Question

我在Android应用程序中的主要活动有些问题。该应用无法打开。请帮助。感谢

package com.example.sgdriverdiary;

import android.app.Activity;
import android.content.Intent; 
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;

public class MainActivity extends Activity implements OnClickListener {
   Button button2, button3, button4, button1;
   @Override
   public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
     button2 = (Button) findViewById(R.id.button2);
     button3 = (Button) findViewById(R.id.button3);
     button4 = (Button) findViewById(R.id.button4);
     button1 = (Button) findViewById(R.id.button1);
     button2.setOnClickListener((OnClickListener) this);
     button3.setOnClickListener(this);
     button4.setOnClickListener(this);
     button1.setOnClickListener(this);
    //if (savedInstanceState == null) {
        //getSupportFragmentManager().beginTransaction()
            //  .add(R.id.container, new PlaceholderFragment()).commit();
    //}
}

@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);
}

/**
 * A placeholder fragment containing a simple view.
 */
/*public static class PlaceholderFragment extends Fragment {

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container,
                false);
        return rootView;
    }
}*/
/*public void rate(View view){
    Intent intent = new Intent(this, Rate.class);
    startActivity(intent);
}
public void cal(View view){
    Intent intent = new Intent(this, Cal.class);
    startActivity(intent);
}
public void search(View view){
    Intent intent = new Intent(this,Search.class);
    startActivity(intent);
}*/
public void onClick(View v){
    Intent intent = new Intent();

    if(v == button3)
    {
        intent.setClass(this, Cal.class);
    }
    else if(v == button1)
    {
        intent.setClass(this, Rate.class);
    }
    else if(v == button4)
    {
        intent.setClass(this, Search.class);
    }
    /*else if(v== button2)
    {
        intent.setClass(this, Record.class);
    }*/
    else{
        return;
    }
    startActivity(intent);
}
}

这是log cat

05-18 12:28:11.753: E/AndroidRuntime(1048): FATAL EXCEPTION: main
05-18 12:28:11.753: E/AndroidRuntime(1048): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.sgdriverdiary/com.example.sgdriverdiary.MainActivity}: java.lang.NullPointerException
05-18 12:28:11.753: E/AndroidRuntime(1048):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at android.os.Looper.loop(Looper.java:137)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at android.app.ActivityThread.main(ActivityThread.java:4424)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at java.lang.reflect.Method.invokeNative(Native Method)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at java.lang.reflect.Method.invoke(Method.java:511)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at dalvik.system.NativeStart.main(Native Method)
05-18 12:28:11.753: E/AndroidRuntime(1048): Caused by: java.lang.NullPointerException
05-18 12:28:11.753: E/AndroidRuntime(1048):     at com.example.sgdriverdiary.MainActivity.onCreate(MainActivity.java:25)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at android.app.Activity.performCreate(Activity.java:4465)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
05-18 12:28:11.753: E/AndroidRuntime(1048):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
05-18 12:28:11.753: E/AndroidRuntime(1048):     ... 11 more
05-18 12:28:11.913: I/dalvikvm(1048): threadid=3: reacting to signal 3
05-18 12:28:11.943: I/dalvikvm(1048): Wrote stack traces to '/data/anr/traces.txt'
05-18 12:28:12.284: I/dalvikvm(1048): threadid=3: reacting to signal 3
05-18 12:28:12.294: I/dalvikvm(1048): Wrote stack traces to '/data/anr/traces.txt'
05-18 12:33:11.793: I/Process(1048): Sending signal. PID: 1048 SIG: 9

Answer 1

不要那样使用onClick - 而且您不需要实施onClickListener。

在您的XML文件中，您可以设置此属性：android:onClick="whatever"，然后您不需要所有setOnClickListener内容。只需使用

public void whatever (View v){
//do your stuff
}

Answer 2

试试这个：

如果您的button = (Button) findViewById(R.id.button2);

然后setOnClickListener()为

button.setOnClickListener(new View.OnClickListener() {
      public void onClick(View v) {
       // Do something in response to button click
   }
 });

这是在xml中设置android:onClick侦听器的首选方法。

我的主应用程序菜单无法打开

2 个答案: