Question

我一直在从youtube上学习一下Android自定义视图和所有内容。在我尝试进行Surface View时（相当简单，如this视频中所述）。

我做的事情几乎与视频中显示的内容同步。

我怎么在surfaceHolder.getSurface（）中收到空指针异常。

这是我的整个代码：

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.SurfaceHolder;
import android.view.SurfaceView;


public class MainActivity extends AppCompatActivity {

    Ui ui;
    Bitmap ball;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.activity_main);
        ui = new Ui(this);
        ball = BitmapFactory.decodeResource(getResources(), R.drawable.ball);
        setContentView(ui);
    }

    @Override
    protected void onResume() {
        super.onResume();
        ui.resume();
    }

    @Override
    protected void onPause() {
        super.onPause();
        ui.pause();
    }

    @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);
    }


    public class Ui extends SurfaceView implements Runnable {

        private Thread thread;
        private SurfaceHolder surfaceHolder;
        boolean ok = false;


        public Ui(Context context) {
            super(context);
            thread = null;
            surfaceHolder = getHolder();
        }

        @Override
        public void run() {
            while (ok) {
                if (!surfaceHolder.getSurface().isValid()) {
                    continue;
                }
                Canvas canvas = surfaceHolder.lockCanvas();
                canvas.drawARGB(200, 150, 130, 120);
                canvas.drawBitmap(ball, 0, 0, null);
                surfaceHolder.unlockCanvasAndPost(canvas);
            }
        }

        public void pause() {
            ok = false;
            while (true) {
                try {
                    thread.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                break;
            }
            thread = null;
        }

        public void resume() {
            ok = true;
            thread = new Thread(this);
            thread.run();
        }

    }
}

这部分代码：

指向我做错的一些指针会有所帮助！

@Override
            public void run() {
                while (ok) {
                    if (!surfaceHolder.getSurface().isValid()) {
                        continue;
                    }
                    Canvas canvas = surfaceHolder.lockCanvas();
                    canvas.drawARGB(200, 150, 130, 120);
                    canvas.drawBitmap(ball, 0, 0, null);
                    surfaceHolder.unlockCanvasAndPost(canvas);
                }
            }

问题出现在这一行：

if (!surfaceHolder.getSurface().isValid())

总是返回false，代码的后半部分永远不会被执行。

Logcat：

06-25 15:23:46.211    2012-2012/com.pchakraverti.canvasapp D/AndroidRuntime﹕ Shutting down VM
06-25 15:23:46.211    2012-2012/com.pchakraverti.canvasapp W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xa62f8288)
06-25 15:23:46.211    2012-2012/com.pchakraverti.canvasapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to resume activity {com.pchakraverti.canvasapp/com.pchakraverti.canvasapp.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2575)
            at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2603)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2089)
            at android.app.ActivityThread.access$600(ActivityThread.java:130)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4745)
            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:786)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.pchakraverti.canvasapp.Ui.run(Ui.java:44)
            at java.lang.Thread.run(Thread.java:856)
            at com.pchakraverti.canvasapp.Ui.resume(Ui.java:66)
            at com.pchakraverti.canvasapp.MainActivity.onPostResume(MainActivity.java:24)
            at android.app.Activity.performResume(Activity.java:5095)
            at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2565)
            at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2603)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2089)
            at android.app.ActivityThread.access$600(ActivityThread.java:130)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4745)
            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:786)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)
06-25 15:23:46.227    2012-2015/com.pchakraverti.canvasapp D/dalvikvm﹕ GC_CONCURRENT freed 208K, 3% free 10919K/11207K, paused 12ms+0ms, total 15ms
06-25 15:25:15.043    2067-2067/com.pchakraverti.canvasapp D/dalvikvm﹕ Late-enabling CheckJNI
06-25 15:25:15.091    2067-2070/com.pchakraverti.canvasapp D/dalvikvm﹕ GC_CONCURRENT freed 98K, 3% free 11074K/11335K, paused 11ms+0ms, total 23ms
06-25 15:25:15.095    2067-2067/com.pchakraverti.canvasapp D/dalvikvm﹕ GC_FOR_ALLOC freed <1K, 3% free 11073K/11335K, paused 4ms, total 4ms
06-25 15:25:15.131    2067-2067/com.pchakraverti.canvasapp I/dalvikvm-heap﹕ Grow heap (frag case) to 11.887MB for 1048588-byte allocation
06-25 15:25:15.155    2067-2070/com.pchakraverti.canvasapp D/dalvikvm﹕ GC_CONCURRENT freed 0K, 3% free 12097K/12423K, paused 15ms+0ms, total 22ms
06-25 15:25:15.155    2067-2067/com.pchakraverti.canvasapp D/dalvikvm﹕ WAIT_FOR_CONCURRENT_GC blocked 0ms
06-25 15:25:15.163    2067-2067/com.pchakraverti.canvasapp I/dalvikvm﹕ Could not find method android.view.ViewGroup.onRtlPropertiesChanged, referenced from method android.support.v7.widget.Toolbar.onRtlPropertiesChanged
06-25 15:25:15.163    2067-2067/com.pchakraverti.canvasapp W/dalvikvm﹕ VFY: unable to resolve virtual method 13337: Landroid/view/ViewGroup;.onRtlPropertiesChanged (I)V
06-25 15:25:15.163    2067-2067/com.pchakraverti.canvasapp D/dalvikvm﹕ VFY: replacing opcode 0x6f at 0x0007
06-25 15:25:15.163    2067-2067/com.pchakraverti.canvasapp I/dalvikvm﹕ Could not find method android.content.res.TypedArray.getChangingConfigurations, referenced from method android.support.v7.internal.widget.TintTypedArray.getChangingConfigurations
06-25 15:25:15.163    2067-2067/com.pchakraverti.canvasapp W/dalvikvm﹕ VFY: unable to resolve virtual method 408: Landroid/content/res/TypedArray;.getChangingConfigurations ()I
06-25 15:25:15.163    2067-2067/com.pchakraverti.canvasapp D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x0002
06-25 15:25:15.167    2067-2067/com.pchakraverti.canvasapp I/dalvikvm﹕ Could not find method android.content.res.TypedArray.getType, referenced from method android.support.v7.internal.widget.TintTypedArray.getType
06-25 15:25:15.167    2067-2067/com.pchakraverti.canvasapp W/dalvikvm﹕ VFY: unable to resolve virtual method 430: Landroid/content/res/TypedArray;.getType (I)I
06-25 15:25:15.167    2067-2067/com.pchakraverti.canvasapp D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x0002
06-25 15:25:15.171    2067-2067/com.pchakraverti.canvasapp D/AndroidRuntime﹕ Shutting down VM
06-25 15:25:15.171    2067-2067/com.pchakraverti.canvasapp W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xa62f8288)
06-25 15:25:15.171    2067-2067/com.pchakraverti.canvasapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to resume activity {com.pchakraverti.canvasapp/com.pchakraverti.canvasapp.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2575)
            at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2603)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2089)
            at android.app.ActivityThread.access$600(ActivityThread.java:130)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4745)
            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:786)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.pchakraverti.canvasapp.Ui.run(Ui.java:45)
            at java.lang.Thread.run(Thread.java:856)
            at com.pchakraverti.canvasapp.Ui.resume(Ui.java:66)
            at com.pchakraverti.canvasapp.MainActivity.onPostResume(MainActivity.java:24)
            at android.app.Activity.performResume(Activity.java:5095)
            at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2565)
            at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2603)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2089)
            at android.app.ActivityThread.access$600(ActivityThread.java:130)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4745)
            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:786)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
            at dalvik.system.NativeStart.main(Native Method)
06-25 15:26:56.039    2120-2125/com.pchakraverti.canvasapp I/dalvikvm﹕ threadid=3: reacting to signal 3

Answer 1

请你也看看我自己发的这个问题，实际上，它非常相似：
View.SurfaceView, why its member, mSurfaceHolder, returns null from getSurface()?
我还在android sdk 22中阅读了SurfaceView.java的源代码，但我注意到成员SurfaceView.mSurfaceHolder.getSurface（）总是返回null。这让我感到震惊！

Answer 2

SurfaceView有两个部分，Surface和View。 Surface是由窗口管理器异步创建的，在它准备好之前你不能对它做任何事情。您必须处理SurfaceHolder.Callback方法以了解何时创建和销毁Surface。

SurfaceView生命周期与Activity生命周期没有锁定步骤，所以你必须要小心分配资源（如Camera）和启动/停止线程。可以在图形架构文档的this appendix中找到对该主题的讨论。可以在Grafika中找到各种示例。

请确保SurfaceView是您真正想要的。如果你想要一个custom View，你应该使用View而不是SurfaceView。

Android SurfaceHolder.getSurface导致空指针异常

2 个答案: