Android编程：控制器类中的按钮监听器异常

Question

我有一个活动和一个按钮，通过单击我想要打开的另一个活动。我想在我的控制器类执行按钮点击事件，所以我用

里面我MainActivity.java

MainController mainController = new MainController(btn_secondpage); 
btn_secondpage.setOnClickListener(mainController); 

和MainController类我用这些方法 -

内部MainController类别..

public MainController(Button btn_secondpage) { 

    this.btn_secondpage=btn_secondpage; 

    } 

@Override 
public void onClick(View v) { 
    Intent intent = new Intent("com.testandroidproject.view.SecondActivity"); 
    startActivity(intent); 

} 

但每当我点击按钮，一个对话框打开，并显示我的应用程序已停止工作...... 我使用日食mars2 我已经提供了所有我的班，XML的，的manifest.xml

1. activity_main.xml中

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:id="@+id/layout_id" 
    style="@style/AppTheme" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:focusable="false" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    tools:context="com.testandroidproject.view.MainActivity" > 

    <Button 
     android:id="@+id/btn_secondpage" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_centerHorizontal="true" 
     android:layout_centerVertical="true" 
     android:text="Second page" /> 

</RelativeLayout> 

activity_second.xml

<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:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    tools:context="com.testandroidproject.view.SecondActivity" > 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_centerHorizontal="true" 
     android:layout_centerVertical="true" 
     android:text="Welcome to second page" /> 

</RelativeLayout> 

MainActivity.java

package com.testandroidproject.view; 

import com.example.testandroidproject.R; 
import com.testandroidproject.controller.MainController; 

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 

public class MainActivity extends Activity { 

    public Button btn_secondpage; 
    public static final String TAG = "abcd"; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     Log.i(TAG, "inside oncreate");    // printing (1st) 
     btn_secondpage = (Button)findViewById(R.id.btn_secondpage); 
     MainController mainController = new MainController(btn_secondpage); 
     btn_secondpage.setOnClickListener(mainController); 

     //  onButtonClick(); // this is working properly 
    } 

    ////////////// this method is working properly....... 
    public void onButtonClick(){ 
     btn_secondpage = (Button)findViewById(R.id.btn_secondpage); 
     btn_secondpage.setOnClickListener(
       new OnClickListener() { 

        @Override 
        public void onClick(View v) { 
         Intent intent = new Intent("com.testandroidproject.view.SecondActivity"); 
         startActivity(intent); 

        } 
       }); 
    } 

    @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; 
    } 

    @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(); 
     if (id == R.id.action_settings) { 
      return true; 
     } 
     return super.onOptionsItemSelected(item); 
    } 
} 

SecondActivity.java

package com.testandroidproject.view; 

import com.example.testandroidproject.R; 

import android.app.Activity; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 

public class SecondActivity extends Activity { 

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

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

MainController.java

package com.testandroidproject.controller; 

import android.app.Activity; 
import android.content.Intent; 
import android.util.Log; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 

public class MainController extends Activity implements OnClickListener { 
    Button btn_secondpage; 
    public static final String TAG = "abcd"; 

    public MainController(Button btn_secondpage) { 
     this.btn_secondpage=btn_secondpage; 
     Log.i(TAG, "inside mainController constructor"); // printing (2nd) 
    } 

    @Override 
    public void onClick(View v) { 
     Log.i(TAG, "inside public void onClick before intent");      // printing(3rd) 
     Intent intent = new Intent("com.testandroidproject.view.SecondActivity"); 
     Log.i(TAG, "inside public void onClick after intent");      // printing(4th) 
     startActivity(intent); 
     Log.i(TAG, "inside public void onClick after startActivity");    // NOT printing 

    } 

} 

AndroidManifest。XML

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="com.example.testandroidproject" 
    android:versionCode="1" 
    android:versionName="1.0" > 

    <uses-sdk 
     android:minSdkVersion="21" 
     android:targetSdkVersion="21" /> 

    <application 
     android:allowBackup="true" 
     android:icon="@drawable/ic_launcher" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme" > 
     <activity 
      android:name="com.testandroidproject.view.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="com.testandroidproject.view.SecondActivity" 
      android:label="@string/title_activity_second" > 
      <intent-filter> 
       <action android:name="com.testandroidproject.view.SecondActivity" />  

       <category android:name="android.intent.category.DEFAULT" /> 
      </intent-filter> 
     </activity> 
    </application> 

</manifest> 

logcat的

04-01 00:10:38.344: I/abcd(1764): inside oncreate 
04-01 00:10:38.345: I/abcd(1764): inside mainController constructor 
04-01 00:10:38.370: D/OpenGLRenderer(1764): Render dirty regions requested:  true 
04-01 00:10:38.374: D/(1764): HostConnection::get() New Host Connection established 0xa5f43380, tid 1764 
04-01 00:10:38.375: D/Atlas(1764): Validating map... 
04-01 00:10:38.399: D/(1764): HostConnection::get() New Host Connection established 0xad480dc0, tid 1780 
04-01 00:10:38.401: I/OpenGLRenderer(1764): Initialized EGL, version 1.4 
04-01 00:10:38.446: D/OpenGLRenderer(1764): Enabling debug mode 0 
04-01 00:10:38.546: W/EGL_emulation(1764): eglSurfaceAttrib not implemented 
04-01 00:10:38.546: W/OpenGLRenderer(1764): Failed to set EGL_SWAP_BEHAVIOR on surface 0xa5f46240, error=EGL_SUCCESS 
04-01 00:11:51.749: I/abcd(1764): inside oncreate 
04-01 00:11:51.754: I/abcd(1764): inside mainController constructor 
04-01 00:11:51.896: W/EGL_emulation(1764): eglSurfaceAttrib not implemented 
04-01 00:11:51.896: W/OpenGLRenderer(1764): Failed to set EGL_SWAP_BEHAVIOR on surface 0xa5f46240, error=EGL_SUCCESS 
04-01 00:11:55.658: I/abcd(1764): inside public void onClick before intent 
04-01 00:11:55.658: I/abcd(1764): inside public void onClick after intent 
04-01 00:11:55.658: D/AndroidRuntime(1764): Shutting down VM 
04-01 00:11:55.658: D/AndroidRuntime(1764): --------- beginning of crash 
04-01 00:11:55.658: E/AndroidRuntime(1764): FATAL EXCEPTION: main 
04-01 00:11:55.658: E/AndroidRuntime(1764): Process: com.example.testandroidproject, PID: 1764 
04-01 00:11:55.658: E/AndroidRuntime(1764): java.lang.NullPointerException: Attempt to invoke virtual method 'android.app.ActivityThread$ApplicationThread android.app.ActivityThread.getApplicationThread()' on a null object reference 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at android.app.Activity.startActivityForResult(Activity.java:3736) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at android. app.Activity.startActivityForResult(Activity.java:3697) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at android.app.Activity.startActivity(Activity.java:4007) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at android.app.Activity.startActivity(Activity.java:3975) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at com.testandroidproject.controller.MainController.onClick(MainController.java:24) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at android.view.View.performClick(View.java:4756) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at android.view.View$PerformClick.run(View.java:19749) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at android.os.Handler.handleCallback(Handler.java:739) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at android.os.Handler.dispatchMessage(Handler.java:95) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at android.os.Looper.loop(Looper.java:135) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at android.app.ActivityThread.main(ActivityThread.java:5221) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at java.lang.reflect.Method.invoke(Native Method) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at java.lang.reflect.Method.invoke(Method.java:372) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at com.and roid.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
04-01 00:11:55.658: E/AndroidRuntime(1764):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 
04-01 00:11:55.857: I/art(1764): Background sticky concurrent mark sweep GC freed 2383(175KB) AllocSpace objects, 1(81KB) LOS objects, 29% free, 794KB/1135KB, paused 1.621ms total 150.498ms 
04-01 00:12:09.406: I/Process(1764): Sending signal. PID: 1764 SIG: 9 

enter image description here

Answer 1

在MainController类onClick()你创建Intent对象时出错，请用此更改Intent intent = new Intent(btn_secondpage.getContext(), SecondActivity.class);

请确保您的MainController不是Activity的子类，这会导致错误。因为现在您的活动不是Context的子类，所以无法拨打startActivity()。通过传递按钮启动活动使用上下文

public class MainController implements OnClickListener{ 
    //............ 
@Override 
public void onClick(View v) { 
    Intent intent = new Intent(btn_secondpage.getContext(), SecondActivity.class); 
    btn_secondpage.getContext().startActivity(intent); 
}