java.lang.RuntimeException: Unable to start activity ComponentInfo{com.cwy/com.cwy.MainActivity}

03-19 06:20:21.947 2086-2086/com.cwy E/AndroidRuntime: FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.cwy/com.cwy.MainActivity}: android.view.InflateException: Binary XML file line #7: Error inflating class com.cwy.Tank
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
        at android.app.ActivityThread.access$600(ActivityThread.java:141)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:5041)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
        at dalvik.system.NativeStart.main(Native Method)
     Caused by: android.view.InflateException: Binary XML file line #7: Error inflating class com.cwy.Tank
        at android.view.LayoutInflater.createView(LayoutInflater.java:596)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:687)
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:746)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:352)
        at android.support.v7.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:469)
        at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140)
        at com.cwy.MainActivity.onCreate(MainActivity.java:11)
        at android.app.Activity.performCreate(Activity.java:5104)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
        at android.app.ActivityThread.access$600(ActivityThread.java:141) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:137) 
        at android.app.ActivityThread.main(ActivityThread.java:5041) 
        at java.lang.reflect.Method.invokeNative(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:511) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
        at dalvik.system.NativeStart.main(Native Method) 
     Caused by: java.lang.NoSuchMethodException:  [class android.content.Context, interface android.util.AttributeSet]
        at java.lang.Class.getConstructorOrMethod(Class.java:460)
        at java.lang.Class.getConstructor(Class.java:431)
        at android.view.LayoutInflater.createView(LayoutInflater.java:561)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:687) 
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:746) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:489) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:396) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:352) 
        at android.support.v7.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:469) 
        at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140) 
        at com.cwy.MainActivity.onCreate(MainActivity.java:11) 
        at android.app.Activity.performCreate(Activity.java:5104) 
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
        at android.app.ActivityThread.access$600(ActivityThread.java:141) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:137) 
        at android.app.ActivityThread.main(ActivityThread.java:5041) 
        at java.lang.reflect.Method.invokeNative(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:511) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
        at dalvik.system.NativeStart.main(Native Method) 

自定义控件时， 出现这个错误。

原因是少加了

    public Tank(Context context, AttributeSet attrs) {
        super(context, attrs);
    }