我的代码有时会出现空指针异常。奇怪的是,这种情况并不是每次都会发生,我也不知道为什么。帮忙?
package net.obviam.droidz;
public class HomeView extends Activity {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.menu);
Button page1 = (Button) findViewById(R.id.Button01);
page1.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
// Intent i = getIntent();
Intent myIntent = new Intent(view.getContext(), DroidzActivity.class);
startActivityForResult(myIntent, 0);
}
});
}
protected void onDestroy() {
// Log.d(TAG, "Destroying..");
super.onDestroy();
}
@Override
protected void onStop() {
// Log.d(TAG, "Stopping...");
super.onStop();
}
}
logcat 表明问题出在第 19 行,即 setOnClickListener。我不确定它有什么问题。它似乎没有引用任何内容。
Logcat 的内容如下:
02-17 16:52:13.816: E/AndroidRuntime(23756): FATAL EXCEPTION: main
02-17 16:52:13.816: E/AndroidRuntime(23756): java.lang.RuntimeException: Unable to start activity ComponentInfo{net.obviam.droidz/net.obviam.droidz.HomeView}: java.lang.NullPointerException
02-17 16:52:13.816: E/AndroidRuntime(23756): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
02-17 16:52:13.816: E/AndroidRuntime(23756): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
02-17 16:52:13.816: E/AndroidRuntime(23756): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
02-17 16:52:13.816: E/AndroidRuntime(23756): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
02-17 16:52:13.816: E/AndroidRuntime(23756): at android.os.Handler.dispatchMessage(Handler.java:99)
02-17 16:52:13.816: E/AndroidRuntime(23756): at android.os.Looper.loop(Looper.java:130)
02-17 16:52:13.816: E/AndroidRuntime(23756): at android.app.ActivityThread.main(ActivityThread.java:3687)
02-17 16:52:13.816: E/AndroidRuntime(23756): at java.lang.reflect.Method.invokeNative(Native Method)
02-17 16:52:13.816: E/AndroidRuntime(23756): at java.lang.reflect.Method.invoke(Method.java:507)
02-17 16:52:13.816: E/AndroidRuntime(23756): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842)
02-17 16:52:13.816: E/AndroidRuntime(23756): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
02-17 16:52:13.816: E/AndroidRuntime(23756): at dalvik.system.NativeStart.main(Native Method)
02-17 16:52:13.816: E/AndroidRuntime(23756): Caused by: java.lang.NullPointerException
02-17 16:52:13.816: E/AndroidRuntime(23756): at net.obviam.droidz.HomeView.onCreate(HomeView.java:19)
02-17 16:52:13.816: E/AndroidRuntime(23756): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
02-17 16:52:13.816: E/AndroidRuntime(23756): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
02-17 16:52:13.816: E/AndroidRuntime(23756): ... 11 more
这是 list 文件:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="net.obviam.droidz"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk android:minSdkVersion="10" />
<application
android:icon="@drawable/images"
android:label="@string/app_name" android:debuggable="true">
<activity android:name=".HomeView" 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=".DroidzActivity"></activity>
</application>
这是该按钮所在的 xml 文件:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<Button android:text="Start Game!"
android:id="@+id/Button01"
android:layout_width="250dp"
android:textSize="18dp"
android:layout_height="55dp">
</Button>
</LinearLayout>
最佳答案
阅读完提供的堆栈跟踪后,我认为问题是当您启动新 Intent 时,您要传递 Activity 的上下文,而不是 View 的:
Button page1 = (Button) findViewById(R.id.Button01);
page1.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent myIntent = new Intent(getContext(), DroidzActivity.class); // fix View.getContext() to getContext()
startActivity(myIntent); // change to startActivity
}
});
至于为什么这是一个间歇性问题,我不知道。
关于java - setOnClickListener() 的空指针异常,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/9336615/