来自custum imageview的setText Textview

Question

我有一个自定义imageView的活动。在imageView中，我想从活动中调用一个方法，该方法需要setText Textview。

可能吗？

我已经完成了这些代码，但我遇到了一个错误。

我的名字是c：

package com.example.helloworld;

import android.os.Bundle;
import android.app.Activity;
import android.util.Log;

public class MainActivity extends Activity {

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


   pubic void myFunction(int score){
       ((TextView)findViewById(R.id.txtScore)).setText(score+"");
   }

 }

XML：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:orientation="vertical" >

   <TextView android:id="@+id/txtScore"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="This is a TextView" />

   <com.example.MyImageView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
       />
</LinearLayout>

MyImageViewClass：

public class MyImageViewClass extends ImageView {

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

      protected void onDraw(Canvas canvas) {
             ((MainActivity)context).myFunction(12);
       }

 }

当从imageViewو调用myFunction（）时会出现这样的错误：

 Caused by: android.view.InflateException: Binary XML file line #9: Binary XML file line #9: Error inflating class com.example.adisun.gamesss.ImageViews.GmaeMemClassicImageView
        at android.view.LayoutInflater.inflate(LayoutInflater.java:551)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:429)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:380)
        at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:287)
        at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139)
        at com.example.adisun.gamesss.activity.GameActivity.onCreate(GameActivity.java:19)
        at android.app.Activity.performCreate(Activity.java:6904)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3266)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 
        at android.app.ActivityThread.access$1100(ActivityThread.java:229) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:148) 
        at android.app.ActivityThread.main(ActivityThread.java:7331) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
     Caused by: android.view.InflateException: Binary XML file line #9: Error inflating class com.example.adisun.gamesss.ImageViews.GmaeMemClassicImageView
        at android.view.LayoutInflater.createView(LayoutInflater.java:657)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:776)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:716)
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:847)
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:810)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:527)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:429) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:380) 
        at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:287) 
        at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139) 
        at com.example.adisun.gamesss.activity.GameActivity.onCreate(GameActivity.java:19) 
        at android.app.Activity.performCreate(Activity.java:6904) 
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136) 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3266) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 
        at android.app.ActivityThread.access$1100(ActivityThread.java:229) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:148) 
        at android.app.ActivityThread.main(ActivityThread.java:7331) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Constructor.newInstance(Native Method)
        at android.view.LayoutInflater.createView(LayoutInflater.java:631)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:776) 
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:716) 
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:847) 
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:810) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:527) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:429) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:380) 
        at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:287) 
        at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139) 
        at com.example.adisun.gamesss.activity.GameActivity.onCreate(GameActivity.java:19) 
        at android.app.Activity.performCreate(Activity.java:6904) 
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136) 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3266) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 
        at android.app.ActivityThread.access$1100(ActivityThread.java:229) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:148) 
        at android.app.ActivityThread.main(ActivityThread.java:7331) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
        at com.example.adisun.gamesss.activity.GameActivity.setScore(GameActivity.java:38)
        at com.example.adisun.gamesss.ImageViews.GmaeMemClassicImageView.initialize(GmaeMemClassicImageView.java:75)

Answer 1

问题在这里((MainActivity)context).myFunction(12)在onDraw内被调用。这就是你获得NPE->的原因

引发者：java.lang.NullPointerException：尝试在空对象引用上调用虚方法'void android.widget.TextView.setText（java.lang.CharSequence）'

你不能从另一个观点的View访问onDraw，因为Activity的布局还没有膨胀。即使你可以，这也不是一种方式，因为每当onDraw被调用时，invalidate会多次被调用。

寻找一些优雅的方法来解决您的问题。你的问题非常不清楚，所以我不能提出任何建议。