-1

Eclipse 在我的代码中没有发现任何错误，但是当我尝试在模拟器上运行该应用程序时，它会打开然后立即崩溃。Logcat 给了我一个模糊的 nullPointerException 错误。我可以注释掉 onKeyDown 方法，然后它运行得很好。但是当然，我不能使用返回键返回，它只会关闭应用程序。

我的代码如下：

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.ViewFlipper;

public class MainActivity extends Activity {
static String[] items = {"Campaign", "Multiplayer", "Zombies"};

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ListView listView = (ListView) findViewById(R.id.listview);
        final ViewFlipper viewflipper = (ViewFlipper)   findViewById(R.id.viewflipper1);
        listView.setAdapter(new BaseAdapter(){
            public int getCount() {
            return items.length;
            }
            public Object getItem(int position) {
            return items[position];
            }
            public long getItemId(int position) {
            return position;
            }
            public View getView(int position, View convertView, ViewGroup parent) {
                LayoutInflater inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
                View view = inflater.inflate(R.layout.list_row, null);
                TextView textView = (TextView) view.findViewById(R.id.TextView01);
                textView.setText(items[position]);
                textView.setTextColor(Color.rgb(255,106,0));
                textView.setTextSize(24);
                TextView textView1 = (TextView) findViewById(R.id.textView1);
                textView1.setTextColor(Color.rgb(255,106,0));
            return view;
            }});

            listView.setOnItemClickListener(new OnItemClickListener(){
              public void onItemClick(AdapterView<?> a, View v, int position, long id) {
                 if (position == 0) {
                     viewflipper.showNext();
                 }if (position == 1) {
                     viewflipper.showNext();
                     viewflipper.showNext();
                 }if (position == 2) {
                     viewflipper.showNext();
                     viewflipper.showNext();
                     viewflipper.showNext();
                 }}   

        });    

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;  
    }

    ViewFlipper viewflipper = (ViewFlipper) findViewById(R.id.viewflipper1);

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event)  {
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
             if(viewflipper.getDisplayedChild() == 0){
                 viewflipper.showPrevious();
              }if(viewflipper.getDisplayedChild() == 1){
                 viewflipper.showPrevious();
                 viewflipper.showPrevious();
              }if(viewflipper.getDisplayedChild() == 2){
                 viewflipper.showPrevious();
                 viewflipper.showPrevious();
                 viewflipper.showPrevious();
              }
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }

};

我的Logcat如下：

01-21 11:38:46.151: E/AndroidRuntime(760): FATAL EXCEPTION: main

01-21 11:38:46.151: E/AndroidRuntime(760): java.lang.RuntimeException: Unable to instantiate activity 
ComponentInfo{com.example.blackopsiiexperience/com.example.blackopsiiexperience.MainActivity}: java.lang.NullPointerException

01-21 11:38:46.151: E/AndroidRuntime(760):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)

01-21 11:38:46.151: E/AndroidRuntime(760):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)

01-21 11:38:46.151: E/AndroidRuntime(760):  at android.app.ActivityThread.access$600(ActivityThread.java:141)

01-21 11:38:46.151: E/AndroidRuntime(760):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)

01-21 11:38:46.151: E/AndroidRuntime(760):  at android.os.Handler.dispatchMessage(Handler.java:99)

01-21 11:38:46.151: E/AndroidRuntime(760):  at android.os.Looper.loop(Looper.java:137)

01-21 11:38:46.151: E/AndroidRuntime(760):  at android.app.ActivityThread.main(ActivityThread.java:5039)

01-21 11:38:46.151: E/AndroidRuntime(760):  at java.lang.reflect.Method.invokeNative(Native Method)

01-21 11:38:46.151: E/AndroidRuntime(760):  at java.lang.reflect.Method.invoke(Method.java:511)

01-21 11:38:46.151: E/AndroidRuntime(760):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)

01-21 11:38:46.151: E/AndroidRuntime(760):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)

01-21 11:38:46.151: E/AndroidRuntime(760):  at dalvik.system.NativeStart.main(Native Method)

01-21 11:38:46.151: E/AndroidRuntime(760): Caused by: java.lang.NullPointerException

01-21 11:38:46.151: E/AndroidRuntime(760):  at android.app.Activity.findViewById(Activity.java:1839)

01-21 11:38:46.151: E/AndroidRuntime(760):  at com.example.blackopsiiexperience.MainActivity.<init>(MainActivity.java:73)

01-21 11:38:46.151: E/AndroidRuntime(760):  at java.lang.Class.newInstanceImpl(Native Method)

01-21 11:38:46.151: E/AndroidRuntime(760):  at java.lang.Class.newInstance(Class.java:1319)

01-21 11:38:46.151: E/AndroidRuntime(760):  at android.app.Instrumentation.newActivity(Instrumentation.java:1054)

01-21 11:38:46.151: E/AndroidRuntime(760):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)

01-21 11:38:46.151: E/AndroidRuntime(760):  ... 11 more


Any suggestions?
4

1 回答 1

6

移动

ViewFlipper viewflipper = (ViewFlipper) findViewById(R.id.viewflipper1);

为 Activity 设置布局后，在 Activity 的 onCreate 内

编辑 ：

将 Viewflipper 声明为类级别字段以通过类而不是方法级别访问它：

public class MainActivity extends Activity {
static String[] items = {"Campaign", "Multiplayer", "Zombies"};
 ListView listView;
 ViewFlipper viewflipper;  //<<<< declare here
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        listView = (ListView) findViewById(R.id.listview);
        viewflipper = (ViewFlipper)   findViewById(R.id.viewflipper1);
        //your code here.....
于 2013-01-21T18:55:17.213 回答