我想从文件选择器中拍摄照片并将其显示在图像视图中..但是当我运行我的应用程序时，它将被停止并且不起作用。哪里有问题？ 这段代码是'MainActivity.java'的代码。我没有更改我项目的其他文件中的任何内容。我的代码基于this link。我的代码是：
public class MainActivity extends Activity {
private static final int FILE_SELECT_CODE = 0;
private static final String TAG = null;
public TextView tv=(TextView) findViewById(R.id.textView1);
ImageView iv=(ImageView) findViewById(R.id.imageView1);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button b=(Button) findViewById(R.id.button1);
b.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
showFileChooser();
}
});
}
private void showFileChooser() {
Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
intent.setType("*/*");
intent.addCategory(Intent.CATEGORY_OPENABLE);
try {
startActivityForResult(
Intent.createChooser(intent, "Select a File to Upload"),
FILE_SELECT_CODE);
} catch (android.content.ActivityNotFoundException ex) {
// Potentially direct the user to the Market with a Dialog
Toast.makeText(this, "Please install a File Manager.",
Toast.LENGTH_SHORT).show();
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
switch (requestCode) {
case FILE_SELECT_CODE:
if (resultCode == RESULT_OK) {
// Get the Uri of the selected file
Uri uri = data.getData();
iv.setImageURI(uri);
Log.d(TAG, "File Uri: " + uri.toString());
}
break;
}
super.onActivityResult(requestCode, resultCode, data);
}
@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;
}
}
日志是：
12-12 04:21:32.343: D/AndroidRuntime(1068): Shutting down VM
12-12 04:21:32.343: W/dalvikvm(1068): threadid=1: thread exiting with uncaught exception (group=0xb4a60b90)
12-12 04:21:32.433: E/AndroidRuntime(1068): FATAL EXCEPTION: main
12-12 04:21:32.433: E/AndroidRuntime(1068): Process: com.example.a55j, PID: 1068
12-12 04:21:32.433: E/AndroidRuntime(1068): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.a55j/com.example.a55j.MainActivity}: java.lang.NullPointerException
12-12 04:21:32.433: E/AndroidRuntime(1068): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2102)
12-12 04:21:32.433: E/AndroidRuntime(1068): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
12-12 04:21:32.433: E/AndroidRuntime(1068): at android.app.ActivityThread.access$700(ActivityThread.java:135)
12-12 04:21:32.433: E/AndroidRuntime(1068): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
12-12 04:21:32.433: E/AndroidRuntime(1068): at android.os.Handler.dispatchMessage(Handler.java:102)
12-12 04:21:32.433: E/AndroidRuntime(1068): at android.os.Looper.loop(Looper.java:137)
12-12 04:21:32.433: E/AndroidRuntime(1068): at android.app.ActivityThread.main(ActivityThread.java:4998)
12-12 04:21:32.433: E/AndroidRuntime(1068): at java.lang.reflect.Method.invokeNative(Native Method)
12-12 04:21:32.433: E/AndroidRuntime(1068): at java.lang.reflect.Method.invoke(Method.java:515)
12-12 04:21:32.433: E/AndroidRuntime(1068): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
12-12 04:21:32.433: E/AndroidRuntime(1068): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
12-12 04:21:32.433: E/AndroidRuntime(1068): at dalvik.system.NativeStart.main(Native Method)
12-12 04:21:32.433: E/AndroidRuntime(1068): Caused by: java.lang.NullPointerException
12-12 04:21:32.433: E/AndroidRuntime(1068): at android.app.Activity.findViewById(Activity.java:1883)
12-12 04:21:32.433: E/AndroidRuntime(1068): at com.example.a55j.MainActivity.<init>(MainActivity.java:23)
12-12 04:21:32.433: E/AndroidRuntime(1068): at java.lang.Class.newInstanceImpl(Native Method)
12-12 04:21:32.433: E/AndroidRuntime(1068): at java.lang.Class.newInstance(Class.java:1208)
12-12 04:21:32.433: E/AndroidRuntime(1068): at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
12-12 04:21:32.433: E/AndroidRuntime(1068): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2093)
