java - 为什么我的应用程序 "unfortunately stop".我想要的只是一些简单的按钮

Question

这是我的第一个应用程序。我所需要的只是五个按钮，其中两个用于调用某些电话号码(到目前为止只创建了一个)，三个按钮用于将用户带到某个 URL。我没有收到任何错误或警告，也没有任何有关如何导航 LogCat 的说明。

日志猫:

10-08 14:41:40.716: D/AndroidRuntime(793): Shutting down VM
10-08 14:41:40.716: W/dalvikvm(793): threadid=1: thread exiting with uncaught exception (group=0x41465700)
10-08 14:41:40.777: E/AndroidRuntime(793): FATAL EXCEPTION: main
10-08 14:41:40.777: E/AndroidRuntime(793): java.lang.RuntimeException: Unable to start activity ComponentInfo{acps.mhs/acps.mhs.MainActivity}: java.lang.NullPointerException
10-08 14:41:40.777: E/AndroidRuntime(793):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
10-08 14:41:40.777: E/AndroidRuntime(793):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
10-08 14:41:40.777: E/AndroidRuntime(793):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
10-08 14:41:40.777: E/AndroidRuntime(793):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
10-08 14:41:40.777: E/AndroidRuntime(793):  at android.os.Handler.dispatchMessage(Handler.java:99)
10-08 14:41:40.777: E/AndroidRuntime(793):  at android.os.Looper.loop(Looper.java:137)
10-08 14:41:40.777: E/AndroidRuntime(793):  at android.app.ActivityThread.main(ActivityThread.java:5103)
10-08 14:41:40.777: E/AndroidRuntime(793):  at java.lang.reflect.Method.invokeNative(Native Method)
10-08 14:41:40.777: E/AndroidRuntime(793):  at java.lang.reflect.Method.invoke(Method.java:525)
10-08 14:41:40.777: E/AndroidRuntime(793):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
10-08 14:41:40.777: E/AndroidRuntime(793):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-08 14:41:40.777: E/AndroidRuntime(793):  at dalvik.system.NativeStart.main(Native Method)
10-08 14:41:40.777: E/AndroidRuntime(793): Caused by: java.lang.NullPointerException
10-08 14:41:40.777: E/AndroidRuntime(793):  at acps.mhs.MainActivity.onCreate(MainActivity.java:25)
10-08 14:41:40.777: E/AndroidRuntime(793):  at android.app.Activity.performCreate(Activity.java:5133)
10-08 14:41:40.777: E/AndroidRuntime(793):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
10-08 14:41:40.777: E/AndroidRuntime(793):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
10-08 14:41:40.777: E/AndroidRuntime(793):  ... 11 more
10-08 14:42:19.696: I/Process(793): Sending signal. PID: 793 SIG: 9

Mainactivity.java

package acps.mhs;

import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity implements View.OnClickListener {

    Button mhshome, pp, mhsdir, cmhs;

    @Override
    public void onCreate(Bundle bundle) {
        super.onCreate(bundle);


        mhshome = (Button) findViewById(R.id.mhshome);
        pp = (Button) findViewById(R.id.pp);
        mhsdir = (Button) findViewById(R.id.mhsdir);
        cmhs = (Button) findViewById(R.id.cmhs);

        mhshome.setOnClickListener(this);
        pp.setOnClickListener(this);
        mhsdir.setOnClickListener(this);
        cmhs.setOnClickListener(this);
   }

   @Override
   public void onClick(View v) {
       switch(v.getId()) {

       case R.id.mhshome:
             Uri uri = Uri.parse("http://www2.k12albemarle.org/school/mohs/Pages/default.aspx");
             Intent intent = new Intent(Intent.ACTION_VIEW, uri);
             startActivity(intent);
           break;


       case R.id.pp:
             Uri uri2 = Uri.parse("http://www2.k12albemarle.org/school/MOHS/Pages/Directory.aspx");
             Intent intent2 = new Intent(Intent.ACTION_VIEW, uri2);
             startActivity(intent2);
           break; 

       case R.id.mhsdir:
             Uri uri3 = Uri.parse("http://www2.k12albemarle.org/school/MOHS/Pages/Directory.aspx");
             Intent intent3 = new Intent(Intent.ACTION_VIEW, uri3);
             startActivity(intent3);
               break;

       case R.id.cmhs:
            Intent callIntent = new Intent(Intent.ACTION_CALL);
            callIntent.setData(Uri.parse("tel:1234567890"));
            startActivity(callIntent);
               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;
    }

}

activity_main.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=".MainActivity" >

    <Button
        android:id="@+id/pp"
        style="@style/AppBaseTheme"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/mhshome"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="16dp"
        android:text="@string/pp"/>

    <Button
        android:id="@+id/mhshome"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="26dp"
        android:onClick="onClick"
        android:text="@string/mhshome" />

    <Button
        android:id="@+id/mhsdir"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/pp"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="20dp"
        android:text="@string/mhsdir" />

    <Button
        android:id="@+id/cmhs"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/mhsdir"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="20dp"
        android:text="@string/callmhs" />

</RelativeLayout>

我确信这将是非常简单的事情。请为我指明正确的方向。

Answer 1

您需要调用 setContentView(R.layout.activity_main) :) 这就是 findViewById 在您的 View 上返回 null 的原因。