Question

我知道有许多问题与许多问题相同，但是许多读过的人都不等于我的或曾为我工作过帮助，所以这需要你的帮助。我正在使用NavigationDrawer处理应用程序，我需要在蓝牙单元上打开和关闭图像。我用＆＃34;分别制作了另一个代码。空活动＆＃34;如果我工作，但在navigariondrawe，我需要它工作，但它不起作用，我已经尝试了很多东西，但我希望你能帮助我。

＆＃13;

FATAL EXCEPTION: main
Process: com.example.lab02pc19.myapplication2, PID: 5146
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.lab02pc19.myapplication2/com.example.lab02pc19.myapplication2.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2426)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference
at com.example.lab02pc19.myapplication2.MainActivity.setImagenBluetooth(MainActivity.java:69)
at com.example.lab02pc19.myapplication2.MainActivity.onCreate(MainActivity.java:36)
at android.app.Activity.performCreate(Activity.java:6245)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5443) 
at java.lang.reflect.Method.invoke(Native Method)

＆＃13;

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.lab02pc19.myapplication2">
    <uses-permission android:name="android.permission.BLUETOOTH"/>
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>

    <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>

＆＃13;

package com.example.lab02pc19.myapplication2;

import android.bluetooth.BluetoothAdapter;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener, FragmentBlue.OnFragmentInteractionListener {
     ImageView miimagen;
    BluetoothAdapter adaptador_bluetooth;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        miimagen= (ImageView)findViewById(R.id.ivw);
        adaptador_bluetooth= BluetoothAdapter.getDefaultAdapter();
        if(adaptador_bluetooth==null)
        {
         miimagen.setVisibility(View.GONE);
        }
        else
        {
         setImagenBluetooth(adaptador_bluetooth.isEnabled());
        }



        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
    }
    public void clickImagen(View view)
    {
        switch (view.getId())
        {

            case R.id.ivw:
                setEstadoBluetooth();
                break;

        }

    }
    public void miimagen()
    {
        setEstadoBluetooth();
    }

    public void setImagenBluetooth(boolean valor)
    {
     if(valor)miimagen.setImageResource(R.drawable.ic_action_bluetooth);

    }

    public void setEstadoBluetooth()
    {
        if(adaptador_bluetooth.isEnabled())
        {
         setImagenBluetooth(false);
            adaptador_bluetooth.disable();
        }
        else
        {
          setImagenBluetooth(true);
            adaptador_bluetooth.enable();
        }
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.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);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {

        int id = item.getItemId();
        boolean FragmenTransaction= false;
        Fragment fragment = null;

        if (id == R.id.nav_camera) {
            fragment = new FragmentBlue();
            FragmenTransaction= true;

        } else if (id == R.id.nav_gallery) {

        } else if (id == R.id.nav_slideshow) {

        } else if (id == R.id.nav_manage) {

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

        if(FragmenTransaction)
        {
         getSupportFragmentManager().beginTransaction().replace(R.id.content_main,fragment).commit();
            item.setChecked(true);
            getSupportActionBar().setTitle(item.getTitle());
        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    @Override
    public void onFragmentInteraction(Uri uri) {

    }
}

＆＃13;

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.lab02pc19.myapplication2.FragmentBlue">

    <!-- TODO: Update blank fragment layout -->


    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/ivw"
        android:layout_gravity="left|top"
        android:background="@drawable/ic_action_bluetooth"
        android:clickable="true"
        android:onClick="clickImagen"
        android:contentDescription="@string/imagen" />
</FrameLayout>

＆＃13;

Answer 1

正如我想的那样（信息不够），您希望在活动中创建一个片段，并进一步使用ImageView进行一些操作。但你没有创建片段并尝试在其他布局中通过id找到ImageView - 因此，图像视图在这里不存在，接下来你尝试调用null对象的函数，最后有一个NPE和崩溃。您需要在Android中阅读有关片段的教程：https://developer.android.com/training/basics/fragments/index.html

Answer 2

您正在尝试访问活动类中片段的图像视图，这是无法提供空点异常的原因。在设置contentView之后，你可以在onActivityCreated覆盖方法中的图片视图中的setImage中设置setImage。如果只想从活动中设置图像，则可以在片段中创建公共方法，并从活动中调用方法。

java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.lab02pc19

2 个答案: