Here is my code for the bar chart in android Following error i get [closed]

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Here is the my main activity class

    package android.graph.graphview;

    import android.app.Activity;
    import android.graphics.Canvas;
    import android.os.Bundle;

    public class GraphView extends Activity {
/** Called when the activity is first created. */
GraphViewDemo mGraphViewDemo;
Canvas mCanvas = new Canvas();

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    mGraphViewDemo = (GraphViewDemo) findViewById(R.id.graphview);
    float[] values = new float[] { 1.0f, 6.0f, 7.0f, 8.0f, 9.0f, 3.0f,
            2.0f, 10.0f, 6.0f, 7.0f, 8.0f, 9.0f, 1.0f };
    String[] verlabels = new String[] { "great", "ok", "bad" };
    String[] horlabels = new String[] { "today", "tomorrow", "next week",
            "next month", "Next Year" };
    mGraphViewDemo = new GraphViewDemo(this, values, "GraphViewDemo",
            horlabels, verlabels, GraphViewDemo.BAR);
    mGraphViewDemo.draw(mCanvas);

}

}

Here is the my class where i define view for draw bar chart in GraphViewDemo.java

    package android.graph.graphview;

    import android.content.Context;
    import android.graphics.Canvas;
    import android.graphics.Color;
    import android.graphics.Paint;
    import android.graphics.Paint.Align;
    import android.util.AttributeSet;
    import android.util.Log;
    import android.view.View;

    public class GraphViewDemo extends View {

public static boolean BAR = true;
public static boolean LINE = false;

private Paint paint;
private float[] values;
private String[] horlabels;
private String[] verlabels;
private String title;
private boolean type;

public GraphViewDemo(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public GraphViewDemo(Context context, float[] values, String title,
        String[] horlabels, String[] verlabels, boolean type) {
    super(context);
    if (values == null)
        values = new float[0];
    else
        this.values = values;
    if (title == null)
        title = "";
    else
        this.title = title;
    if (horlabels == null)
        this.horlabels = new String[0];
    else
        this.horlabels = horlabels;
    if (verlabels == null)
        this.verlabels = new String[0];
    else
        this.verlabels = verlabels;
    this.type = type;
    paint = new Paint();
}

@Override
protected void onDraw(Canvas canvas) {
    float border = 20;
    float horstart = border * 2;
    float height = getHeight();
    float width = getWidth() - 1;
    float max = getMax();    << also here i get NPE error in my Logcat >>
    float min = getMin();
    float diff = max - min;
    float graphheight = height - (2 * border);
    float graphwidth = width - (2 * border);


    paint.setTextAlign(Align.LEFT);
    int vers = verlabels.length - 1;
    for (int i = 0; i < verlabels.length; i++) {
        // paint.setColor(Color.RED);
        float y = ((graphheight / vers) * i) + border;
        // canvas.drawLine(horstart, y, width, y, paint);
        paint.setColor(Color.WHITE);
        canvas.drawText(verlabels[i], 0, y, paint);
    }
    int hors = horlabels.length - 1;
    for (int i = 0; i < horlabels.length; i++) {
        // paint.setColor(Color.BLUE);
        float x = ((graphwidth / hors) * i) + horstart;
        // canvas.drawLine(x, height - 50, x, border, paint);
        paint.setTextAlign(Align.CENTER);
        if (i == horlabels.length - 1)
            paint.setTextAlign(Align.RIGHT);
        if (i == 0)
            paint.setTextAlign(Align.LEFT);
        paint.setColor(Color.WHITE);
        canvas.drawText(horlabels[i], x, height - 4, paint);
    }

    paint.setTextAlign(Align.CENTER);
    canvas.drawText(title, (graphwidth / 2) + horstart, border - 4, paint);

    if (max != min) {
        paint.setColor(Color.LTGRAY);
        if (type == BAR) {
            int minus = 10;
            float datalength = values.length;
            float colwidth = (width - (2 * border)) / datalength;
            for (int i = 0; i < values.length; i++) {
                float val = values[i] - min;
                float rat = val / diff;
                float h = graphheight * rat;
                canvas.drawRect((i * colwidth) + horstart,
                        ((border - h) + graphheight) + 100,
                        (((i * colwidth) + horstart) + (colwidth - 1))
                                - minus, ((height - (border - 1) - 50)),
                        paint);
                // (border - h)+ graphheight

