android studio ..代码没有错误但有异常

Question

我在 Android Studio 中编写代码，代码中没有错误，但是当我运行它时它不起作用，并在我运行时显示“致命异常”错误。 这是我的代码:

在 MainActivity.java 中

package com.example.hayfa.sharingwithmultimedia;

import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.provider.MediaStore;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ImageView;

import java.io.File;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    Uri uri;
    ImageView mImageView = (ImageView) findViewById(R.id.imageView);
    static final int REQUEST_IMAGE_CAPTURE = 1;

    public void dispatchTakePictureIntent(View view){
        Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        if(takePictureIntent.resolveActivity(getPackageManager())!=null){
            startActivityForResult(takePictureIntent, REQUEST_IMAGE_CAPTURE);
        }

    }

    public void onActivityResult(int requestCode, int resultCode, Intent data) {

        if (requestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK) {
            Bundle extras = data.getExtras();
            Bitmap imageBitmap = (Bitmap) extras.get("data");
            mImageView.setImageBitmap(imageBitmap);
        }
        File image=new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), "picture.jpg");
        uri= Uri.fromFile(image);
        data.putExtra(MediaStore.EXTRA_OUTPUT, uri);
    }

    public void sendImage(View view){
        Intent intent = new Intent();
        intent.setAction(Intent.ACTION_SEND);
        intent.putExtra(Intent.EXTRA_STREAM, "This is my text to send");
        intent.putExtra(Intent.EXTRA_STREAM, uri);

        intent.putExtra(android.content.Intent.EXTRA_SUBJECT, "From my app");
        intent.setType("image/jpeg");
        startActivity(Intent.createChooser(intent,"Share image to "));
    }
}

list

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.hayfa.sharingwithmultimedia">

    <uses-feature android:name="android.hardware.camera"
        android:required="true"/>

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

contentmain.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.example.hayfa.sharingwithmultimedia.MainActivity"
    tools:showIn="@layout/activity_main">

    <ImageView
        android:layout_width="300dip"
        android:layout_height="300dip"
        android:id="@+id/imageView"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=" TAKE PICTURE"
        android:onClick="dispatchTakePictureIntent"
        android:id="@+id/button"
        android:layout_below="@+id/imageView"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="41dp" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="SHARE PICTURE"
        android:onClick="sendImage"
        android:id="@+id/button2"
        android:layout_below="@+id/button"
        android:layout_alignLeft="@+id/button"
        android:layout_alignStart="@+id/button" />
</RelativeLayout>

Answer 1

在 onCreate() 中调用 setContentView(...) 之前，您不能使用 findViewById。

首先只声明你的ImageView

private ImageView mImageView;

然后在onCreate()

中赋值

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mImageView = (ImageView) findViewById(R.id.imageView);
}