求助！为什么会Unable to instantiate activity ComponentInfo

[巴特桑]

小弟才接触android开发不久
现在想要写一个调用手机红外端口遥控空调的小APP
在ADT中没有显示错误，但是真机运行报如下错误：

07-03 10:25:46.268: D/AndroidRuntime(1058): Shutting down VM
07-03 10:25:46.278: W/dalvikvm(1058): threadid=1: thread exiting with uncaught exception (group=0xb1a84ba8)
07-03 10:25:46.298: E/AndroidRuntime(1058): FATAL EXCEPTION: main
07-03 10:25:46.298: E/AndroidRuntime(1058): Process: com.studiocean.m_remote, PID: 1058
07-03 10:25:46.298: E/AndroidRuntime(1058): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.studiocean.m_remote/com.studiocean.m_remote.MainActivity}: java.lang.NullPointerException
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at android.app.ActivityThread.access$800(ActivityThread.java:135)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at android.os.Handler.dispatchMessage(Handler.java:102)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at android.os.Looper.loop(Looper.java:136)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at android.app.ActivityThread.main(ActivityThread.java:5017)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at java.lang.reflect.Method.invokeNative(Native Method)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at java.lang.reflect.Method.invoke(Method.java:515)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at dalvik.system.NativeStart.main(Native Method)
07-03 10:25:46.298: E/AndroidRuntime(1058): Caused by: java.lang.NullPointerException
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at android.app.Activity.findViewById(Activity.java:1884)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at com.studiocean.m_remote.MainActivity.<init>(MainActivity.java:17)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at java.lang.Class.newInstanceImpl(Native Method)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at java.lang.Class.newInstance(Class.java:1208)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
07-03 10:25:46.298: E/AndroidRuntime(1058): 	... 11 more
07-03 10:26:35.578: I/Process(1058): Sending signal. PID: 1058 SIG: 9

以下是源代码：

MainActivity.java

package com.studiocean.m_remote;

import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class MainActivity extends Activity {
	
	private boolean isACOn = false;
	
	TextView statusDisplay = (TextView)findViewById(R.id.statusDis);
	
	@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (savedInstanceState == null) {
            getFragmentManager().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 IrHandler irHandler = new IrHandler(getBaseContext());
    
    public void onPowerSwitchClicked(View view) {
    	if (!isACOn) statusDisplay.setVisibility(View.VISIBLE);
    		else statusDisplay.setVisibility(View.INVISIBLE);
    	irHandler.setStrCode("POWER_SWITCH");
    }
}

IrHandler.java

package com.studiocean.m_remote;

import android.content.Context;
import android.hardware.ConsumerIrManager;

public class IrHandler {
	
	String tmpStrCode = "";
	Context tmpCtx;
	
	public IrHandler() {
	}
	
	public IrHandler(Context context) {
		tmpCtx = context;
	}
	
	ConsumerIrManager consumerIrManager = (ConsumerIrManager) tmpCtx.getSystemService(Context.CONSUMER_IR_SERVICE);
	
	public void setStrCode(String strCode) {
		tmpStrCode = strCode;
		moduleStr();
	}
	
	public void moduleStr() {
		switch (tmpStrCode)
		{
			case "POWER_SWITCH":
				consumerIrManager.transmit(38400, new int[] {1901, 4453, 625, 1614, 625, 1588, 625, 1614, 625, 442, 625, 442, 625, 468, 625, 442, 625, 494, 572, 1614, 625, 1588, 625, 1614, 625, 494, 572, 442, 651, 442, 625, 442, 625, 442, 625, 1614, 625, 1588, 651, 1588, 625, 442, 625, 494, 598, 442, 625, 442, 625, 520, 572, 442, 625, 442, 625, 442, 651, 1588, 625, 1614, 625, 1588, 625, 1614, 625, 1588, 625, 48958});
				break;
			case "MODE_SELECTION":
				consumerIrManager.transmit(38000, null);
				break;
			case "TEMPERATURE_UP":
				consumerIrManager.transmit(38000, null);
				break;
			case "TEMPERATURE_DOWN":
				consumerIrManager.transmit(38000, null);
				break;
			default:
				break;
		}
	}
}

不知是为何？

[巴特桑]

引用 1 楼 rtyou1234 的回复:

TextView statusDisplay = (TextView)findViewById(R.id.statusDis); 把findviewbyid放到setContentView(R.layout.activity_main);后面，布局都还没加载，怎么找到view

引用 2 楼 u012861744 的回复:

初始的时候顺序错了，界面还没有加载进来，不要给他任何东西！

刚刚又试了一下，貌似只能把

private IrHandler irHandler = new IrHandler(getBaseContext());

也删掉才能显示界面，那是我的IrHandler写得有问题吗？

[逍遥笑]

TextView statusDisplay = (TextView)findViewById(R.id.statusDis); 把findviewbyid放到setContentView(R.layout.activity_main);后面，布局都还没加载，怎么找到view

[Nelson.Feng]

初始的时候顺序错了，界面还没有加载进来，不要给他任何东西！

[巴特桑]

引用 1 楼 rtyou1234 的回复:

TextView statusDisplay = (TextView)findViewById(R.id.statusDis); 把findviewbyid放到setContentView(R.layout.activity_main);后面，布局都还没加载，怎么找到view

引用 2 楼 u012861744 的回复:

初始的时候顺序错了，界面还没有加载进来，不要给他任何东西！

两位大大： 好像我这版本的ADT初始一个项目之后就会有fragment，所以是我把界面布局直接放在fragment_main.xml里面的，现在我将TextView statusDisplay = (TextView)rootView.findViewById(R.id.statusDis);一句放在onCreateView下的View rootView = inflater.inflate(R.layout.fragment_main, container, false);后面，但ADT提示statusDisplay is not used（在后面的onPowerSwitchClicked里面我有调用啊）？ 然后我尝试把

TextView statusDisplay = (TextView)rootView.findViewById(R.id.statusDis);

public void onPowerSwitchClicked(View view) {
    	if (!isACOn) statusDisplay.setVisibility(View.VISIBLE);
    		else statusDisplay.setVisibility(View.INVISIBLE);
    	irHandler.setStrCode("POWER_SWITCH");

这两段都删掉，结果LogCat还是报一样的错误信息啊 是因为我的IrHandler写的有问题吗？

[夏布旅人]

把源代码发过来我帮你看看。

[zhangweia]

android开发5年经验了，你的问题可以联系，我帮你解决。 775925302，另外我也正在研究红外控制的模块，可以一起讨论