            }

        }
    }
}

private float get开发者_开发知识库Max() {
    float largest = Integer.MIN_VALUE;
    for (int i = 0; i < values.length; i++)   <<in this line i get NPE
        // if (values[i] > largest)
        // largest = values[i];
        largest = 10;
    Log.v("log_tag", "All Data max of getmax " + largest);
    return largest;
}

private float getMin() {
    float smallest = Integer.MAX_VALUE;
    for (int i = 0; i < values.length; i++)
        // if (values[i] < smallest)
        smallest = -5;
    Log.v("log_tag", "All Data min get min  " + smallest);
    return smallest;
}

}

And Now here is my main.xml file

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TextView android:layout_width="fill_parent"
    android:layout_height="wrap_content" android:text="@string/hello" />
<android.graph.graphview.GraphViewDemo
    android:layout_width="wrap_content" android:layout_height="wrap_content"
    android:id="@+id/graphview" />
</LinearLayout>

Here is my error so please solved this.

    05-16 16:43:17.392: ERROR/AndroidRuntime(822): FATAL EXCEPTION: main
    05-16 16:43:17.392: ERROR/AndroidRuntime(822): java.lang.NullPointerException
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at            android.graph.graphview.GraphViewDemo.getMax(GraphViewDemo.java:159)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.graph.graphview.GraphViewDemo.onDraw(GraphViewDemo.java:57)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.View.draw(View.java:6740)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.ViewGroup.drawChild(ViewGroup.java:1640)      
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1367)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.ViewGroup.drawChild(ViewGroup.java:1638)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1367) 
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.View.draw(View.java:6743)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.widget.FrameLayout.draw(FrameLayout.java:352)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.ViewGroup.drawChild(ViewGroup.java:1640 )
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1367)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.ViewGroup.drawChild(ViewGroup.java:1638)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1367)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.View.draw(View.java:6743)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.widget.FrameLayout.draw(FrameLayout.java:352)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1842)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.ViewRoot.draw(ViewRoot.java:1407)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.ViewRoot.performTraversals(ViewRoot.java:1163)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1727)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.os.Handler.dispatchMessage(Handler.java:99)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.os.Looper.loop(Looper.java:123)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at android.app.ActivityThread.main(ActivityThread.java:4627)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at java.lang.reflect.Method.invokeNative(Native Method)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at java.lang.reflect.Method.invoke(Method.java:521)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
    05-16 16:43:17.392: ERROR/AndroidRuntime(822):     at dalvik.system.NativeStart.main(Native Method)

I want this solution in xml file not any content view so please check it.

---

mGraphViewDemo = new GraphViewDemo(this, values, "GraphViewDemo",
        horlabels, verlabels, GraphViewDemo.BAR);
mGraphViewDemo.draw(mCanvas);

I think, your intention was to overwrite the view object which is already inflated. This doesn't do this, so you still have the view, which is not properly initialized and thus getting NullPointerException. Remove the view from xml and simply add the created(in onCreate()) view to the layout.

setContentView(R.layout.main);
LinearLayout layout = (LinearLayout) findViewById(R.id.layout);// don't forget to mention id in xml
float[] values = new float[] { 1.0f, 6.0f, 7.0f, 8.0f, 9.0f, 3.0f,
        2.0f, 10.0f, 6.0f, 7.0f, 8.0f, 9.0f, 1.0f };
String[] verlabels = new String[] { "great", "ok", "bad" };
String[] horlabels = new String[] { "today", "tomorrow", "next week",
        "next month", "Next Year" };
mGraphViewDemo = new GraphViewDemo(this, values, "GraphViewDemo",
        horlabels, verlabels, GraphViewDemo.BAR);
layout.add(mGraphViewDemo);

Also, you should NOT instantiate a Canvas object, and you should NOT manually try to draw your view. All custom drawing must be placed in onDraw() method of the view.

---

The only reason for a NPE in getMax is values being equal to null.

And this is initiated in the constructor at this code:

public GraphViewDemo(Context context, float[] values, String title,
    String[] horlabels, String[] verlabels, boolean type) {
  super(context);

  if (values == null)
    values = new float[0];
  else
    this.values = values;

See what happens if you create an instance and pass null for values? The local variable values is initialized with a zero-size array while the class attribute values is still null.

This will fix the issue:

  if (values == null)
    this.values = new float[0];  // <-- change in this line
  else
    this.values = values;

(btw - a very common bug...)

---

The Javadoc for View states:

View(Context context, AttributeSet attrs)
    Constructor that is called when inflating a view from XML.

There is a good chance, that your actual View subclass instance has been created with the other constructor which is defined and does not init the fields. Simply add a log statement to the other constructors body to check if this is the case.