1.先讲一个错误：

image.png

上网查了一下：
@dimen/activity_vertical_margin这个的意思就是在values文件夹下面的dimens文件里面有一个name叫做activity_vertical_margin的项，这个项里面值就是你android:paddingBottom的值，而我这里无法识别,说明在values文件里面缺少dimens文件,或者dimens文件里面缺少对应的项;
果然添加了这个文件以及相关代码之后,不再报错:

image.png

dimens.xml：

<?xml version="1.0" encoding="utf-8"?>


    <resources>
        <!-- Example customization of dimensions originally defined in res/values/dimens.xml
             (such as screen margins) for screens with more than 820dp of available width. This
             would include 7" and 10" devices in landscape (~960dp and ~1280dp respectively). -->
        <dimen name="activity_horizontal_margin">64dp</dimen>
    <dimen name="activity_vertical_margin">64dp</dimen>
    </resources>

activity_main.xml文件：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context="com.example.my_telephone.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />

    <Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="click me"/>
</LinearLayout>

申请权限在清单文件中：

AndroidMainifest.xml文件：(清单文件)
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.my_telephone">
    <uses-permission android:name="android.permission.CALL_PHONE" />
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">

            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

MainActivity.java文件
package com.example.my_telephone;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button btn = (Button)findViewById(R.id.btn);//获取按钮控件对象

        btn.setOnClickListener(new View.OnClickListener() {//设置监听器
            @Override
            public void onClick(View v) {
                Intent callIntent = new Intent(Intent.ACTION_CALL); //use ACTION_CALL class
                callIntent.setData(Uri.parse("tel:0800000000"));    //this is the phone number calling
                //check permission
                //If the device is running Android 6.0 (API level 23) and the app's targetSdkVersion is 23 or higher,
                //the system asks the user to grant approval.
                if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CALL_PHONE) != PackageManager.PERMISSION_GRANTED) {
                    //request permission from user if the app hasn't got the required permission
                    ActivityCompat.requestPermissions(MainActivity.this,
                            new String[]{Manifest.permission.CALL_PHONE},   //request specific permission from user
                            10);
                    return;
                }else {     //have got permission
                    try{
                        startActivity(callIntent);  //call activity and make phone call
                    }
                    catch (android.content.ActivityNotFoundException ex){
                        Toast.makeText(getApplicationContext(),"yourActivity is not founded", Toast.LENGTH_SHORT).show();
                    }
                }
            }
        });

    }
}