Question

在我的应用程序中，第一个屏幕是一个列表，当您单击一次它就可以了但如果，我的错误或其他什么，您在加载应用程序崩溃之前单击两次或更多次。我一直在做一些研究，但我没有找到任何东西。我发布了我的代码：

    @Override
public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);
    setContentView(R.layout.firstscreen);
    // Set title
    getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE,
            R.layout.mainheader);

    // Get Arguments
    Bundle extras = getIntent().getExtras();
    if (extras != null) {
        app = extras.getString("app");
    }

    //Set simulation date   
    TextView date = (TextView) findViewById(R.id.date);
    date.setText(convertDateToString());
    // set the list adapter: ListView myList =
    ListView lv = (ListView) findViewById(R.id.list);
    DataBaseAccess ddbb = new DataBaseAccess();
    //Download the data from a database
    lv.setAdapter(new MyAdapter(this, R.layout.listitem, myLines,
            flowAlarm, precAlarm));
    lv.setTextFilterEnabled(true);
    lv.setOnItemClickListener(new OnItemClickListener() {

        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            Intent i = new Intent(Main.this, ShowGraph.class);
            String[] obj = list.split(";");
            i.putExtra("object name", obj[position]);
            i.putExtra("app name", app);
            i.putExtra("app list", list);
            startActivity(i);

        }
    });

    // Set buttons clickable
    Button exit = (Button) findViewById(R.id.exit);
    exit.setOnClickListener(this);
    Button calendar = (Button) findViewById(R.id.calendar);
    calendar.setOnClickListener(this);
}

有谁知道为什么？

我的LogCat：

02-29 13:51:27.975: E/AndroidRuntime(9082): FATAL EXCEPTION: main
02-29 13:51:27.975: E/AndroidRuntime(9082): java.lang.NullPointerException
02-29 13:51:27.975: E/AndroidRuntime(9082):at org.achartengine.chart.XYChart.toRealPoint(XYChart.java:699)
02-29 13:51:27.975: E/AndroidRuntime(9082):at org.achartengine.tools.Pan.apply(Pan.java:64)
02-29 13:51:27.975: E/AndroidRuntime(9082):at org.achartengine.TouchHandler.handleTouch(TouchHandler.java:106)
02-29 13:51:27.975: E/AndroidRuntime(9082):at org.achartengine.GraphicalView.onTouchEvent(GraphicalView.java:284)
02-29 13:51:27.975: E/AndroidRuntime(9082):at android.view.View.dispatchTouchEvent(View.java:3952)
02-29 13:51:27.975: E/AndroidRuntime(9082):at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1034)
02-29 13:51:27.975: E/AndroidRuntime(9082):at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1034)
02-29 13:51:27.975: E/AndroidRuntime(9082):at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1034)
02-29 13:51:27.975: E/AndroidRuntime(9082):at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1034)
02-29 13:51:27.975: E/AndroidRuntime(9082):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1034)
02-29 13:51:27.975: E/AndroidRuntime(9082):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1034)
02-29 13:51:27.975: E/AndroidRuntime(9082):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1711)
02-29 13:51:27.975: E/AndroidRuntime(9082):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1145)
02-29 13:51:27.975: E/AndroidRuntime(9082):     at android.app.Activity.dispatchTouchEvent(Activity.java:2096)
02-29 13:51:27.975: E/AndroidRuntime(9082):at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1695)
02-29 13:51:27.975: E/AndroidRuntime(9082):at android.view.ViewRoot.deliverPointerEvent(ViewRoot.java:2217)
02-29 13:51:27.975: E/AndroidRuntime(9082):at android.view.ViewRoot.handleMessage(ViewRoot.java:1901)
02-29 13:51:27.975: E/AndroidRuntime(9082):at android.os.Handler.dispatchMessage(Handler.java:99)
02-29 13:51:27.975: E/AndroidRuntime(9082):at android.os.Looper.loop(Looper.java:130)
02-29 13:51:27.975: E/AndroidRuntime(9082):at android.app.ActivityThread.main(ActivityThread.java:3701)
02-29 13:51:27.975: E/AndroidRuntime(9082):at java.lang.reflect.Method.invokeNative(Native Method)
02-29 13:51:27.975: E/AndroidRuntime(9082):at java.lang.reflect.Method.invoke(Method.java:507)
02-29 13:51:27.975: E/AndroidRuntime(9082):at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
02-29 13:51:27.975: E/AndroidRuntime(9082):at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:624)
02-29 13:51:27.975: E/AndroidRuntime(9082):at dalvik.system.NativeStart.main(Native Method)

ShowGraph活动oncreate：

    @Override
public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    // Get arguments
    Bundle extras = getIntent().getExtras();
    if (extras != null) {
        object = extras.getString("object name");
        app = extras.getString("app name");
        list = extras.getString("app list");
    }
    // Set title
    requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);
    setContentView(R.layout.main);
    getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE,
            R.layout.headermenu);
    // Download the info from the database

     downloadInfo(app, object);

    // set the button listeners
    listeners();
    //Set checkbox listeners
    setCheckListeners();

    // Drag Meteo
    vg = (RelativeLayout) findViewById(R.id.graph);
    vg.setOnTouchListener(new View.OnTouchListener() {
        RelativeLayout vg1 = (RelativeLayout) findViewById(R.id.graph1);

        public boolean onTouch(View v, MotionEvent event) {
            switch (event.getAction()) {
            case MotionEvent.ACTION_MOVE:
                // int x = (int) event.getX() - offset_x;
                int y = (int) event.getY() - offset_y;
                int w = getWindowManager().getDefaultDisplay().getWidth();
                int h = vg.getHeight() - 40;
                if (y < 0)
                    y = 0;
                if (y > h)
                    y = h;
                RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(
                        new ViewGroup.MarginLayoutParams(
                                RelativeLayout.LayoutParams.FILL_PARENT,
                                RelativeLayout.LayoutParams.WRAP_CONTENT));
                lp.setMargins(0, y, 0, 0);
                selected_item.setLayoutParams(lp);
                int height = vg1.getHeight();
                RelativeLayout.LayoutParams lp2 = new RelativeLayout.LayoutParams(
                        new ViewGroup.MarginLayoutParams(
                                RelativeLayout.LayoutParams.FILL_PARENT,
                                RelativeLayout.LayoutParams.WRAP_CONTENT));
                lp2.setMargins(0, 0, 0, Math.abs(vg.getHeight() - y));
                // lp2.height = y-height;
                vg1.setLayoutParams(lp2);
                break;
            default:
                break;
            }
            return true;
        }
    });
    RelativeLayout img = (RelativeLayout) findViewById(R.id.vg);
    img.setOnTouchListener(new View.OnTouchListener() {

        public boolean onTouch(View v, MotionEvent event) {
            switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                offset_x = (int) event.getX();
                offset_y = (int) event.getY();
                selected_item = v;
                break;
            default:
                break;
            }
            return false;
        }
    });
}

我尝试使用AsyncTask，因为我在这里阅读但是没有工作：

Android: Disable ListView once clicked?

Answer 1

在ShowGraph中：

if (extras != null) {
    object = extras.getString("object name");
    app = extras.getString("app name");
    list = extras.getString("app list");
}

如果您的extras为空，那么您的app也为空。那么问题就在那里

 downloadInfo(app, object); //NullPointerException

同时

1）请注意onCreate()调用一次（仅限第一次点击）。最好将“获取意图”部分移动到onStart()方法。

2）使用debbuging工具或尝试逐块隐藏注释代码，以找到NullPointerException的确切位置。

/*Like this downloadInfo(app, object); */

单击几次后应用程序崩溃

1 个答案: