android - CameraX PreviewView 到位图而不是文件

问题描述

我知道还有其他问题被回答了很多次，我试图找到答案，但我最不能理解它。我想让相机拍照，但不是制作物理图像文件，而是直接将其制作为位图并从不同的活动中将其显示在 ImageView 中，但是我不断得到Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference，这是因为这viewFinder.bitmap是一个空值，并决定制作一个单独的函数getBitmap(): Bitmap?。我不知道它要我诚实地做什么或由此产生的任何线索，我想做的就是将照片作为位图直接放到 ImageView 上。先感谢您。

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.camerax5, PID: 5472
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.camerax5/com.example.camerax5.VirtualPreview}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3141)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3284)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1972)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7179)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:975)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
        at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:164)
        at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:157)
        at android.content.Context.obtainStyledAttributes(Context.java:677)
        at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:842)
        at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:809)
        at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:633)
        at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:259)
        at com.example.camerax5.MainActivity.getBitmap(MainActivity.kt:118)
        at com.example.camerax5.VirtualPreview.onCreate(VirtualPreview.kt:19)
        at android.app.Activity.performCreate(Activity.java:7335)
        at android.app.Activity.performCreate(Activity.java:7326)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1275)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3121)

所以问题就出现在这一行：

viewFinder = findViewById(R.id.previewView)

这是我试图做的完整代码：

MainActivity.kt 和 MainActivity 代码下面是另一个具有另一个活动的类，用于在 ImageView 中显示位图，我添加这种方式是因为我不想将它们分开并使它们混淆：

class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        viewFinder = findViewById(R.id.previewView)

        //Permissions
        if (allPermissions()) {
            startCamera()
        } else {
            ActivityCompat.requestPermissions(this, REQUIRED_PERMISSIONS, REQUEST_CODE_PERMISSIONS)
        }

        //Capture button
        val captureBtn: Button = findViewById(R.id.captureButton)
        captureBtn.setOnClickListener {
            takePhoto()
        }

        outputDirectory = outputDirectoryFolder()

        cameraExecutor = Executors.newSingleThreadExecutor()
    }

private fun takePhoto() {
        Toast.makeText(baseContext, "Processing ..", Toast.LENGTH_SHORT).show()

        //Directly to open the new Activity
        val intent = Intent(this, VirtualPreview::class.java)
        startActivity(intent)
    }

    fun getBitmap(): Bitmap? {
        //Preview to Bitmap
        viewFinder = findViewById(R.id.previewView)
        val source = viewFinder.bitmap
        val newWidth = 200
        val newHeight = 200

        val bitmapWidth = source?.width
        val bitmapHeight = source?.height

        //Matrix
        val matrix = Matrix()
        val scaleWidth = newWidth.toFloat() / bitmapWidth!!
        val scaleHeight = newHeight.toFloat() / bitmapHeight!!
        matrix.postScale(scaleWidth, scaleHeight)

        return Bitmap.createBitmap(source, 0, 0, newWidth, newHeight, matrix, true)
    }
}

class VirtualPreview : AppCompatActivity() {
    private lateinit var acceptButton: Button
    private lateinit var denyButton: Button
    private lateinit var imageView: ImageView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_virtual_preview)

        val bitmapPreview = MainActivity().getBitmap()

        val drawableBitmap = BitmapDrawable(resources, bitmapPreview)
        imageView = findViewById(R.id.imagePreview)
        imageView.setImageDrawable(drawableBitmap)

        acceptButton = findViewById(R.id.acceptButton)
        acceptButton.setOnClickListener {

        }

        denyButton = findViewById(R.id.denyButton)
        denyButton.setOnClickListener {
            //delete the matrix and returns to the main activity
            finish()
        }
    }
}

标签： androidkotlin

android - CameraX PreviewView 到位图而不是文件

问题描述

解决方案

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