Android工作室在启动另一个活动时显示致命异常错误

Question

我在我的应用中创建了两个活动。 当我点击MainActivity中的一个按钮时，它显示致命异常错误。

MainActivity.java

  package com.example.ravi.testingstudio;

    import android.content.Intent;
    import android.os.Bundle;
    import android.support.v7.app.AppCompatActivity;
    import android.view.View;
    import android.widget.Button;

    import com.google.android.gms.ads.AdRequest;
    import com.google.android.gms.ads.AdView;
    import com.google.android.gms.ads.MobileAds;


    public class MainActivity extends AppCompatActivity {

    Button button;
    AdView adView;

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

        button = (Button)findViewById(R.id.button);
        MobileAds.initialize(this, "ca-app-pub-3940256099942544~3347511713");
        adView = (AdView)findViewById(R.id.adView);
        AdRequest adRequest = new AdRequest.Builder().addTestDevice(AdRequest.DEVICE_ID_EMULATOR).build();
        adView.loadAd(adRequest);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this, SecondActivity.class);
                startActivity(intent);
            }
        });



    }
}

`

activity_main.xml文件

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".SecondActivity">


    <TextView
        android:id="@+id/txt"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="Second Activity"
        android:textSize="25sp"
        app:layout_constraintTop_toTopOf="parent"
        tools:layout_editor_absoluteX="0dp"
        tools:ignore="MissingConstraints" />

    <Button
        android:id="@+id/btn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Go to First Activity"

        android:gravity="center"
        android:layout_marginBottom="@id/txt"/>

</android.support.constraint.ConstraintLayout>

SecondActivity.java文件

package com.example.ravi.testingstudio;

   import android.content.Intent;
   import android.os.Bundle;
   import android.support.v7.app.AppCompatActivity;
   import android.view.View;
   import android.widget.Button;

`public class SecondActivity extends AppCompatActivity {`

    Button btn;

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

        btn= (Button)findViewById(R.id.btn);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(SecondActivity.this, MainActivity.class);
                startActivity(intent);
            }
        });


    }
}

second_main.xml文件

      <android.support.constraint.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".SecondActivity">


    <TextView
        android:id="@+id/txt"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="Second Activity"
        android:textSize="25sp"
        app:layout_constraintTop_toTopOf="parent"
        tools:layout_editor_absoluteX="0dp"
        tools:ignore="MissingConstraints" />

    <Button
        android:id="@+id/btn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Go to First Activity"

        android:gravity="center"
        android:layout_marginBottom="@id/txt"/>

</android.support.constraint.ConstraintLayout>

错误消息显示 enter code here

`E/AndroidRuntime: FATAL EXCEPTION: main
 Process: com.example.ravi.testingstudio, PID: 4469
        java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ravi.testingstudio/com.example.ravi.testingstudio.SecondActivity}: android.view.InflateException: Binary XML file line #21: Can't convert value at index 6 to dimension: type=0x12
        at 
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
        at 
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at 
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6077)
        at java.lang.reflect.Method.invoke(Native Method)
        at

com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
         Caused by: android.view.InflateException: Binary XML file line #21: 
    Can't convert value at index 6 to dimension: type=0x12
         Caused by: java.lang.UnsupportedOperationException: Can't convert value at index 6 to dimension: type=0x12
            at android.content.res.TypedArray.getDimensionPixelSize(TypedArray.java:720)
            at android.view.ViewGroup$MarginLayoutParams.<init>(ViewGroup.java:7271)
            at android.support.constraint.ConstraintLayout$LayoutParams.<init>(ConstraintLayout.java:2590)
            at android.support.constraint.ConstraintLayout.generateLayoutParams(ConstraintLayout.java:1913)
            at android.support.constraint.ConstraintLayout.generateLayoutParams(ConstraintLayout.java:475)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:860)
            at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:821)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:518)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:426)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:377)
            at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:287)
            at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139)
            at com.example.ravi.testingstudio.SecondActivity.onCreate(SecondActivity.java:14)
            at android.app.Activity.performCreate(Activity.java:6664)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
            at android.app.ActivityThread.-wrap12(ActivityThread.java)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:154)
            at android.app.ActivityThread.main(ActivityThread.java:6077)
            at java.lang.reflect.Method.invoke(Native Method)
            at     
and com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
enter code here
        `