我尝试通过点击按钮将当前活动从主活动更改为另一个活动，但之后它无法正常工作。当我点击按钮时，它会崩溃应用程序，我不知道为什么会这样做。我还尝试在MainActivity.java上将布局更改为所需的布局，并且模拟器成功加载了活动，因此我认为在单击时调用的方法存在一些问题。
MainActivity.java
package com.example.user.partyminigames;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
/* AppCompatActivity*/
public class MainActivity extends Activity {
private Context context;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/* Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar); */
/* FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
}); */
}
public void onClick(View view) {
Intent intent = new Intent();
switch (view.getId()) {
case R.id.button:
intent.setClass(context, NumberGuessingActivity.class);
startActivity(intent);
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.menu_main, menu);
return true;
}
@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);
}
}
NumberGuessingActivity.java
package com.example.user.partyminigames;
import android.app.Activity;
import android.os.Bundle;
/**
* Created by USER on 26/12/2015.
*/
public class NumberGuessingActivity extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_numberguessing);
}
}
的AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.user.partyminigames" >
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:theme="@style/AppTheme.NoActionBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".NumberGuessingActivity">
<intent-filter>
<action android:name="number.guessing"/>
<category android:name="android.intent.category.DEFAULT"/>
</intent-filter>
</activity>
</application>
</manifest>
content_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/activity_main" tools:context=".MainActivity">
<TextView android:text="@string/testing" android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/textView2" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/asplode"
android:id="@+id/textView"
android:layout_below="@+id/textView2"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:autoText="false"
android:textColor="@color/lose" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/button_numberGuessing"
android:id="@+id/button"
android:layout_marginTop="111dp"
android:layout_below="@+id/textView"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:onClick="onClick" />
</RelativeLayout>
activity_main.xml中
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:fitsSystemWindows="true"
tools:context=".MainActivity">
<android.support.design.widget.AppBarLayout android:layout_height="wrap_content"
android:layout_width="match_parent" android:theme="@style/AppTheme.AppBarOverlay">
<!-- <android.support.v7.widget.Toolbar android:id="@+id/toolbar" -->
<!-- android:layout_width="match_parent" android:layout_height="?attr/actionBarSize" -->
<!-- android:background="?attr/colorPrimary" app:popupTheme="@style/AppTheme.PopupOverlay" /> -->
</android.support.design.widget.AppBarLayout>
<include layout="@layout/content_main" />
<!-- <android.support.design.widget.FloatingActionButton android:id="@+id/fab" -->
<!-- android:layout_width="wrap_content" android:layout_height="wrap_content" -->
<!-- android:layout_gravity="bottom|end" android:layout_margin="@dimen/fab_margin" -->
<!-- android:src="@android:drawable/ic_dialog_email" /> -->
</android.support.design.widget.CoordinatorLayout>
logcat的
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: FATAL EXCEPTION: main
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: Process: com.example.user.partyminigames, PID: 1878
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: java.lang.IllegalStateException: Could not execute method of the activity
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.view.View$1.onClick(View.java:3823)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.view.View.performClick(View.java:4438)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.view.View$PerformClick.run(View.java:18422)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:733)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:95)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.os.Looper.loop(Looper.java:136)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5001)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:515)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: Caused by: java.lang.reflect.InvocationTargetException
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:515)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.view.View$1.onClick(View.java:3818)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.view.View.performClick(View.java:4438)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.view.View$PerformClick.run(View.java:18422)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:733)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:95)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.os.Looper.loop(Looper.java:136)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5001)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:515)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: Caused by: java.lang.NullPointerException
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.content.ComponentName.<init>(ComponentName.java:77)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.content.Intent.setClass(Intent.java:6360)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at com.example.user.partyminigames.MainActivity.onClick(MainActivity.java:39)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:515)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.view.View$1.onClick(View.java:3818)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.view.View.performClick(View.java:4438)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.view.View$PerformClick.run(View.java:18422)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:733)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:95)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.os.Looper.loop(Looper.java:136)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5001)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:515)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
12-27 01:25:49.436 1878-1878/? E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method)
12-27 01:25:49.456 360-404/? E/SoundPool: error loading /system/media/audio/ui/Effect_Tick.ogg
12-27 01:25:49.456 360-404/? E/SoundPool: error loading /system/media/audio/ui/Effect_Tick.ogg
12-27 01:25:49.456 360-404/? E/SoundPool: error loading /system/media/audio/ui/Effect_Tick.ogg
12-27 01:25:49.466 360-404/? E/SoundPool: error loading /system/media/audio/ui/Effect_Tick.ogg
12-27 01:25:49.466 360-404/? E/SoundPool: error loading /system/media/audio/ui/Effect_Tick.ogg
12-27 01:25:49.466 360-404/? E/SoundPool: error loading /system/media/audio/ui/KeypressStandard.ogg
12-27 01:25:49.486 360-404/? E/SoundPool: error loading /system/media/audio/ui/KeypressSpacebar.ogg
12-27 01:25:49.486 360-404/? E/SoundPool: error loading /system/media/audio/ui/KeypressDelete.ogg
12-27 01:25:49.496 360-404/? E/SoundPool: error loading /system/media/audio/ui/KeypressReturn.ogg
12-27 01:25:49.496 360-404/? E/SoundPool: error loading /system/media/audio/ui/KeypressInvalid.ogg
我试图按照本书教我在Android中编码的内容，但我仍然坚持改变活动。希望上面的代码/日志提供足够的信息。
编辑：它是一个空指针异常，但我无法在日志中找到告诉我的位置。感谢您通知我非常常见的空指针异常。
答案 0 :(得分：2)
在content上，未初始化上下文变量。
更改
fmt.Printf("%+v\n", content)
到
MainActivity.java并删除
intent.setClass(context, NumberGuessingActivity.class);
答案 1 :(得分：0)
intent.setClass(this, NumberGuessingActivity.class);
答案 2 :(得分：0)
您有context null，即未在
intent.setClass(context, NumberGuessingActivity.class);
使用
intent.setClass(this, NumberGuessingActivity.class);
答案 3 :(得分：0)
您尚未初始化上下文。所以要么在onCreate中这样做：context = this.getContext（）或者更好的只是在你的onClick（）中替换你的
intent.setClass(context, NumberGuessingActivity.class);
带
intent.setClass(this, NumberGuessingActivity.class);