我是一个新手Android开发人员,我正在制作,或者试图创建一个能够打开几乎所有文件类型的文件浏览器。从音乐文件,视频文件,文档文件和许多其他文件。但是,我遇到了一个巨大的问题,我的应用程序编译成功,但它没有打开。这是我的代码:
package com.tstudios.openit;
import android.app.AlertDialog;
import android.app.ListActivity;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import java.io.File;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
public class MainActivity extends ListActivity {
private List<String> item = null;
private List<String> path = null;
private String root;
private TextView myPath;
private ImageView mImageView=(ImageView) findViewById(R.id.gallery);
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
myPath = (TextView)findViewById(R.id.path);
root = Environment.getExternalStorageDirectory().getPath();
getDir(root);
}
private void getDir(String dirPath)
{
myPath.setText("Location: " + dirPath);
item = new ArrayList<String>();
path = new ArrayList<String>();
File f = new File(dirPath);
File[] files = f.listFiles();
if(!dirPath.equals(root))
{
item.add(root);
path.add(root);
item.add("../");
path.add(f.getParent());
}
String filename = f.getName();
String filenameArray[] = filename.split("\\.");
String extension = filenameArray[filenameArray.length-1];
TextView row=(TextView)findViewById(R.id.rowtext);
//if(extension=="jpg"){
//mImageView.setImageBitmap(BitmapFactory.decodeFile(dirPath));
//}
//if(extension!=null){
//row.setCompoundDrawablesWithIntrinsicBounds(R.drawable.ic_launcher,0,0,0);
//}
Arrays.sort(files, filecomparator);
for(int i=0; i < files.length; i++)
{
File file = files[i];
if(!file.isHidden() && file.canRead()){
path.add(file.getPath());
if(file.isDirectory()){
item.add(file.getName() + "/");
}else{
item.add(file.getName());
}
}
}
ArrayAdapter<String> fileList =
new ArrayAdapter<String>(this, R.layout.row, item);
setListAdapter(fileList);
}
Comparator<? super File> filecomparator = new Comparator<File>(){
public int compare(File file1, File file2) {
if(file1.isDirectory()){
if (file2.isDirectory()){
return String.valueOf(file1.getName().toLowerCase()).compareTo(file2.getName().toLowerCase());
}else{
return -1;
}
}else {
if (file2.isDirectory()){
return 1;
}else{
return String.valueOf(file1.getName().toLowerCase()).compareTo(file2.getName().toLowerCase());
}
}
}
};
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
// TODO Auto-generated method stub
File file = new File(path.get(position));
String filename = file.getName();
String filenameArray[] = filename.split("\\.");
String extension = filenameArray[filenameArray.length-1];
if (file.isDirectory())
{
if(extension=="jpg"){
mImageView.setImageBitmap(BitmapFactory.decodeFile(filename));
getDir(path.get(position));
}else{
new AlertDialog.Builder(this)
.setIcon(R.drawable.ic_launcher)
.setTitle("[" + file.getName() + "] folder can't be read!")
.setPositiveButton("OK", null).show();
}
}else {
new AlertDialog.Builder(this)
.setIcon(R.drawable.ic_launcher)
.setTitle("[" + file.getName() + "]")
.setPositiveButton("OK", null).show();
}
}
}
这是我在使用应用程序时获得的logcat,顺便说一下,如果有帮助,我会使用Sony Xperia Z1 Compact
08-28 12:10:54.779 4169-4169/com.tstudios.openit D/AndroidRuntime﹕ Shutting down VM
08-28 12:10:54.779 4169-4169/com.tstudios.openit W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x4164cd88)
08-28 12:10:54.789 4169-4169/com.tstudios.openit E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.tstudios.openit, PID: 4169
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.tstudios.openit/com.tstudios.openit.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2163)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2286)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:212)
at android.app.ActivityThread.main(ActivityThread.java:5135)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:877)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.app.Activity.findViewById(Activity.java:1884)
at com.tstudios.openit.MainActivity.<init>(MainActivity.java:25)
at java.lang.Class.newInstanceImpl(Native Method)
at java.lang.Class.newInstance(Class.java:1208)
at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2154)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2286)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:212)
at android.app.ActivityThread.main(ActivityThread.java:5135)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:877)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
at dalvik.system.NativeStart.main(Native Method)
另一个问题,如何在文件名之前放置图标?取决于扩展名 非常感谢你的帮助
答案 0 :(得分:3)
移动
mImageView=(ImageView) findViewById(R.id.gallery);
在onCreate()
之后到setContentView()
,只留下类级别的成员变量声明:
private ImageView mImageView;
在onCreate()
之前,还没有活动窗口,您将获得NPE。
在setContentView()
之前,没有要搜索的视图层次结构,并返回null。
答案 1 :(得分:1)
private ImageView mImageView=(ImageView) findViewById(R.id.gallery);
要使用findViewById
,您需要有效的Activity
。它是在附加活动后发生的
答案 2 :(得分:0)
在 setContentView 之后放置此行私有ImageView mImageView =(ImageView)findViewById(R.id.gallery); 。它将解决空指针异常。在此之后,如果你得到任何其他例外,请告诉。