Android 活动和片段的上下文不同?
我正在尝试集成一些代码,其中一行是:Android 活动和片段的上下文不同?,android,android-fragments,Android,Android Fragments,我正在尝试集成一些代码,其中一行是: mPreview = new CameraPreview(this, mCamera, previewCb, autoFocusCB); 当我在活动中使用它时,没有错误。当我将其放入片段中时,我得到以下错误: 预期:android.content.context 实际:此(com.xxx.ScanFragment) 这是CameraPreview方法 public CameraPreview(Context
mPreview = new CameraPreview(this, mCamera, previewCb, autoFocusCB);
当我在活动中使用它时,没有错误。当我将其放入片段中时,我得到以下错误:
预期:android.content.context
实际:此(com.xxx.ScanFragment)
这是CameraPreview方法
public CameraPreview(Context context, Camera camera,
PreviewCallback previewCb,
AutoFocusCallback autoFocusCb)
正如我所说,在活动文件中没有错误,所以我假设问题在于活动和片段之间的“上下文”是什么
import android.content.Intent;
import android.content.pm.ActivityInfo;
import android.hardware.Camera;
import android.os.Bundle;
import android.os.Handler;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.TextView;
import com.parse.ParseUser;
import net.sourceforge.zbar.Config;
import net.sourceforge.zbar.Image;
import net.sourceforge.zbar.ImageScanner;
import net.sourceforge.zbar.Symbol;
import net.sourceforge.zbar.SymbolSet;
/**
* Created by Jakub on 7/23/2014.
*/
public class Pay extends Fragment {
private Button scanBtn;
private TextView formatTxt, contentTxt;
private Camera mCamera;
private CameraPreview mPreview;
private Handler autoFocusHandler;
TextView scanText;
Button scanButton;
ImageScanner scanner;
private boolean barcodeScanned = false;
private boolean previewing = true;
static {
System.loadLibrary("iconv");
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_pay, container, false);
return rootView;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
autoFocusHandler = new Handler();
mCamera = getCameraInstance();
/* Instance barcode scanner */
scanner = new ImageScanner();
scanner.setConfig(0, Config.X_DENSITY, 3);
scanner.setConfig(0, Config.Y_DENSITY, 3);
mPreview = new CameraPreview(getActivity(), mCamera, previewCb, autoFocusCB);
FrameLayout preview = (FrameLayout)getActivity().findViewById(R.id.cameraPreview);
Log.d(Payspot.TAG,"This is the string:" + preview.toString());
preview.addView(mPreview);
scanText = (TextView)getActivity().findViewById(R.id.scanText);
scanButton = (Button)getActivity().findViewById(R.id.ScanButton);
scanButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
if (barcodeScanned) {
barcodeScanned = false;
scanText.setText("Scanning...");
mCamera.setPreviewCallback(previewCb);
mCamera.startPreview();
previewing = true;
mCamera.autoFocus(autoFocusCB);
}
}
});
}
public void onPause() {
super.onPause();
releaseCamera();
}
/** A safe way to get an instance of the Camera object. */
public static Camera getCameraInstance(){
Camera c = null;
try {
c = Camera.open();
} catch (Exception e){
}
return c;
}
private void releaseCamera() {
if (mCamera != null) {
previewing = false;
mCamera.setPreviewCallback(null);
mCamera.release();
mCamera = null;
}
}
private Runnable doAutoFocus = new Runnable() {
public void run() {
if (previewing)
mCamera.autoFocus(autoFocusCB);
}
};
Camera.PreviewCallback previewCb = new Camera.PreviewCallback() {
public void onPreviewFrame(byte[] data, Camera camera) {
Camera.Parameters parameters = camera.getParameters();
Camera.Size size = parameters.getPreviewSize();
Image barcode = new Image(size.width, size.height, "Y800");
barcode.setData(data);
int result = scanner.scanImage(barcode);
if (result != 0) {
previewing = false;
mCamera.setPreviewCallback(null);
mCamera.stopPreview();
SymbolSet syms = scanner.getResults();
for (Symbol sym : syms) {
scanText.setText("barcode result " + sym.getData());
barcodeScanned = true;
}
}
}
};
// Mimic continuous auto-focusing
Camera.AutoFocusCallback autoFocusCB = new Camera.AutoFocusCallback() {
public void onAutoFocus(boolean success, Camera camera) {
autoFocusHandler.postDelayed(doAutoFocus, 1000);
}
};
}
在片段中,必须调用
getActivity()
方法才能获取上下文。因为片段必须与活动关联,并且具有活动上下文(活动扩展上下文)。活动扩展上下文,但片段没有。这就是为什么可以为上下文参数传递它This
。因此,错误消息将您的ScanFragment视为上下文的参数,但该参数不起作用。每个片段都与活动的片段相关联。您可以使用getActivity()
或getActivity().getApplicationContext()
接收在这些情况下使用的有效上下文
您的新代码将是:
mPreview=new-CameraPreview(getActivity()、mCamera、previewCb、autoFocusCB)代码>是否尝试从片段中传递活动上下文?在你的片段中使用getActivity()方法?那么我会用getActivity()替换它吗?或者我到底把它叫什么?我用getActivity()替换了它,现在得到了一个NullPointerExceptions。我要用getActivity()替换它吗?或者我到底把它叫什么?我用getActivity()替换了它,现在得到了一个NullPointerExceptions。我要用getActivity()替换它吗?或者我到底把它叫什么?我用getActivity()替换了它,现在得到一个nullPointerExceptionHmmmm,你是说getActivity()返回null?或者mPreview为空?我在代码中添加了。看起来getActivity()调用下面一行中的“preview”实际上为null,这可能是一个不相关的问题?不过,这在Activity类中不是问题,现在在fragmentpreview.addView(mPreview)中;虽然错误也出现在我尝试转换preview.toString之前的调试行中(可能是因为它为null),但这与原始问题无关。通常,对于碎片,使用提供的充气器在onCreateView()中执行视图操作。膨胀片段的布局以获得视图,并使用该视图使用findViewById()。