LogCat是压倒性的，我不知道该怎么办...应用程序关闭打开？

Question

这里是java文件，使用的唯一一个...如果我知道什么是错误的意思我能做到这一点我自己

package tip.calculator; 


import android.os.Bundle; 
import android.app.Activity; 
import android.view.View.OnClickListener; 
import android.widget.EditText; 
import android.widget.TextView; 
import android.view.View; 
import android.widget.Button; 




public class TipCalculator extends Activity 
{ 

private Button enter; 
EditText myEditField = (EditText) findViewById(R.id.percentText); 
final EditText myEditField2 = (EditText) findViewById(R.id.billText); 

float percentage = 0; 
float percentageInp = 0; 
float billAmount = 0; 
double output = 0; 
String output1 = ""; 
Button clearButton = (Button) findViewById(R.id.clearButton); 

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

    myEditField = (EditText) findViewById(R.id.percentText); 
    enter = (Button)findViewById(R.id.button1); 


    enter.setOnClickListener(new OnClickListener() { 


     public void onClick(View v) { 
      TextView textView; 
      TextView errors; 
      textView = (TextView) findViewById(R.id.textView1); 
      errors = (TextView) findViewById(R.id.errorText);    
      for(;;){ 

      if(myEditField == null){ 
       break; 
      } 

      if(myEditField2 == null){ 
       break; 
      } 

      } 

      percentageInp = Float.parseFloat(myEditField.getText().toString()); 
      billAmount = Float.parseFloat(myEditField2.getText().toString()); 

      percentage = ((float)percentageInp /100); 

      output = (double)(billAmount * percentage); 

      double result = output * 100; 
      result = Math.round(result); 
      result = result/100; 

      output1 = Double.toString(result); 

      textView.setText(output1 + " $"); 

     } 
    }); 

    clearButton.setOnClickListener(new OnClickListener() { 

     public void onClick(View arg0) { 

      percentage = 0; 
      output = 0; 
      output1 = ""; 
      TextView textView; 

      textView = (TextView) findViewById(R.id.textView1); 

      textView.setText(""); 

      percentageInp = 0; 
      billAmount = 0; 

      myEditField.setText(""); 
      myEditField2.setText(""); 


     } 


    }); 
} 
} 

这是logcat的，我不知道是什么意思的错误或如何接近他们......注：以上只是产生的应用程序打开时，然后它崩溃

08-01 15:37:43.934: E/Trace(671): error opening trace file: No such file or directory (2) 
08-01 15:37:44.704: E/AndroidRuntime(671): FATAL EXCEPTION: main 
08-01 15:37:44.704: E/AndroidRuntime(671): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{tip.calculator/tip.calculator.TipCalculator}: java.lang.NullPointerException 
08-01 15:37:44.704: E/AndroidRuntime(671): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983) 
08-01 15:37:44.704: E/AndroidRuntime(671): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
08-01 15:37:44.704: E/AndroidRuntime(671): at android.app.ActivityThread.access$600(ActivityThread.java:130) 
08-01 15:37:44.704: E/AndroidRuntime(671): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
08-01 15:37:44.704: E/AndroidRuntime(671): at android.os.Handler.dispatchMessage(Handler.java:99) 
08-01 15:37:44.704: E/AndroidRuntime(671): at android.os.Looper.loop(Looper.java:137) 
08-01 15:37:44.704: E/AndroidRuntime(671): at android.app.ActivityThread.main(ActivityThread.java:4745) 
08-01 15:37:44.704: E/AndroidRuntime(671): at java.lang.reflect.Method.invokeNative(Native Method) 
08-01 15:37:44.704: E/AndroidRuntime(671): at java.lang.reflect.Method.invoke(Method.java:511) 
08-01 15:37:44.704: E/AndroidRuntime(671): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
08-01 15:37:44.704: E/AndroidRuntime(671): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
08-01 15:37:44.704: E/AndroidRuntime(671): at dalvik.system.NativeStart.main(Native Method) 
08-01 15:37:44.704: E/AndroidRuntime(671): Caused by: java.lang.NullPointerException 
08-01 15:37:44.704: E/AndroidRuntime(671): at android.app.Activity.findViewById(Activity.java:1825) 
08-01 15:37:44.704: E/AndroidRuntime(671): at tip.calculator.TipCalculator.<init>(TipCalculator.java:19) 
08-01 15:37:44.704: E/AndroidRuntime(671): at java.lang.Class.newInstanceImpl(Native Method) 
08-01 15:37:44.704: E/AndroidRuntime(671): at java.lang.Class.newInstance(Class.java:1319) 
08-01 15:37:44.704: E/AndroidRuntime(671): at android.app.Instrumentation.newActivity(Instrumentation.java:1053) 
08-01 15:37:44.704: E/AndroidRuntime(671): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974) 
08-01 15:37:44.704: E/AndroidRuntime(671): ... 11 more 
08-01 15:38:44.993: E/Trace(741): error opening trace file: No such file or directory (2) 
08-01 15:38:45.123: E/AndroidRuntime(741): FATAL EXCEPTION: main 
08-01 15:38:45.123: E/AndroidRuntime(741): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{tip.calculator/tip.calculator.TipCalculator}: java.lang.NullPointerException 
08-01 15:38:45.123: E/AndroidRuntime(741): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983) 
08-01 15:38:45.123: E/AndroidRuntime(741): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
08-01 15:38:45.123: E/AndroidRuntime(741): at android.app.ActivityThread.access$600(ActivityThread.java:130) 
08-01 15:38:45.123: E/AndroidRuntime(741): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
08-01 15:38:45.123: E/AndroidRuntime(741): at android.os.Handler.dispatchMessage(Handler.java:99) 
08-01 15:38:45.123: E/AndroidRuntime(741): at android.os.Looper.loop(Looper.java:137) 
08-01 15:38:45.123: E/AndroidRuntime(741): at android.app.ActivityThread.main(ActivityThread.java:4745) 
08-01 15:38:45.123: E/AndroidRuntime(741): at java.lang.reflect.Method.invokeNative(Native Method) 
08-01 15:38:45.123: E/AndroidRuntime(741): at java.lang.reflect.Method.invoke(Method.java:511) 
08-01 15:38:45.123: E/AndroidRuntime(741): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
08-01 15:38:45.123: E/AndroidRuntime(741): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
08-01 15:38:45.123: E/AndroidRuntime(741): at dalvik.system.NativeStart.main(Native Method) 
08-01 15:38:45.123: E/AndroidRuntime(741): Caused by: java.lang.NullPointerException 
08-01 15:38:45.123: E/AndroidRuntime(741): at android.app.Activity.findViewById(Activity.java:1825) 
08-01 15:38:45.123: E/AndroidRuntime(741): at tip.calculator.TipCalculator.<init>(TipCalculator.java:19) 
08-01 15:38:45.123: E/AndroidRuntime(741): at java.lang.Class.newInstanceImpl(Native Method) 
08-01 15:38:45.123: E/AndroidRuntime(741): at java.lang.Class.newInstance(Class.java:1319) 
08-01 15:38:45.123: E/AndroidRuntime(741): at android.app.Instrumentation.newActivity(Instrumentation.java:1053) 
08-01 15:38:45.123: E/AndroidRuntime(741): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974) 
08-01 15:38:45.123: E/AndroidRuntime(741): ... 11 more 

Answer 1

的问题是这些线路正在使用初始化你TipCalculator类的成员字段：

EditText myEditField = (EditText) findViewById(R.id.percentText); 
final EditText myEditField2 = (EditText) findViewById(R.id.billText); 
Button clearButton = (Button) findViewById(R.id.clearButton); 

在调用setContentView之前，不能使用findViewById。替换上面：

EditText myEditField; 
EditText myEditField2; 
Button clearButton; 

，然后调用setContentView后的某个位置添加这onCreate：

myEditField = (EditText) findViewById(R.id.percentText); 
myEditField2 = (EditText) findViewById(R.id.billText); 
clearButton = (Button) findViewById(R.id.clearButton); 

附：解释logcat输出的方法是查找最后一个“由...引发”行并读取该堆栈跟踪。所有那些与之前无关的诊断任务都是无关紧要的。