndroidRuntime(8157):     at sjtech.rompa.wifi.Wifi$1.onClick(Wifi.java:54)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at android.view.View.performClick(View.java:4452)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at android.widget.Button.performClick  (Button.java:148)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at android.view.View$PerformClick.run  (View.java:18428)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at android.os.Handler.handleCallback(Handler.java:725)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at android.os.Handler.dispatchMessage(Handler.java:92)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at android.os.Looper.loop(Looper.java:176)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at android.app.ActivityThread.main(ActivityThread.java:5365)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at java.lang.reflect.Method.invokeNative(Native Method)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at java.lang.reflect.Method.invoke(Method.java:511)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
07-09 10:26:21.507: E/AndroidRuntime(8157):     at dalvik.system.NativeStart.main(Native Method)
07-09 10:26:21.539: D/dalvikvm(8157): GC_CONCURRENT freed 668K, 31% free 8844K/12804K, paused    1ms+4ms, total 33ms

这是.java

package sjtech.rompa.wifi;

import com.javacodegeeks.android.bluetoothtest.R;

import android.os.Bundle;
import android.app.Activity;
import android.bluetooth.BluetoothDevice;
import android.content.Intent;
import android.graphics.Color;
import android.view.View;
import android.util.Log;
import android.view.Menu;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;


   //called when the activity is first created
public class Wifi extends Activity {


private Button currentcolour;
private Button redbtn; 
private Button grnbtn;
private Button bluebtn; 
private Button yellowbtn;
private Button orangebtn; 
private Button purplebtn;
private Button pinkbtn; 
private Button whitebtn;
private Button resetbtn;
private Button blueleftarrow; 

//Button wifi_screen changes between screens.
@Override   
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.wifi);




            //****RED BUTTON****
           // Get a reference to the button
    redbtn = (Button) findViewById(R.id.redbtn);  
         // Set the click listener to run the code.
    redbtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

                 // red button's click event
    Toast.makeText(getBaseContext(), "RED " ,   Toast.LENGTH_SHORT ).show();
          currentcolour.setBackgroundColor(Color.RED);


            }   
        });



            //****GREEN BUTTON****
           // Get a reference to the button
                grnbtn = (Button)findViewById(R.id.grnbtn);
         // Set the click listener to run the code.
                grnbtn.setOnClickListener(new OnClickListener() {
                @Override
                public void onClick(View v) {
           // green button's click event
    Toast.makeText(getBaseContext(), "GREEN " , Toast.LENGTH_SHORT ).show();
    currentcolour.setBackgroundColor(Color.rgb(0, 255, 0));

                }
            });


                //****BLUE BUTTON****
               // Get a reference to the button
            bluebtn = (Button)findViewById(R.id.bluebtn);
             // Set the click listener to run the code.
            bluebtn.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                  // blue button's click event
                          Toast.makeText(getBaseContext(), "BLUE " , Toast.LENGTH_SHORT ).show();
            currentcolour.setBackgroundColor(Color.BLUE);
            }
        });


            //****YELLOW BUTTON****
           // Get a reference to the button
        yellowbtn = (Button)findViewById(R.id.yellowbtn);
         // Set the click listener to run the code.
        yellowbtn.setOnClickListener(new OnClickListener() {
            @Override
        public void onClick(View v) {
             // yellow button's click event
    Toast.makeText(getBaseContext(), "YELLOW" , Toast.LENGTH_SHORT ).show();
        currentcolour.setBackgroundColor(Color.YELLOW);
        }
        });



    //****ORANGE BUTTON****
        // Get a reference to the button
    orangebtn = (Button)findViewById(R.id.orangebtn);

       // Set the click listener to run the code.
    orangebtn.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
     // orange button's click event
    Toast.makeText(getBaseContext(), "ORANGE" , Toast.LENGTH_SHORT ).show();
    currentcolour.setBackgroundColor(Color.rgb(255, 100, 0));

        }
    });


    //****PURPLE BUTTON****
     // Get a reference to the button
    purplebtn = (Button)findViewById(R.id.purplebtn);

     // Set the click listener to run the code.
    purplebtn.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {

     // purple button's click event
                 Toast.makeText(getBaseContext(), "PURPLE" , Toast.LENGTH_SHORT ).show();
           currentcolour.setBackgroundColor(Color.rgb(128, 0, 128));
}
});



                                         //****PINK BUTTON****
        // Get a reference to the button
     pinkbtn = (Button)findViewById(R.id.pinkbtn);

     // Set the click listener to run the code.
              pinkbtn.setOnClickListener(new OnClickListener() {
                                          @Override
      public void onClick(View v) {

            // pink button's click event
       Toast.makeText(getBaseContext(), "PINK" , Toast.LENGTH_SHORT ).show();
       currentcolour.setBackgroundColor(Color.rgb(255, 20, 147));
                                    }
});



                                      //****WHITE BUTTON****
 // Get a reference to the button
    whitebtn = (Button)findViewById(R.id.whitebtn);

        //Set the click listener to run the code.
    whitebtn.setOnClickListener(new OnClickListener() {
                                            @Override
           public void onClick(View v) {

        //white button's click event
    Toast.makeText(getBaseContext(), "WHITE" , Toast.LENGTH_SHORT ).show();
    currentcolour.setBackgroundColor(Color.WHITE);
                                        }
                                    });

                                        //****GRAY BUTTON****
// Get a reference to the button
   resetbtn = (Button)findViewById(R.id.resetbtn);
                                     // Set the click listener to run the code.
    resetbtn.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {

 // gray button's click event
    Toast.makeText(getBaseContext(), "RESET" , Toast.LENGTH_SHORT ).show();
    currentcolour.setBackgroundColor(Color.TRANSPARENT);
                                        }
                                        });


       //****blueleftarrow BUTTON****
      //changes from wifi to bluetooth page.      
     // Get a reference to the button
  blueleftarrow = (Button)findViewById(R.id.blueleftarrow);

// Set the click listener to run the code.
   blueleftarrow.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View v) {

 //blueleftarrow's click event
   Intent intent = new Intent(v.getContext(), Bluetoothsetup.class);
   startActivity(intent);   


        }
    });  

}
}

和.xml

<AbsoluteLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/clouds"
android:focusable="false"
android:focusableInTouchMode="false"
android:layoutMode="clipBounds"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:visibility="visible"
tools:context=".Wifi" >


<ImageView
    android:id="@+id/imageView1"
    android:layout_width="193dp"
    android:layout_height="wrap_content"
    android:layout_x="0dp"
    android:layout_y="0dp"
    android:src="@drawable/rompalogo" />

<Button
    android:id="@+id/orangebtn"
    android:layout_width="130dp"
    android:layout_height="130dp"
    android:layout_x="223dp"
    android:layout_y="750dp"
    android:background="@drawable/orangecircle2" />

<Button
    android:id="@+id/whitebtn"
    style="@android:style/Animation"
    android:layout_width="130dp"
    android:layout_height="130dp"
    android:layout_x="63dp"
    android:layout_y="673dp"
    android:background="@drawable/whitecircle2" />

<Button
    android:id="@+id/pinkbtn"
    android:layout_width="130dp"
    android:layout_height="130dp"
    android:layout_x="395dp"
    android:layout_y="685dp"
    android:background="@drawable/pinkcircle2" />

<Button
    android:id="@+id/resetbtn"
    android:layout_width="130dp"
    android:layout_height="130dp"
    android:layout_x="223dp"
    android:layout_y="497dp"
    android:background="@drawable/greycircle2" />

<Button
    android:id="@+id/purplebtn"
    android:layout_width="130dp"
    android:layout_height="130dp"
    android:layout_x="432dp"
    android:layout_y="493dp"
    android:background="@drawable/purplecircle2" />

<Button
    android:id="@+id/yellowbtn"
    android:layout_width="130dp"
    android:layout_height="130dp"
    android:layout_x="25dp"
    android:layout_y="499dp"
    android:background="@drawable/yellowcircle2" />

<Button
    android:id="@+id/bluebtn"
    android:layout_width="130dp"
    android:layout_height="130dp"
    android:layout_x="387dp"
    android:layout_y="332dp"
    android:background="@drawable/bluecircle2" />

<Button
    android:id="@+id/redbtn"
    android:layout_width="130dp"
    android:layout_height="130dp"
    android:layout_x="223dp"
    android:layout_y="259dp"
    android:background="@drawable/redcircle2" />

<Button
    android:id="@+id/grnbtn"
    android:layout_width="130dp"
    android:layout_height="130dp"
    android:layout_x="62dp"
    android:layout_y="340dp"
    android:background="@drawable/greencircle2" />

<Button
    android:id="@+id/blueleftarrow"
    android:layout_width="80dp"
    android:layout_height="80dp"
    android:layout_x="6dp"
    android:layout_y="53dp"
    android:background="@drawable/blueleftarrow" />

<Button
    android:id="@+id/currentcolour"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_x="438dp"
    android:layout_y="66dp"
    android:text="" />

</AbsoluteLayout>

提前致谢！

Answer 1

您尚未初始化Button currentcolour;并且您在点击监听器中使用它作为（即） currentcolour.setBackgroundColor(Color.RED);导致NullPointerException因为currentcolour 1}}是null。

currentcolour= (Button) findViewById(R.id.currentcolour);//Initialize first

<子> Want to Know More about NullPointerException?

Answer 2

在您的代码中，您使用了currentcolor，它尚未初始化并且您正在尝试使用它。这就是你得到空指针异常的原因。

Answer 3

这样做

//Initialize
currentcolour= (Button) findViewById(R.id.currentcolour);

//Set Colour
currentcolour.setBackgroundColor(Color.RED);

Answer 4

在您使用

的第54行的代码中

currentcolour.setBackgroundColor(Color.RED);

没有初始化currentcolor button对象首先初始化它使用它。如果您使用curentcolor而不启动它，您将获得NullPointerException

空指针异常

4 个答案: