Question

我尝试使用此链接中的基本Camera2在camera2预览上绘制一个矩形： https://github.com/googlesamples/android-Camera2Basic

我在论坛上关注了这个问题的答案：

android Camera2 API + TextureView overlay for drawing on camera preview

但是我无法让它发挥作用。如果你能帮助我弄清楚如何解决我的问题，我将非常感激。以下是用于绘制矩形的类： Rectangle.java

package com.example.android.camera2basic;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.view.View;

public class Rectangle extends View {
Paint paint = new Paint();

public Rectangle(Context context) {
    super(context);
}


@Override
public void onDraw(Canvas canvas) {
    paint.setColor(Color.GREEN);
    paint.setStyle(Paint.Style.FILL);
    Rect rect = new Rect(20, 56, 200, 112);
    canvas.drawRect(rect, paint );
}
}

相机的xml文件 activity_camera.xml ：

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

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#000"
tools:context="com.example.android.camera2basic.CameraActivity">

<LinearLayout
android:id="@+id/surface"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" />

</FrameLayout>

这是我在类中使用的方法，我将矩形添加到相机预览 Camera2BasicFragment.java ：

  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.fragment_camera2_basic, container, 
    false);
    LinearLayout linearLayout = (LinearLayout) 
    view.findViewById(R.id.surface);
    linearLayout.addView(new Rectangle(getActivity()));
    return view;
    }

并且最终在应用程序在启动时崩溃后出现错误：

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.camera2basic/com.example.android.camera2basic.CameraActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.LinearLayout.addView(android.view.View)' on a null object reference
                                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2793)
                                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2864)
                                                                                  at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1567)
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:105)
                                                                                  at android.os.Looper.loop(Looper.java:156)
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:6523)
                                                                                  at java.lang.reflect.Method.invoke(Native Method)
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:941)
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:831)
                                                                               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.LinearLayout.addView(android.view.View)' on a null object reference
                                                                                  at com.example.android.camera2basic.Camera2BasicFragment.onCreateView(Camera2BasicFragment.java:431)
                                                                                  at android.app.Fragment.performCreateView(Fragment.java:2361)
                                                                                  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1000)
                                                                                  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1178)
                                                                                  at android.app.BackStackRecord.run(BackStackRecord.java:815)
                                                                                  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1585)
                                                                                  at android.app.FragmentController.execPendingActions(FragmentController.java:371)
                                                                                  at android.app.Activity.performStart(Activity.java:6929)
                                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2756)
                                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2864) 
                                                                                  at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1567) 
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:105) 
                                                                                  at android.os.Looper.loop(Looper.java:156) 
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:6523) 
                                                                                  at java.lang.reflect.Method.invoke(Native Method)

Answer 1

感谢@ cricket_007的评论，我想到了我的错误。我在错误的xml文件中初始化LinearLayout。它应该在fragment_camera2_basic.xml

中

另外，为了设置在相机预览上获取矩形，您应该在此代码之后添加它：

<com.example.android.camera2basic.AutoFitTextureView
    android:id="@+id/texture"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentStart="true"
    android:layout_alignParentTop="true" />

所以最终的xml文件看起来像这样 fragment_camera2_basic.xml：

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


    <com.example.android.camera2basic.AutoFitTextureView
        android:id="@+id/texture"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true" />
    <LinearLayout
        android:id="@+id/surface"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical" />

    <FrameLayout
        android:id="@+id/control"
        android:layout_width="match_parent"
        android:layout_height="112dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentStart="true"
        android:background="@color/control_background">

        <Button
            android:id="@+id/picture"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text="@string/picture" />

        <ImageButton
            android:id="@+id/info"
            android:contentDescription="@string/description_info"
            style="@android:style/Widget.Material.Light.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical|right"
            android:padding="20dp"
            android:src="@drawable/ic_action_info" />

    </FrameLayout>

</RelativeLayout>

P.S：要设法使矩形未填充，请在 Rectangle.class 中使用它：paint.setStyle(Paint.Style.STROKE);

在camera2上绘制矩形预览android

1 个答案: