我在使用OnClickListener的多个作业时遇到问题。如果我使用同一个监听器的3个不同的按钮，我的程序运行顺利，但当我使用四个我的应用程序强制关闭。我甚至创建了自己的OnClickListener并将其分配给我的按钮，但仍然强行关闭。
myMainScreen
package com.example.wifisurveillance;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.content.ComponentName;
import android.content.Intent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.net.NetworkInfo;
import android.net.ConnectivityManager;
import android.content.Context;
import android.util.Log;
import android.net.Uri;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.database.Cursor;
import android.provider.MediaStore;
public class myMainScreen extends Activity implements OnClickListener{
boolean isConnected;
private boolean checkWifi() {
ConnectivityManager connManager =
(ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo mWifi = connManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
boolean isConnected = mWifi.isConnected();
return isConnected;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button buttonA = (Button) findViewById(R.id.button1);
Button buttonB = (Button) findViewById(R.id.button2);
Button buttonD = (Button) findViewById(R.id.button4);
Button buttonF = (Button) findViewById(R.id.button6);
buttonA.setOnClickListener(this);
buttonB.setOnClickListener(this);
buttonD.setOnClickListener(this);
buttonF.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId())
{
case R.id.button1:
isConnected = checkWifi();
Log.d("mylog", "Wifi State =" + isConnected);
if (isConnected) {
Intent intent = new Intent(myMainScreen.this, WifiPage.class);
startActivity(intent);
}
else
{
openWifiSettings();
}
break;
case R.id.button2:
Intent i = new Intent(Intent.ACTION_PICK,android.provider.MediaStore.Images.Media.INTERNAL_CONTENT_URI);
final int ACTIVITY_SELECT_IMAGE = 1234;
startActivityForResult(i, ACTIVITY_SELECT_IMAGE);
break;
case R.id.button4:
Intent intent = new Intent(myMainScreen.this, Sensor_log.class);
startActivity(intent);
break;
case R.id.button6:
finish();
System.exit(0);
break;
}
}
@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;
}
public void openWifiSettings(){
final Intent intent = new Intent(Intent.ACTION_MAIN, null);
intent.addCategory(Intent.CATEGORY_DEFAULT);
final ComponentName cn = new ComponentName("com.android.settings", "com.android.settings.wifi.WifiSettings");
intent.setComponent(cn);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity( intent);
}
protected void onActivityResult(int requestCode, int resultCode, Intent data)
{
super.onActivityResult(requestCode, resultCode, data);
switch(requestCode) {
case 1234:
if(resultCode == RESULT_OK){
Uri selectedImage = data.getData();
String[] filePathColumn = {MediaStore.Images.Media.DATA};
Cursor cursor = getContentResolver().query(selectedImage, filePathColumn, null, null, null);
cursor.moveToFirst();
int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
String filePath = cursor.getString(columnIndex);
cursor.close();
Bitmap yourSelectedImage = BitmapFactory.decodeFile(filePath);
/* Now you have choosen image in Bitmap format in object "yourSelectedImage". You can use it in way you want! */
}
}
};
}
的Manifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.wifisurveillance"
android:versionCode="1"
android:versionName="1.0" >
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-sdk
android:minSdkVersion="15"
android:targetSdkVersion="18" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".WifiPage"
android:label="@string/app_name" >
<intent-filter>
<action android:name="com.example.SURVEILLANCEPAGE" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".myMainScreen"
android:label="@string/app_name" >
<intent-filter>
<action android:name="com.example.CLEARSCREEN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".Sensor_log"
android:label="@string/app_name" >
<intent-filter>
<action android:name="com.example.SENSORPAGE" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
Logcat
12-26 18:03:42.040: E/Trace(24982): error opening trace file: No such file or directory (2)
12-26 18:03:42.280: D/dalvikvm(24982): GC_FOR_ALLOC freed 70K, 8% free 9384K/10115K, paused 31ms, total 31ms
12-26 18:03:42.290: I/dalvikvm-heap(24982): Grow heap (frag case) to 10.183MB for 466576-byte allocation
12-26 18:03:42.330: D/dalvikvm(24982): GC_CONCURRENT freed 1K, 8% free 9839K/10631K, paused 14ms+2ms, total 39ms
12-26 18:03:42.330: D/dalvikvm(24982): WAIT_FOR_CONCURRENT_GC blocked 15ms
12-26 18:03:42.350: D/dalvikvm(24982): GC_FOR_ALLOC freed 0K, 8% free 9839K/10631K, paused 23ms, total 23ms
12-26 18:03:42.350: I/dalvikvm-heap(24982): Grow heap (frag case) to 11.183MB for 1049776-byte allocation
12-26 18:03:42.400: D/dalvikvm(24982): GC_CONCURRENT freed 0K, 8% free 10864K/11719K, paused 18ms+3ms, total 47ms
12-26 18:03:42.400: D/dalvikvm(24982): WAIT_FOR_CONCURRENT_GC blocked 19ms
12-26 18:03:42.420: D/InputTransport(24982): Input channel constructed: name='421455b8 com.example.wifisurveillance/com.example.wifisurveillance.MainActivity (client)', fd=41
12-26 18:03:42.550: D/libEGL(24982): loaded /system/lib/egl/libEGL_mali.so
12-26 18:03:42.560: D/libEGL(24982): loaded /system/lib/egl/libGLESv1_CM_mali.so
12-26 18:03:42.570: D/libEGL(24982): loaded /system/lib/egl/libGLESv2_mali.so
12-26 18:03:42.600: D/OpenGLRenderer(24982): Enabling debug mode 0
12-26 18:03:47.545: D/dalvikvm(24982): GC_FOR_ALLOC freed 471K, 11% free 10474K/11719K, paused 17ms, total 17ms
12-26 18:03:47.545: I/dalvikvm-heap(24982): Grow heap (frag case) to 11.388MB for 614416-byte allocation
12-26 18:03:47.575: D/dalvikvm(24982): GC_CONCURRENT freed 2K, 11% free 11072K/12359K, paused 13ms+1ms, total 36ms
12-26 18:03:47.575: D/dalvikvm(24982): WAIT_FOR_CONCURRENT_GC blocked 13ms
12-26 18:03:47.605: D/dalvikvm(24982): GC_FOR_ALLOC freed 0K, 11% free 11072K/12359K, paused 20ms, total 20ms
12-26 18:03:47.605: I/dalvikvm-heap(24982): Grow heap (frag case) to 12.705MB for 1382416-byte allocation
12-26 18:03:47.645: D/dalvikvm(24982): GC_CONCURRENT freed 0K, 10% free 12422K/13767K, paused 15ms+2ms, total 37ms
12-26 18:03:47.645: D/dalvikvm(24982): WAIT_FOR_CONCURRENT_GC blocked 5ms
12-26 18:03:47.675: D/dalvikvm(24982): GC_FOR_ALLOC freed 600K, 15% free 11829K/13767K, paused 17ms, total 17ms
12-26 18:03:47.685: I/dalvikvm-heap(24982): Grow heap (frag case) to 13.125MB for 1048592-byte allocation
12-26 18:03:47.735: D/dalvikvm(24982): GC_CONCURRENT freed <1K, 14% free 12853K/14855K, paused 30ms+2ms, total 57ms
12-26 18:03:47.795: D/dalvikvm(24982): GC_FOR_ALLOC freed 0K, 14% free 12853K/14855K, paused 23ms, total 23ms
12-26 18:03:47.815: I/dalvikvm-heap(24982): Grow heap (frag case) to 15.375MB for 2359312-byte allocation
12-26 18:03:47.866: D/dalvikvm(24982): GC_CONCURRENT freed 0K, 12% free 15157K/17223K, paused 12ms+2ms, total 48ms
12-26 18:03:47.866: D/dalvikvm(24982): WAIT_FOR_CONCURRENT_GC blocked 4ms
12-26 18:03:47.886: D/dalvikvm(24982): GC_FOR_ALLOC freed 1024K, 18% free 14139K/17223K, paused 19ms, total 19ms
12-26 18:03:47.926: D/dalvikvm(24982): GC_FOR_ALLOC freed <1K, 13% free 15115K/17223K, paused 17ms, total 17ms
12-26 18:03:47.946: I/dalvikvm-heap(24982): Grow heap (frag case) to 17.481MB for 2250016-byte allocation
12-26 18:03:47.976: D/dalvikvm(24982): GC_CONCURRENT freed 0K, 12% free 17312K/19463K, paused 13ms+2ms, total 29ms
12-26 18:03:48.076: D/dalvikvm(24982): GC_FOR_ALLOC freed 1232K, 14% free 16922K/19463K, paused 27ms, total 27ms
12-26 18:03:48.076: I/dalvikvm-heap(24982): Grow heap (frag case) to 18.099MB for 1048592-byte allocation
12-26 18:03:48.186: D/dalvikvm(24982): GC_FOR_ALLOC freed <1K, 13% free 17946K/20551K, paused 41ms, total 41ms
12-26 18:03:48.226: D/dalvikvm(24982): GC_FOR_ALLOC freed 0K, 13% free 17946K/20551K, paused 43ms, total 43ms
12-26 18:03:48.256: I/dalvikvm-heap(24982): Grow heap (frag case) to 20.349MB for 2359312-byte allocation
12-26 18:03:48.336: D/dalvikvm(24982): GC_CONCURRENT freed 0K, 12% free 20250K/22919K, paused 30ms+13ms, total 88ms
12-26 18:03:48.336: D/dalvikvm(24982): WAIT_FOR_CONCURRENT_GC blocked 32ms
12-26 18:03:48.416: D/dalvikvm(24982): GC_FOR_ALLOC freed 1024K, 17% free 19231K/22919K, paused 59ms, total 65ms
12-26 18:03:48.426: I/dalvikvm-heap(24982): Grow heap (frag case) to 20.730MB for 1442416-byte allocation
12-26 18:03:48.536: D/dalvikvm(24982): GC_FOR_ALLOC freed <1K, 16% free 20640K/24391K, paused 40ms, total 40ms
12-26 18:03:48.626: D/dalvikvm(24982): GC_FOR_ALLOC freed 0K, 16% free 20640K/24391K, paused 66ms, total 66ms
12-26 18:03:48.656: I/dalvikvm-heap(24982): Grow heap (frag case) to 23.827MB for 3247216-byte allocation
12-26 18:03:48.746: D/dalvikvm(24982): GC_CONCURRENT freed 0K, 14% free 23811K/27591K, paused 13ms+3ms, total 93ms
12-26 18:03:48.786: D/AndroidRuntime(24982): Shutting down VM
12-26 18:03:48.786: W/dalvikvm(24982): threadid=1: thread exiting with uncaught exception (group=0x4116b2a0)
12-26 18:03:48.806: E/AndroidRuntime(24982): FATAL EXCEPTION: main
12-26 18:03:48.806: E/AndroidRuntime(24982): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.wifisurveillance/com.example.wifisurveillance.myMainScreen}: java.lang.NullPointerException
12-26 18:03:48.806: E/AndroidRuntime(24982): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2081)
12-26 18:03:48.806: E/AndroidRuntime(24982): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2106)
12-26 18:03:48.806: E/AndroidRuntime(24982): at android.app.ActivityThread.access$700(ActivityThread.java:134)
12-26 18:03:48.806: E/AndroidRuntime(24982): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1217)
12-26 18:03:48.806: E/AndroidRuntime(24982): at android.os.Handler.dispatchMessage(Handler.java:99)
12-26 18:03:48.806: E/AndroidRuntime(24982): at android.os.Looper.loop(Looper.java:137)
12-26 18:03:48.806: E/AndroidRuntime(24982): at android.app.ActivityThread.main(ActivityThread.java:4856)
12-26 18:03:48.806: E/AndroidRuntime(24982): at java.lang.reflect.Method.invokeNative(Native Method)
12-26 18:03:48.806: E/AndroidRuntime(24982): at java.lang.reflect.Method.invoke(Method.java:511)
12-26 18:03:48.806: E/AndroidRuntime(24982): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
12-26 18:03:48.806: E/AndroidRuntime(24982): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
12-26 18:03:48.806: E/AndroidRuntime(24982): at dalvik.system.NativeStart.main(Native Method)
12-26 18:03:48.806: E/AndroidRuntime(24982): Caused by: java.lang.NullPointerException
12-26 18:03:48.806: E/AndroidRuntime(24982): at com.example.wifisurveillance.myMainScreen.onCreate(myMainScreen.java:45)
12-26 18:03:48.806: E/AndroidRuntime(24982): at android.app.Activity.performCreate(Activity.java:5047)
12-26 18:03:48.806: E/AndroidRuntime(24982): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
12-26 18:03:48.806: E/AndroidRuntime(24982): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2045)
12-26 18:03:48.806: E/AndroidRuntime(24982): ... 11 more
12-26 18:04:06.005: I/Process(24982): Sending signal. PID: 24982 SIG: 9
Xml代码
<RelativeLayout 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/back"
android:gravity="start"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="10dp"
tools:context=".MainActivity" >
<ImageView
android:id="@+id/imageView1"
android:layout_width="60dp"
android:layout_height="60dp"
android:layout_alignLeft="@+id/button1"
android:layout_alignParentTop="true"
android:src="@drawable/ic_launcher" />
<Button
android:id="@+id/button2"
android:layout_width="425dp"
android:layout_height="60dp"
android:layout_alignLeft="@+id/button1"
android:layout_alignRight="@+id/button1"
android:layout_below="@+id/imageView1"
android:background="?android:selectableItemBackground"
android:layout_marginTop="17dp"
android:text="@string/B2"
android:textColor="@android:color/white"
android:textSize="24sp"
android:gravity="center"
/>
<ImageView
android:id="@+id/imageView2"
android:layout_width="60dp"
android:layout_height="60dp"
android:layout_alignLeft="@+id/button2"
android:layout_alignTop="@+id/button2"
android:src="@drawable/gallery" />
<Button
android:id="@+id/button3"
android:layout_width="425dp"
android:layout_height="60dp"
android:layout_alignLeft="@+id/button2"
android:layout_alignRight="@+id/button2"
android:layout_below="@+id/button2"
android:layout_marginTop="17dp"
android:text="@string/B3"
android:textColor="@android:color/white"
android:textSize="23sp"
android:background="?android:selectableItemBackground"
android:gravity="center|right"/>
<ImageView
android:id="@+id/imageView3"
android:layout_width="60dp"
android:layout_height="60dp"
android:layout_alignLeft="@+id/button3"
android:layout_alignTop="@+id/button3"
android:src="@drawable/sensor" />
<Button
android:id="@+id/Button04"
android:layout_width="425dp"
android:layout_height="60dp"
android:layout_alignLeft="@+id/button3"
android:layout_below="@+id/button3"
android:background="?android:selectableItemBackground"
android:gravity="center"
android:text="@string/B4"
android:textColor="@android:color/white"
android:textSize="24sp"
android:layout_marginTop="17dp"/>
<ImageView
android:id="@+id/imageView4"
android:layout_width="60dp"
android:layout_height="60dp"
android:layout_alignLeft="@+id/Button04"
android:layout_alignTop="@+id/Button04"
android:src="@drawable/log" />
<Button
android:id="@+id/button5"
android:layout_width="425dp"
android:layout_height="60dp"
android:layout_alignLeft="@+id/Button04"
android:layout_alignRight="@+id/Button04"
android:layout_below="@+id/Button04"
android:text="@string/B5"
android:textColor="@android:color/white"
android:textSize="24sp"
android:layout_marginTop="17dp"
android:background="?android:selectableItemBackground"/>
<ImageView
android:id="@+id/imageView5"
android:layout_width="60dp"
android:layout_height="60dp"
android:layout_alignLeft="@+id/button5"
android:layout_alignTop="@+id/button5"
android:src="@drawable/help" />
<Button
android:id="@+id/button6"
android:layout_width="425dp"
android:layout_height="60dp"
android:layout_alignLeft="@+id/button4"
android:layout_alignRight="@+id/button4"
android:layout_below="@+id/button5"
android:layout_marginTop="17dp"
android:text="@string/B6"
android:textColor="@android:color/white"
android:textSize="24sp"
android:background="?android:selectableItemBackground"/>
<ImageView
android:id="@+id/imageView6"
android:layout_width="60dp"
android:layout_height="60dp"
android:layout_alignLeft="@+id/button6"
android:layout_alignTop="@+id/button6"
android:src="@drawable/exit" />
<Button
android:id="@+id/button1"
android:layout_width="425dp"
android:layout_height="60dp"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:background="?android:selectableItemBackground"
android:gravity="center|right"
android:text="@string/B1"
android:textColor="@android:color/white"
android:textSize="24sp" />
</RelativeLayout>
答案 0 :(得分：0)
布局中没有button4，因此findViewById()返回null。在setOnClickListener()上调用null会导致异常。
button4标识符本身是由布局@+id/button4引用引入的。