下载管理器应用程序下降

Question

我有一个问题。这段代码有什么问题？我点击下载按钮应用程序下降。我不知道我是否按照这里的说明做了：https://www.youtube.com/watch?v=pGlqHeB5hdk&index=76&list=FLGkGbI5dUEjLideBS_TOq-w

package downloader.download.downloader;
import android.app.DownloadManager;
import android.net.Uri;
import android.os.Environment;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends ActionBarActivity {
    Button button;
    EditText editText;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final Button button = (Button) findViewById(R.id.button);
        final EditText editText = (EditText) findViewById(R.id.editText);
        editText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            }
            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                button.setEnabled(!editText.getText().toString().trim().isEmpty());
            }
            @Override
            public void afterTextChanged(Editable s) {
            }
        });

    }

    public void download(View v)
    {
        DownloadManager.Request request = new DownloadManager.Request(Uri.parse(editText.getText().toString()));
request.setTitle("Downloader");
request.setDescription("Downloanding file!");
request.allowScanningByMediaScanner();
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_ONLY_COMPLETION);
  request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "Download file");
    }




    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.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);
    }
}

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/editText"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:hint="Link" />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Download"
        android:id="@+id/button"
        android:layout_below="@+id/editText"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignRight="@+id/editText"
        android:layout_alignEnd="@+id/editText"
        android:enabled="false"
        android:onClick="download" />
</RelativeLayout>

安卓清单

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="downloader.download.downloader" >
<uses-permission android:name="android.permission.INTERNET"/>
   <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
   <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>


    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

编辑：日志

03-08 17:51:06.055  14101-14101/downloader.download.downloader D/dalvikvm﹕ Late-enabling CheckJNI
03-08 17:51:06.565  14101-14101/downloader.download.downloader I/dalvikvm﹕ Could not find method android.view.ViewGroup.onNestedScrollAccepted, referenced from method android.support.v7.internal.widget.ActionBarOverlayLayout.onNestedScrollAccepted
03-08 17:51:06.565  14101-14101/downloader.download.downloader W/dalvikvm﹕ VFY: unable to resolve virtual method 11351: Landroid/view/ViewGroup;.onNestedScrollAccepted (Landroid/view/View;Landroid/view/View;I)V
03-08 17:51:06.565  14101-14101/downloader.download.downloader D/dalvikvm﹕ VFY: replacing opcode 0x6f at 0x0000
03-08 17:51:06.565  14101-14101/downloader.download.downloader I/dalvikvm﹕ Could not find method android.view.ViewGroup.onStopNestedScroll, referenced from method android.support.v7.internal.widget.ActionBarOverlayLayout.onStopNestedScroll
03-08 17:51:06.565  14101-14101/downloader.download.downloader W/dalvikvm﹕ VFY: unable to resolve virtual method 11357: Landroid/view/ViewGroup;.onStopNestedScroll (Landroid/view/View;)V
03-08 17:51:06.565  14101-14101/downloader.download.downloader D/dalvikvm﹕ VFY: replacing opcode 0x6f at 0x0000
03-08 17:51:06.565  14101-14101/downloader.download.downloader I/dalvikvm﹕ Could not find method android.support.v7.internal.widget.ActionBarOverlayLayout.stopNestedScroll, referenced from method android.support.v7.internal.widget.ActionBarOverlayLayout.setHideOnContentScrollEnabled
03-08 17:51:06.565  14101-14101/downloader.download.downloader W/dalvikvm﹕ VFY: unable to resolve virtual method 9045: Landroid/support/v7/internal/widget/ActionBarOverlayLayout;.stopNestedScroll ()V
03-08 17:51:06.565  14101-14101/downloader.download.downloader D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x000e
03-08 17:51:06.615  14101-14101/downloader.download.downloader I/dalvikvm﹕ Could not find method android.view.ViewGroup.onRtlPropertiesChanged, referenced from method android.support.v7.widget.Toolbar.onRtlPropertiesChanged
03-08 17:51:06.615  14101-14101/downloader.download.downloader W/dalvikvm﹕ VFY: unable to resolve virtual method 11354: Landroid/view/ViewGroup;.onRtlPropertiesChanged (I)V
03-08 17:51:06.615  14101-14101/downloader.download.downloader D/dalvikvm﹕ VFY: replacing opcode 0x6f at 0x0007
03-08 17:51:06.625  14101-14101/downloader.download.downloader I/dalvikvm﹕ Could not find method android.content.res.TypedArray.getChangingConfigurations, referenced from method android.support.v7.internal.widget.TintTypedArray.getChangingConfigurations
03-08 17:51:06.625  14101-14101/downloader.download.downloader W/dalvikvm﹕ VFY: unable to resolve virtual method 370: Landroid/content/res/TypedArray;.getChangingConfigurations ()I
03-08 17:51:06.625  14101-14101/downloader.download.downloader D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x0002
03-08 17:51:06.625  14101-14101/downloader.download.downloader I/dalvikvm﹕ Could not find method android.content.res.TypedArray.getType, referenced from method android.support.v7.internal.widget.TintTypedArray.getType
03-08 17:51:06.625  14101-14101/downloader.download.downloader W/dalvikvm﹕ VFY: unable to resolve virtual method 392: Landroid/content/res/TypedArray;.getType (I)I
03-08 17:51:06.625  14101-14101/downloader.download.downloader D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x0002
03-08 17:51:06.735  14101-14105/downloader.download.downloader D/dalvikvm﹕ GC_CONCURRENT freed 231K, 12% free 9513K/10759K, paused 16ms+2ms, total 52ms
03-08 17:51:06.765  14101-14101/downloader.download.downloader D/libEGL﹕ loaded /system/lib/egl/libEGL_mali.so
03-08 17:51:06.775  14101-14101/downloader.download.downloader D/libEGL﹕ loaded /system/lib/egl/libGLESv1_CM_mali.so
03-08 17:51:06.795  14101-14101/downloader.download.downloader D/libEGL﹕ loaded /system/lib/egl/libGLESv2_mali.so
03-08 17:51:06.815  14101-14101/downloader.download.downloader D/OpenGLRenderer﹕ Enabling debug mode 0
03-08 17:51:21.950  14101-14101/downloader.download.downloader W/IInputConnectionWrapper﹕ showStatusIcon on inactive InputConnection
03-08 17:51:36.054  14101-14101/downloader.download.downloader D/AndroidRuntime﹕ Shutting down VM
03-08 17:51:36.054  14101-14101/downloader.download.downloader W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x410bf2a0)
03-08 17:51:36.054  14101-14101/downloader.download.downloader E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.IllegalStateException: Could not execute method of the activity
            at android.view.View$1.onClick(View.java:3660)
            at android.view.View.performClick(View.java:4162)
            at android.view.View$PerformClick.run(View.java:17082)
            at android.os.Handler.handleCallback(Handler.java:615)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4867)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.reflect.InvocationTargetException
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at android.view.View$1.onClick(View.java:3655)
            at android.view.View.performClick(View.java:4162)
            at android.view.View$PerformClick.run(View.java:17082)
            at android.os.Handler.handleCallback(Handler.java:615)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4867)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at downloader.download.downloader.MainActivity.download(MainActivity.java:51)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at android.view.View$1.onClick(View.java:3655)
            at android.view.View.performClick(View.java:4162)
            at android.view.View$PerformClick.run(View.java:17082)
            at android.os.Handler.handleCallback(Handler.java:615)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4867)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

您正在 onCreate 中创建 EditText。

您声明了一个全局编辑文本，但您正在 OnCreate 上初始化一个新文本。执行下载方法时，您将从全局获取空指针。

这样做：

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        this.button = (Button) findViewById(R.id.button);
        this.editText = (EditText) findViewById(R.id.editText);