我的应用程序无法启动？

Question

我不确定为什么我的应用程序无法启动，我没有收到任何错误，我也不知道发生了什么？我对android很陌生，这只是一个基本的计算器，但每次启动它都会崩溃。

***************主Activity.java**********************

package com.example.alex.myapplication;


         import android.support.v7.app.ActionBarActivity;
         import android.os.Bundle;
         import android.view.Menu;
         import android.view.MenuItem;



public class MainActivity extends ActionBarActivity {

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

     new Something(this);

}





@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.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();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
     }
    }

************************Something.java******************

package com.example.alex.myapplication;


   import android.app.Activity;
   import android.view.View;
   import android.widget.EditText;
   import android.widget.Button;




   public class Something extends Activity {


  private Button add,subtract,multiply,devide;
  private EditText editA, editB, editC;
  private double doubleA,doubleB,doubleC;

        public Something(Activity a) {

           click();


      }


       public void click(){
           editA = (EditText) findViewById(R.id.editText);
           editB = (EditText) findViewById(R.id.editText2);
           editC = (EditText) findViewById(R.id.editText3);
          doubleA =Double.parseDouble(editA.getText().toString());
          doubleB =Double.parseDouble(editB.getText().toString());


              add = (Button) findViewById(R.id.add);
              subtract = (Button) findViewById(R.id.subtract);
              multiply = (Button) findViewById(R.id.multiply);
              devide = (Button) findViewById(R.id.devide);

               add.setOnClickListener(new View.OnClickListener() {
                   @Override
                   public void onClick(View v) {

                     doubleC = doubleA+doubleB;
                     String s = "" + doubleC;
                      editC.setText(s);


                   }
               });

               subtract.setOnClickListener(new View.OnClickListener() {
               @Override
               public void onClick(View v) {

                   doubleC = doubleA-doubleB;
                   String s = "" + doubleC;
                   editC.setText(s);


               }
           });

               multiply.setOnClickListener(new View.OnClickListener() {
               @Override
               public void onClick(View v) {

                   doubleC = doubleA*doubleB;
                   String s = "" + doubleC;
                   editC.setText(s);


               }
           });



           devide.setOnClickListener(new View.OnClickListener() {
               @Override
               public void onClick(View v) {

                   doubleC = doubleA/doubleB;
                   String s = "" + doubleC;
                   editC.setText(s);


               }
           });



       }



   }

******************activity_main.xml******************

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity"
      >


<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/idk"
    android:textSize="17sp"
    android:id="@+id/textView"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true" />

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:inputType="numberDecimal"
    android:ems="5"
    android:id="@+id/editText"
    android:hint="First number"
    android:layout_centerVertical="true"
    android:layout_alignLeft="@+id/textView"
    android:layout_alignStart="@+id/textView" />

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:inputType="numberDecimal"
    android:ems="5"
    android:id="@+id/editText2"
    android:hint="Second number"
    android:layout_centerVertical="true"
    android:layout_alignRight="@+id/textView"
    android:layout_alignEnd="@+id/textView" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Add"
    android:id="@+id/add"
    android:layout_alignParentBottom="true"
    android:layout_alignLeft="@+id/editText"
    android:layout_alignStart="@+id/editText"
    android:layout_marginBottom="166dp" />

<Button
    android:layout_width="100dp"
    android:layout_height="50dp"
    android:text="Subtract"
    android:id="@+id/subtract"
    android:layout_alignTop="@+id/multiply"
    android:layout_alignLeft="@+id/add"
    android:layout_alignStart="@+id/add" />

<Button
    android:layout_width="100dp"
    android:layout_height="50dp"
    android:text="Multiply"
    android:id="@+id/multiply"
    android:layout_marginTop="58dp"
    android:layout_below="@+id/devide"
    android:layout_alignRight="@+id/devide"
    android:layout_alignEnd="@+id/devide" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Devide"
    android:id="@+id/devide"
    android:layout_below="@+id/editText"
    android:layout_alignLeft="@+id/editText2"
    android:layout_alignStart="@+id/editText2" />

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:ems="20"
    android:id="@+id/editText3"
    android:layout_below="@+id/textView"
    android:hint="Results"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="62dp" />


           </RelativeLayout>

Answer 1

您已经为Something 类创建了构造函数

public Something(Activity a) {

       click();

}

而不是使用onCreate() 可能是错误的来源。

Something 派生自Activity，其中您必须 至少覆盖onCreate()，并在其中设置Activity 的View。您还没有这样做，而是为 Something 创建了一个构造函数，这也是不允许的。

解决问题的方法是将构造函数替换为onCreate()，并使用setContentView() 设置Activity 的View。此外，您不能使用

创建Activity 对象

new Something(this);