12-12 04:21:32.433: E/AndroidRuntime(1068): ... 11 more
12-12 04:21:34.823: I/Process(1068): Sending signal. PID: 1068 SIG: 9
activiyt_main xml是：
<RelativeLayout 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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/textView1"
android:layout_marginLeft="16dp"
android:layout_marginTop="35dp"
android:layout_toRightOf="@+id/textView1"
android:text="@string/open" />
<ImageView
android:id="@+id/imageView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/button1"
android:layout_marginTop="81dp"
android:layout_toLeftOf="@+id/button1"
android:src="@drawable/ic_launcher" />
</RelativeLayout>
答案 0 :(得分：1)
试试这个 -
public class MainActivity extends Activity {
private static final int FILE_SELECT_CODE = 0;
private static final String TAG = null;
public TextView tv;
public ImageView iv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv=(TextView) findViewById(R.id.textView1);
iv=(ImageView) findViewById(R.id.imageView1);
Button b=(Button) findViewById(R.id.button1);
b.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
showFileChooser();
}
});
}
private void showFileChooser() {
Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
intent.setType("*/*");
intent.addCategory(Intent.CATEGORY_OPENABLE);
try {
startActivityForResult(
Intent.createChooser(intent, "Select a File to Upload"),
FILE_SELECT_CODE);
} catch (android.content.ActivityNotFoundException ex) {
// Potentially direct the user to the Market with a Dialog
Toast.makeText(this, "Please install a File Manager.",
Toast.LENGTH_SHORT).show();
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
switch (requestCode) {
case FILE_SELECT_CODE:
if (resultCode == RESULT_OK) {
// Get the Uri of the selected file
Uri uri = data.getData();
iv.setImageURI(uri);
Log.d(TAG, "File Uri: " + uri.toString());
}
break;
}
super.onActivityResult(requestCode, resultCode, data);
}
@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;
}
}
答案 1 :(得分：0)
请参阅此at android.app.Activity.findViewById(Activity.java:1883)，这表示您的XML文件R.layout.activity_main没有名称为button1的按钮，请检查。
public TextView tv=(TextView) findViewById(R.id.textView1);
ImageView iv=(ImageView) findViewById(R.id.imageView1);
在设置内容视图后将其放入OnCreate中，即使在布局实际膨胀之前，您也试图访问它们，即此错误即将到来。
答案 2 :(得分：0)
试试这个。它正在我的机器上工作。
公共类MainActivity扩展了Activity {
private static final int FILE_SELECT_CODE = 0;
// private static final String TAG = null;
TextView tv;
ImageView iv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button b=(Button) findViewById(R.id.button1);
tv=(TextView) findViewById(R.id.textView1);
iv=(ImageView) findViewById(R.id.imageView1);
b.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
showFileChooser();
}
});
}
private void showFileChooser() {
Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
intent.setType("*/*");
intent.addCategory(Intent.CATEGORY_OPENABLE);
try {
startActivityForResult(
Intent.createChooser(intent, "Select a File to Upload"),
FILE_SELECT_CODE);
} catch (android.content.ActivityNotFoundException ex) {
// Potentially direct the user to the Market with a Dialog
Toast.makeText(this, "Please install a File Manager.",
Toast.LENGTH_SHORT).show();
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
switch (requestCode) {
case FILE_SELECT_CODE:
if (resultCode == RESULT_OK) {
// Get the Uri of the selected file
Uri uri = data.getData();
iv.setImageURI(uri);
// Log.d(TAG, "File Uri: " + uri.toString());
}
break;
}
super.onActivityResult(requestCode, resultCode, data);
}
@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;
}
}
答案 3 :(得分：0)
根据您LogCat error获得的NullPointerException
在全球范围内（ImageView之前）初始化您的{{1and1}}，例如
TextView并将OnCreate和ImageView iv;
TextView tv;
放在findViewById(R.id.imageView1)方法中。