java.lang.RuntimeException:尝试构建我的应用程序时无法实例化活动

我一直在研究mu，首先是我喜欢将其视为合法应用的东西，不过我已经进入了一个领域，我已经在很多论坛上浏览了一下，其中没有一个论坛似乎有适合我的解决方案。当主活动出现问题时，会发生错误。我没有任何其他活动的，我已经疯了，所以我不知道是什么导致了这个错误

public class MainActivity extends ActionBarActivity
    implements NavigationDrawerFragment.NavigationDrawerCallbacks {

final String TAG = "made it";

Timer queentime,dronetimer;
float droneout;
double  addtime = 0.01;
double injectout =0.0;



TextView injectscreen = (TextView) findViewById(R.id.tvinject);
TextView dronescreen = (TextView) findViewById(R.id.tvdrone);

/**
 * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
 */
private NavigationDrawerFragment mNavigationDrawerFragment;

/**
 * Used to store the last screen title. For use in {@link #restoreActionBar()}.
 */
private CharSequence mTitle;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
   /* Timer queentime = new Timer();
    Timer dronetimer = new Timer();*/
    Log.i(TAG, "made it");


    mNavigationDrawerFragment = (NavigationDrawerFragment)
            getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
    mTitle = getTitle();

    // Set up the drawer.
    mNavigationDrawerFragment.setUp(
            R.id.navigation_drawer,
            (DrawerLayout) findViewById(R.id.drawer_layout));
}

/*class injectup extends TimerTask{
    @Override
    public void run() {
        injectout = injectout+addtime;
        injectscreen.setText((int) injectout);
    }
}

public void injectclick(View view){
    queentime.schedule(new injectup(), 10);




}


public void droneclick(View view){





}*/









@Override
public void onNavigationDrawerItemSelected(int position) {
    // update the main content by replacing fragments
    FragmentManager fragmentManager = getSupportFragmentManager();
    fragmentManager.beginTransaction()
            .replace(R.id.container, PlaceholderFragment.newInstance(position + 1))
            .commit();
}

public void onSectionAttached(int number) {
    switch (number) {
        case 1:
            mTitle = getString(R.string.title_section1);
            break;
        case 2:
            mTitle = getString(R.string.title_section2);
            break;
        case 3:
            mTitle = getString(R.string.title_section3);
            break;
    }
}

public void restoreActionBar() {
    ActionBar actionBar = getSupportActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
    actionBar.setDisplayShowTitleEnabled(true);
    actionBar.setTitle(mTitle);
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    if (!mNavigationDrawerFragment.isDrawerOpen()) {
        // Only show items in the action bar relevant to this screen
        // if the drawer is not showing. Otherwise, let the drawer
        // decide what to show in the action bar.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        restoreActionBar();
        return true;
    }
    return super.onCreateOptionsMenu(menu);
}

@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();

    //noinspection SimplifiableIfStatement
    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 {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    private static final String ARG_SECTION_NUMBER = "section_number";

    /**
     * Returns a new instance of this fragment for the given section
     * number.
     */
    public static PlaceholderFragment newInstance(int sectionNumber) {
        PlaceholderFragment fragment = new PlaceholderFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return 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;
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        ((MainActivity) activity).onSectionAttached(
                getArguments().getInt(ARG_SECTION_NUMBER));
    }
}

}

这些导入都很好，我先检查了它们，看看我是否在那里塞满了一些东西。我还注释了我所做的函数，以防它们导致问题

如果你感兴趣的话，这是我的进口货

package com.first.cameron.sctimer;

import android.app.Activity;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.content.Context;
import android.os.Build;
import android.os.Bundle;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.support.v4.widget.DrawerLayout;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import android.util.Log;
import java.util.Timer;
import java.util.TimerTask;

这是完整的日志cat数据

   --------- beginning of crash
01-08 12:08:15.157    2143-2143/com.first.cameron.sctimer E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.first.cameron.sctimer, PID: 2143
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.first.cameron.sctimer/com.first.cameron.sctimer.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
            at android.app.Activity.findViewById(Activity.java:2071)
            at com.first.cameron.sctimer.MainActivity.<init>(MainActivity.java:35)
            at java.lang.reflect.Constructor.newInstance(Native Method)
            at java.lang.Class.newInstance(Class.java:1572)
            at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

-----------崩溃开始
01-08 12:08:15.157 2143-2143/com.first.cameron.sctimer E/AndroidRuntime﹕ 致命异常：主
进程：com.first.cameron.sctimer，PID:2143
java.lang.RuntimeException:无法实例化活动组件信息{com.first.cameron.sctimer/com.first.cameron.sctimer.MainActivity}:java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“android.view.view android.view.Window.findViewById（int）”
在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2209）上
在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2360）上
在android.app.ActivityThread.access$800（ActivityThread.java:144）
在android.app.ActivityThread$H.handleMessage（ActivityThread.java:1278）
位于android.os.Handler.dispatchMessage（Handler.java:102）
位于android.os.Looper.loop（Looper.java:135）
位于android.app.ActivityThread.main（ActivityThread.java:5221）
位于java.lang.reflect.Method.invoke（本机方法）
位于java.lang.reflect.Method.invoke（Method.java:372）
在com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run（ZygoteInit.java:899）上
位于com.android.internal.os.ZygoteInit.main（ZygoteInit.java:694）
原因：java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“android.view.view android.view.Window.findViewById（int）”
在android.app.Activity.findviewbyd（Activity.java:2071）上
位于com.first.cameron.sctimer.MainActivity。（MainActivity.java:35）
位于java.lang.reflect.Constructor.newInstance（本机方法）
位于java.lang.Class.newInstance（Class.java:1572）
位于android.app.Instrumentation.newActivity（Instrumentation.java:1065）
在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2199）上
在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2360）上
在android.app.ActivityThread.access$800（ActivityThread.java:144）
在android.app.ActivityThread$H.handleMessage（ActivityThread.java:1278）
位于android.os.Handler.dispatchMessage（Handler.java:102）
位于android.os.Looper.loop（Looper.java:135）
位于android.app.ActivityThread.main（ActivityThread.java:5221）
位于java.lang.reflect.Method.invoke（本机方法）
位于java.lang.reflect.Method.invoke（Method.java:372）
在com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run（ZygoteInit.java:899）上
位于com.android.internal.os.ZygoteInit.main（ZygoteInit.java:694）

我觉得谷歌应该更准确地知道错误的来源，因为它的含义很广泛，这使得很难找出问题所在。我也在运行android studio，如果这会有什么不同的话

---

提前感谢，如果这是非常明显的问题，请道歉。

将这一行移到setContentView（）之后的onCreate方法

---

您必须在onCreate方法中实例化TextView

TextView injectscreen;
TextView dronescreen;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    injectscreen = (TextView) findViewById(R.id.tvinject);
    dronescreen = (TextView) findViewById(R.id.tvdrone);
....
}

TextView injectscreen;
TextView dronescreen;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    injectscreen = (TextView) findViewById(R.id.tvinject);
    dronescreen = (TextView) findViewById(R.id.tvdrone);
....
}